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1 .TH LIBPNG 3 "February 23, 2024"
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2 .SH NAME
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3 libpng \- Portable Network Graphics (PNG) Reference Library 1.6.43
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4
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5 .SH SYNOPSIS
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6 \fB#include <png.h>\fP
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7
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8 \fBpng_uint_32 png_access_version_number (void);\fP
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9
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10 \fBvoid png_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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11
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12 \fBvoid png_build_grayscale_palette (int \fP\fIbit_depth\fP\fB, png_colorp \fIpalette\fP\fB);\fP
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13
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14 \fBpng_voidp png_calloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
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15
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16 \fBvoid png_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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17
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18 \fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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19
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20 \fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
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21
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22 \fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
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23
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24 \fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
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25
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26 \fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
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27
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28 \fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
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29
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30 \fBpng_structp png_create_read_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
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31
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32 \fBpng_structp png_create_read_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
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33
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34 \fBpng_structp png_create_write_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
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35
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36 \fBpng_structp png_create_write_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
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37
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38 \fBvoid png_data_freer (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIfreer\fP\fB, png_uint_32 \fImask\fP\fB);\fP
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39
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40 \fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
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41
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42 \fBvoid png_destroy_read_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fP\fIinfo_ptr_ptr\fP\fB, png_infopp \fIend_info_ptr_ptr\fP\fB);\fP
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43
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44 \fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
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45
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46 \fBvoid png_err (png_structp \fIpng_ptr\fP\fB);\fP
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47
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48 \fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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49
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50 \fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
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51
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52 \fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
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53
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54 \fBvoid png_free_default (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
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55
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56 \fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
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57
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58 \fBpng_byte png_get_bit_depth (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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59
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60 \fBpng_uint_32 png_get_bKGD (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
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61
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62 \fBpng_byte png_get_channels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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63
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64 \fBpng_uint_32 png_get_cHRM (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*white_x\fP\fB, double \fP\fI*white_y\fP\fB, double \fP\fI*red_x\fP\fB, double \fP\fI*red_y\fP\fB, double \fP\fI*green_x\fP\fB, double \fP\fI*green_y\fP\fB, double \fP\fI*blue_x\fP\fB, double \fI*blue_y\fP\fB);\fP
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65
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66 \fBpng_uint_32 png_get_cHRM_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*white_x\fP\fB, png_uint_32 \fP\fI*white_y\fP\fB, png_uint_32 \fP\fI*red_x\fP\fB, png_uint_32 \fP\fI*red_y\fP\fB, png_uint_32 \fP\fI*green_x\fP\fB, png_uint_32 \fP\fI*green_y\fP\fB, png_uint_32 \fP\fI*blue_x\fP\fB, png_uint_32 \fI*blue_y\fP\fB);\fP
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67
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68 \fBpng_uint_32 png_get_cHRM_XYZ (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*red_X\fP\fB, double \fP\fI*red_Y\fP\fB, double \fP\fI*red_Z\fP\fB, double \fP\fI*green_X\fP\fB, double \fP\fI*green_Y\fP\fB, double \fP\fI*green_Z\fP\fB, double \fP\fI*blue_X\fP\fB, double \fP\fI*blue_Y\fP\fB, double \fI*blue_Z\fP\fB);\fP
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69
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70 \fBpng_uint_32 png_get_cHRM_XYZ_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_fixed_point \fP\fI*int_red_X\fP\fB, png_fixed_point \fP\fI*int_red_Y\fP\fB, png_fixed_point \fP\fI*int_red_Z\fP\fB, png_fixed_point \fP\fI*int_green_X\fP\fB, png_fixed_point \fP\fI*int_green_Y\fP\fB, png_fixed_point \fP\fI*int_green_Z\fP\fB, png_fixed_point \fP\fI*int_blue_X\fP\fB, png_fixed_point \fP\fI*int_blue_Y\fP\fB, png_fixed_point \fI*int_blue_Z\fP\fB);\fP
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71
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72 \fBpng_uint_32 png_get_chunk_cache_max (png_const_structp \fIpng_ptr\fP\fB);\fP
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73
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74 \fBpng_alloc_size_t png_get_chunk_malloc_max (png_const_structp \fIpng_ptr\fP\fB);\fP
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75
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76 \fBpng_byte png_get_color_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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77
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78 \fBpng_uint_32 png_get_compression_buffer_size (png_const_structp \fIpng_ptr\fP\fB);\fP
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79
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80 \fBpng_byte png_get_compression_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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81
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82 \fBpng_byte png_get_copyright (png_const_structp \fIpng_ptr\fP\fB);\fP
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83
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84 \fBpng_uint_32 png_get_current_row_number \fI(png_const_structp\fP\fB);\fP
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85
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86 \fBpng_byte png_get_current_pass_number \fI(png_const_structp\fP\fB);\fP
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87
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88 \fBpng_voidp png_get_error_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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89
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90 \fBpng_byte png_get_filter_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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91
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92 \fBpng_uint_32 png_get_gAMA (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
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93
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94 \fBpng_uint_32 png_get_gAMA_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
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95
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96 \fBpng_byte png_get_header_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
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97
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98 \fBpng_byte png_get_header_version (png_const_structp \fIpng_ptr\fP\fB);\fP
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99
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100 \fBpng_uint_32 png_get_eXIf (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fI*exif\fP\fB);\fP
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101
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102 \fBpng_uint_32 png_get_eXIf_1 (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_unit_32 \fP\fI*num_exif\fP\fB, png_bytep \fI*exif\fP\fB);\fP
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103
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104 \fBpng_uint_32 png_get_hIST (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
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105
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106 \fBpng_uint_32 png_get_iCCP (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_bytepp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
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107
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108 \fBpng_uint_32 png_get_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*width\fP\fB, png_uint_32 \fP\fI*height\fP\fB, int \fP\fI*bit_depth\fP\fB, int \fP\fI*color_type\fP\fB, int \fP\fI*interlace_type\fP\fB, int \fP\fI*compression_type\fP\fB, int \fI*filter_type\fP\fB);\fP
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109
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110 \fBpng_uint_32 png_get_image_height (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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111
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112 \fBpng_uint_32 png_get_image_width (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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113
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114 \fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
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115
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116 \fBpng_byte png_get_interlace_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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117
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118 \fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP
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119
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120 \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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121
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122 \fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP
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123
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124 \fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
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125
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126 \fBint png_get_palette_max(png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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127
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128 \fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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129
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130 \fBpng_uint_32 png_get_oFFs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*offset_x\fP\fB, png_uint_32 \fP\fI*offset_y\fP\fB, int \fI*unit_type\fP\fB);\fP
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131
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132 \fBpng_uint_32 png_get_pCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fI*purpose\fP\fB, png_int_32 \fP\fI*X0\fP\fB, png_int_32 \fP\fI*X1\fP\fB, int \fP\fI*type\fP\fB, int \fP\fI*nparams\fP\fB, png_charp \fP\fI*units\fP\fB, png_charpp \fI*params\fP\fB);\fP
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133
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134 \fBpng_uint_32 png_get_pHYs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
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135
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136 \fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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137
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138 \fBpng_uint_32 png_get_pHYs_dpi (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
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139
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140 \fBpng_fixed_point png_get_pixel_aspect_ratio_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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141
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142 \fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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143
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144 \fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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145
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146 \fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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147
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148 \fBpng_uint_32 png_get_PLTE (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
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149
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150 \fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr\fP\fB);\fP
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151
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152 \fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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153
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154 \fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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155
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156 \fBpng_uint_32 png_get_sBIT (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
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157
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158 \fBvoid png_get_sCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, double* \fP\fIwidth\fP\fB, double* \fIheight\fP\fB);\fP
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159
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160 \fBvoid png_get_sCAL_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_fixed_pointp \fP\fIwidth\fP\fB, png_fixed_pointp \fIheight\fP\fB);\fP
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161
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162 \fBvoid png_get_sCAL_s (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_charpp \fP\fIwidth\fP\fB, png_charpp \fIheight\fP\fB);\fP
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163
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164 \fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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jpayne@68
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165
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166 \fBpng_uint_32 png_get_sPLT (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
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167
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168 \fBpng_uint_32 png_get_sRGB (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int \fI*file_srgb_intent\fP\fB);\fP
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169
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170 \fBpng_uint_32 png_get_text (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
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171
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172 \fBpng_uint_32 png_get_tIME (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
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173
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174 \fBpng_uint_32 png_get_tRNS (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans_alpha\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_color\fP\fB);\fP
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175
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176 \fB/* This function is really an inline macro. \fI*/
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177
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178 \fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
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179
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180 \fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP
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181
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jpayne@68
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182 \fB/* This function is really an inline macro. \fI*/
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183
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184 \fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
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185
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186 \fBpng_uint_32 png_get_unknown_chunks (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
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187
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188 \fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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189
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190 \fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP
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191
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192 \fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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193
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194 \fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP
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195
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196 \fBpng_uint_32 png_get_valid (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
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197
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198 \fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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199
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200 \fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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jpayne@68
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201
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202 \fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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jpayne@68
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203
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204 \fBpng_int_32 png_get_x_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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205
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206 \fBpng_uint_32 png_get_x_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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jpayne@68
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207
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208 \fBpng_uint_32 png_get_x_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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jpayne@68
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209
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210 \fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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jpayne@68
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211
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jpayne@68
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212 \fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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jpayne@68
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213
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214 \fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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215
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216 \fBpng_int_32 png_get_y_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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jpayne@68
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217
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218 \fBpng_uint_32 png_get_y_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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219
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220 \fBpng_uint_32 png_get_y_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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221
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222 \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
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223
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224 \fBint png_image_begin_read_from_file (png_imagep \fP\fIimage\fP\fB, const char \fI*file_name\fP\fB);\fP
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225
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226 \fBint png_image_begin_read_from_stdio (png_imagep \fP\fIimage\fP\fB, FILE* \fIfile\fP\fB);\fP
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227
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228 \fBint, png_image_begin_read_from_memory (png_imagep \fP\fIimage\fP\fB, png_const_voidp \fP\fImemory\fP\fB, size_t \fIsize\fP\fB);\fP
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229
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230 \fBint png_image_finish_read (png_imagep \fP\fIimage\fP\fB, png_colorp \fP\fIbackground\fP\fB, void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap\fP\fB);\fP
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231
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jpayne@68
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232 \fBvoid png_image_free (png_imagep \fIimage\fP\fB);\fP
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233
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234 \fBint png_image_write_to_file (png_imagep \fP\fIimage\fP\fB, const char \fP\fI*file\fP\fB, int \fP\fIconvert_to_8bit\fP\fB, const void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap\fP\fB);\fP
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235
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236 \fBint png_image_write_to_memory (png_imagep \fP\fIimage\fP\fB, void \fP\fI*memory\fP\fB, png_alloc_size_t * PNG_RESTRICT \fP\fImemory_bytes\fP\fB, int \fP\fIconvert_to_8_bit\fP\fB, const void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, const void \fI*colormap\fP\fB);\fP
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237
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238 \fBint png_image_write_to_stdio (png_imagep \fP\fIimage\fP\fB, FILE \fP\fI*file\fP\fB, int \fP\fIconvert_to_8_bit\fP\fB, const void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap\fP\fB);\fP
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239
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240 \fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, size_t \fIpng_info_struct_size\fP\fB);\fP
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241
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jpayne@68
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242 \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
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243
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244 \fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP
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245
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246 \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
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247
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248 \fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
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249
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250 \fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
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251
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252 \fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP
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253
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254 \fBvoid png_process_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fIbuffer\fP\fB, size_t \fIbuffer_size\fP\fB);\fP
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255
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256 \fBsize_t png_process_data_pause (png_structp \fP\fIpng_ptr\fP\fB, int \fIsave\fP\fB);\fP
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257
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258 \fBpng_uint_32 png_process_data_skip (png_structp \fP\fIpng_ptr\fP\fB);\fP
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259
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260 \fBvoid png_progressive_combine_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIold_row\fP\fB, png_bytep \fInew_row\fP\fB);\fP
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261
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262 \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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263
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264 \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
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265
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266 \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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267
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268 \fBvoid png_read_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
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269
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270 \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
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271
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272 \fBvoid png_read_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_bytepp \fP\fIdisplay_row\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
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273
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274 \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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275
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276 \fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP
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277
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278 \fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
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279
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280 \fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
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281
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282 \fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
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283
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284 \fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
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285
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286 \fBvoid png_set_alpha_mode (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, double \fIoutput_gamma\fP\fB);\fP
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287
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288 \fBvoid png_set_alpha_mode_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, png_fixed_point \fIoutput_gamma\fP\fB);\fP
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289
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290 \fBvoid png_set_background (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, double \fIbackground_gamma\fP\fB);\fP
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291
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292 \fBvoid png_set_background_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, png_uint_32 \fIbackground_gamma\fP\fB);\fP
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293
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294 \fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
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295
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jpayne@68
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296 \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
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297
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298 \fBvoid png_set_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fIbackground\fP\fB);\fP
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299
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300 \fBvoid png_set_check_for_invalid_index (png_structrp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
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301
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302 \fBvoid png_set_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIwhite_x\fP\fB, double \fP\fIwhite_y\fP\fB, double \fP\fIred_x\fP\fB, double \fP\fIred_y\fP\fB, double \fP\fIgreen_x\fP\fB, double \fP\fIgreen_y\fP\fB, double \fP\fIblue_x\fP\fB, double \fIblue_y\fP\fB);\fP
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303
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304 \fBvoid png_set_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwhite_x\fP\fB, png_uint_32 \fP\fIwhite_y\fP\fB, png_uint_32 \fP\fIred_x\fP\fB, png_uint_32 \fP\fIred_y\fP\fB, png_uint_32 \fP\fIgreen_x\fP\fB, png_uint_32 \fP\fIgreen_y\fP\fB, png_uint_32 \fP\fIblue_x\fP\fB, png_uint_32 \fIblue_y\fP\fB);\fP
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305
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306 \fBvoid png_set_cHRM_XYZ (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIred_X\fP\fB, double \fP\fIred_Y\fP\fB, double \fP\fIred_Z\fP\fB, double \fP\fIgreen_X\fP\fB, double \fP\fIgreen_Y\fP\fB, double \fP\fIgreen_Z\fP\fB, double \fP\fIblue_X\fP\fB, double \fP\fIblue_Y\fP\fB, double \fIblue_Z\fP\fB);\fP
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307
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308 \fBvoid png_set_cHRM_XYZ_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_fixed_point \fP\fIint_red_X\fP\fB, png_fixed_point \fP\fIint_red_Y\fP\fB, png_fixed_point \fP\fIint_red_Z\fP\fB, png_fixed_point \fP\fIint_green_X\fP\fB, png_fixed_point \fP\fIint_green_Y\fP\fB, png_fixed_point \fP\fIint_green_Z\fP\fB, png_fixed_point \fP\fIint_blue_X\fP\fB, png_fixed_point \fP\fIint_blue_Y\fP\fB, png_fixed_point \fIint_blue_Z\fP\fB);\fP
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309
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310 \fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
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311
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312 \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
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313
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314 \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
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315
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316 \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
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317
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318 \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
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319
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320 \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
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jpayne@68
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321
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322 \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
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323
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324 \fBvoid png_set_error_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarning_fn\fP\fB);\fP
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jpayne@68
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325
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326 \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
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327
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328 \fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP
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329
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330 \fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
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331
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332 \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
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jpayne@68
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333
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334 \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
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335
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336 \fBvoid png_set_filter_heuristics (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_doublep \fP\fIfilter_weights\fP\fB, png_doublep \fIfilter_costs\fP\fB);\fP
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337
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338 \fBvoid png_set_filter_heuristics_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_fixed_point_p \fP\fIfilter_weights\fP\fB, png_fixed_point_p \fIfilter_costs\fP\fB);\fP
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jpayne@68
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339
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340 \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
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341
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342 \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
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jpayne@68
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343
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344 \fBvoid png_set_gamma_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIscreen_gamma\fP\fB, png_uint_32 \fIdefault_file_gamma\fP\fB);\fP
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345
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346 \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
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347
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348 \fBvoid png_set_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIfile_gamma\fP\fB);\fP
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349
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350 \fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
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351
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352 \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
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353
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354 \fBvoid png_set_eXIf (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fIexif\fP\fB);\fP
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355
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356 \fBvoid png_set_eXIf_1 (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fInum_exif\fP\fB, png_bytep \fIexif\fP\fB);\fP
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jpayne@68
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357
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358 \fBvoid png_set_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fIhist\fP\fB);\fP
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359
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360 \fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_const_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_const_bytep \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
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361
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362 \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
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363
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364 \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
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365
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366 \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
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367
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368 \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
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369
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370 \fBvoid png_set_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwidth\fP\fB, png_uint_32 \fP\fIheight\fP\fB, int \fP\fIbit_depth\fP\fB, int \fP\fIcolor_type\fP\fB, int \fP\fIinterlace_type\fP\fB, int \fP\fIcompression_type\fP\fB, int \fIfilter_type\fP\fB);\fP
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371
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372 \fBvoid png_set_keep_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIkeep\fP\fB, png_bytep \fP\fIchunk_list\fP\fB, int \fInum_chunks\fP\fB);\fP
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373
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374 \fBjmp_buf* png_set_longjmp_fn (png_structp \fP\fIpng_ptr\fP\fB, png_longjmp_ptr \fP\fIlongjmp_fn\fP\fB, size_t \fIjmp_buf_size\fP\fB);\fP
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375
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376 \fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
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377
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378 \fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
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379
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380 \fBvoid png_set_mem_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
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jpayne@68
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381
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382 \fBvoid png_set_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIoffset_x\fP\fB, png_uint_32 \fP\fIoffset_y\fP\fB, int \fIunit_type\fP\fB);\fP
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383
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384 \fBint png_set_option(png_structrp \fP\fIpng_ptr\fP\fB, int \fP\fIoption\fP\fB, int \fIonoff\fP\fB);\fP
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jpayne@68
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385
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386 \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
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387
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388 \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
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389
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390 \fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
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391
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392 \fBvoid png_set_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIpurpose\fP\fB, png_int_32 \fP\fIX0\fP\fB, png_int_32 \fP\fIX1\fP\fB, int \fP\fItype\fP\fB, int \fP\fInparams\fP\fB, png_charp \fP\fIunits\fP\fB, png_charpp \fIparams\fP\fB);\fP
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393
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394 \fBvoid png_set_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIres_x\fP\fB, png_uint_32 \fP\fIres_y\fP\fB, int \fIunit_type\fP\fB);\fP
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395
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396 \fBvoid png_set_progressive_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIprogressive_ptr\fP\fB, png_progressive_info_ptr \fP\fIinfo_fn\fP\fB, png_progressive_row_ptr \fP\fIrow_fn\fP\fB, png_progressive_end_ptr \fIend_fn\fP\fB);\fP
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397
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398 \fBvoid png_set_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fInum_palette\fP\fB);\fP
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jpayne@68
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399
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400 \fBvoid png_set_quantize (png_structp \fP\fIpng_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fP\fInum_palette\fP\fB, int \fP\fImaximum_colors\fP\fB, png_uint_16p \fP\fIhistogram\fP\fB, int \fIfull_quantize\fP\fB);\fP
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jpayne@68
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401
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402 \fBvoid png_set_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fIread_data_fn\fP\fB);\fP
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jpayne@68
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403
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404 \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
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jpayne@68
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405
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406 \fBvoid png_set_read_user_chunk_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_chunk_ptr\fP\fB, png_user_chunk_ptr \fIread_user_chunk_fn\fP\fB);\fP
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jpayne@68
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407
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408 \fBvoid png_set_read_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIread_user_transform_fn\fP\fB);\fP
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jpayne@68
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409
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410 \fBvoid png_set_rgb_to_gray (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIerror_action\fP\fB, double \fP\fIred\fP\fB, double \fIgreen\fP\fB);\fP
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jpayne@68
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411
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412 \fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_uint_32 \fP\fIred\fP\fB, png_uint_32 \fIgreen\fP\fB);\fP
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413
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414 \fBvoid png_set_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytepp \fIrow_pointers\fP\fB);\fP
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415
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416 \fBvoid png_set_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fIsig_bit\fP\fB);\fP
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jpayne@68
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417
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418 \fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
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419
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420 \fBvoid png_set_sCAL_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_fixed_point \fP\fIwidth\fP\fB, png_fixed_point \fIheight\fP\fB);\fP
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jpayne@68
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421
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422 \fBvoid png_set_sCAL_s (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_charp \fP\fIwidth\fP\fB, png_charp \fIheight\fP\fB);\fP
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423
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424 \fBvoid png_set_scale_16 (png_structp \fIpng_ptr\fP\fB);\fP
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425
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426 \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
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427
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428 \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
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429
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430 \fBvoid png_set_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fP\fIsplt_ptr\fP\fB, int \fInum_spalettes\fP\fB);\fP
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431
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432 \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
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433
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434 \fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
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435
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436 \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
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437
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438 \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
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439
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440 \fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP
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441
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442 \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
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443
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444 \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
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445
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446 \fBvoid png_set_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fItext_ptr\fP\fB, int \fInum_text\fP\fB);\fP
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jpayne@68
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447
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jpayne@68
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448 \fBvoid png_set_text_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
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jpayne@68
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449
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jpayne@68
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450 \fBvoid png_set_text_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
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jpayne@68
|
451
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jpayne@68
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452 \fBvoid png_set_text_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
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jpayne@68
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453
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jpayne@68
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454 \fBvoid png_set_text_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
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|
jpayne@68
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455
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jpayne@68
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456 \fBvoid png_set_text_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
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jpayne@68
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457
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jpayne@68
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458 \fBvoid png_set_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fImod_time\fP\fB);\fP
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jpayne@68
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459
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jpayne@68
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460 \fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans_alpha\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_color\fP\fB);\fP
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jpayne@68
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461
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jpayne@68
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462 \fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP
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jpayne@68
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463
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jpayne@68
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464 \fBpng_uint_32 png_set_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkp \fP\fIunknowns\fP\fB, int \fP\fInum\fP\fB, int \fIlocation\fP\fB);\fP
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jpayne@68
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465
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jpayne@68
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466 \fBvoid png_set_unknown_chunk_location (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIchunk\fP\fB, int \fIlocation\fP\fB);\fP
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jpayne@68
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467
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jpayne@68
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468 \fBvoid png_set_user_limits (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIuser_width_max\fP\fB, png_uint_32 \fIuser_height_max\fP\fB);\fP
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jpayne@68
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469
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jpayne@68
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470 \fBvoid png_set_user_transform_info (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_transform_ptr\fP\fB, int \fP\fIuser_transform_depth\fP\fB, int \fIuser_transform_channels\fP\fB);\fP
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jpayne@68
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471
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|
jpayne@68
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472 \fBvoid png_set_write_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fP\fIwrite_data_fn\fP\fB, png_flush_ptr \fIoutput_flush_fn\fP\fB);\fP
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jpayne@68
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473
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jpayne@68
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474 \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
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jpayne@68
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475
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jpayne@68
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476 \fBvoid png_set_write_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIwrite_user_transform_fn\fP\fB);\fP
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|
jpayne@68
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477
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jpayne@68
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478 \fBint png_sig_cmp (png_bytep \fP\fIsig\fP\fB, size_t \fP\fIstart\fP\fB, size_t \fInum_to_check\fP\fB);\fP
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jpayne@68
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479
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|
jpayne@68
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480 \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
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|
jpayne@68
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481
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jpayne@68
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482 \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
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jpayne@68
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483
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jpayne@68
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484 \fBvoid png_write_chunk (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_bytep \fP\fIdata\fP\fB, size_t \fIlength\fP\fB);\fP
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jpayne@68
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485
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jpayne@68
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486 \fBvoid png_write_chunk_data (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIdata\fP\fB, size_t \fIlength\fP\fB);\fP
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jpayne@68
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487
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jpayne@68
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488 \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
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|
jpayne@68
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489
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|
jpayne@68
|
490 \fBvoid png_write_chunk_start (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_uint_32 \fIlength\fP\fB);\fP
|
|
jpayne@68
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491
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jpayne@68
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492 \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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jpayne@68
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493
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|
jpayne@68
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494 \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
|
|
jpayne@68
|
495
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|
jpayne@68
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496 \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
|
|
jpayne@68
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497
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jpayne@68
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498 \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|
jpayne@68
|
499
|
|
jpayne@68
|
500 \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|
jpayne@68
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501
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|
jpayne@68
|
502 \fBvoid png_write_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
|
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jpayne@68
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503
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jpayne@68
|
504 \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
|
|
jpayne@68
|
505
|
|
jpayne@68
|
506 \fBvoid png_write_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
|
|
jpayne@68
|
507
|
|
jpayne@68
|
508 \fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
|
|
jpayne@68
|
509
|
|
jpayne@68
|
510 .SH DESCRIPTION
|
|
jpayne@68
|
511 The
|
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jpayne@68
|
512 .I libpng
|
|
jpayne@68
|
513 library supports encoding, decoding, and various manipulations of
|
|
jpayne@68
|
514 the Portable Network Graphics (PNG) format image files. It uses the
|
|
jpayne@68
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515 .IR zlib(3)
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jpayne@68
|
516 compression library.
|
|
jpayne@68
|
517 Following is a copy of the libpng-manual.txt file that accompanies libpng.
|
|
jpayne@68
|
518
|
|
jpayne@68
|
519 .SH LIBPNG.TXT
|
|
jpayne@68
|
520 libpng-manual.txt - A description on how to use and modify libpng
|
|
jpayne@68
|
521
|
|
jpayne@68
|
522 Copyright (c) 2018-2024 Cosmin Truta
|
|
jpayne@68
|
523 Copyright (c) 1998-2018 Glenn Randers-Pehrson
|
|
jpayne@68
|
524
|
|
jpayne@68
|
525 This document is released under the libpng license.
|
|
jpayne@68
|
526 For conditions of distribution and use, see the disclaimer
|
|
jpayne@68
|
527 and license in png.h
|
|
jpayne@68
|
528
|
|
jpayne@68
|
529 Based on:
|
|
jpayne@68
|
530
|
|
jpayne@68
|
531 libpng version 1.6.36, December 2018, through 1.6.43 - February 2024
|
|
jpayne@68
|
532 Updated and distributed by Cosmin Truta
|
|
jpayne@68
|
533 Copyright (c) 2018-2024 Cosmin Truta
|
|
jpayne@68
|
534
|
|
jpayne@68
|
535 libpng versions 0.97, January 1998, through 1.6.35 - July 2018
|
|
jpayne@68
|
536 Updated and distributed by Glenn Randers-Pehrson
|
|
jpayne@68
|
537 Copyright (c) 1998-2018 Glenn Randers-Pehrson
|
|
jpayne@68
|
538
|
|
jpayne@68
|
539 libpng 1.0 beta 6 - version 0.96 - May 28, 1997
|
|
jpayne@68
|
540 Updated and distributed by Andreas Dilger
|
|
jpayne@68
|
541 Copyright (c) 1996, 1997 Andreas Dilger
|
|
jpayne@68
|
542
|
|
jpayne@68
|
543 libpng 1.0 beta 2 - version 0.88 - January 26, 1996
|
|
jpayne@68
|
544 For conditions of distribution and use, see copyright
|
|
jpayne@68
|
545 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
|
|
jpayne@68
|
546 Schalnat, Group 42, Inc.
|
|
jpayne@68
|
547
|
|
jpayne@68
|
548 Updated/rewritten per request in the libpng FAQ
|
|
jpayne@68
|
549 Copyright (c) 1995, 1996 Frank J. T. Wojcik
|
|
jpayne@68
|
550 December 18, 1995 & January 20, 1996
|
|
jpayne@68
|
551
|
|
jpayne@68
|
552 TABLE OF CONTENTS
|
|
jpayne@68
|
553
|
|
jpayne@68
|
554 I. Introduction
|
|
jpayne@68
|
555 II. Structures
|
|
jpayne@68
|
556 III. Reading
|
|
jpayne@68
|
557 IV. Writing
|
|
jpayne@68
|
558 V. Simplified API
|
|
jpayne@68
|
559 VI. Modifying/Customizing libpng
|
|
jpayne@68
|
560 VII. MNG support
|
|
jpayne@68
|
561 VIII. Changes to Libpng from version 0.88
|
|
jpayne@68
|
562 IX. Changes to Libpng from version 1.0.x to 1.2.x
|
|
jpayne@68
|
563 X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
|
|
jpayne@68
|
564 XI. Changes to Libpng from version 1.4.x to 1.5.x
|
|
jpayne@68
|
565 XII. Changes to Libpng from version 1.5.x to 1.6.x
|
|
jpayne@68
|
566 XIII. Detecting libpng
|
|
jpayne@68
|
567 XIV. Source code repository
|
|
jpayne@68
|
568 XV. Coding style
|
|
jpayne@68
|
569
|
|
jpayne@68
|
570 .SH I. Introduction
|
|
jpayne@68
|
571
|
|
jpayne@68
|
572 This file describes how to use and modify the PNG reference library
|
|
jpayne@68
|
573 (known as libpng) for your own use. In addition to this
|
|
jpayne@68
|
574 file, example.c is a good starting point for using the library, as
|
|
jpayne@68
|
575 it is heavily commented and should include everything most people
|
|
jpayne@68
|
576 will need. We assume that libpng is already installed; see the
|
|
jpayne@68
|
577 INSTALL file for instructions on how to configure and install libpng.
|
|
jpayne@68
|
578
|
|
jpayne@68
|
579 For examples of libpng usage, see the files "example.c", "pngtest.c",
|
|
jpayne@68
|
580 and the files in the "contrib" directory, all of which are included in
|
|
jpayne@68
|
581 the libpng distribution.
|
|
jpayne@68
|
582
|
|
jpayne@68
|
583 Libpng was written as a companion to the PNG specification, as a way
|
|
jpayne@68
|
584 of reducing the amount of time and effort it takes to support the PNG
|
|
jpayne@68
|
585 file format in application programs.
|
|
jpayne@68
|
586
|
|
jpayne@68
|
587 The PNG specification (second edition), November 2003, is available as
|
|
jpayne@68
|
588 a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2004 (E)) at
|
|
jpayne@68
|
589 <https://www.w3.org/TR/2003/REC-PNG-20031110/>.
|
|
jpayne@68
|
590 The W3C and ISO documents have identical technical content.
|
|
jpayne@68
|
591
|
|
jpayne@68
|
592 The PNG-1.2 specification is available at
|
|
jpayne@68
|
593 <https://png-mng.sourceforge.io/pub/png/spec/1.2/>.
|
|
jpayne@68
|
594 It is technically equivalent
|
|
jpayne@68
|
595 to the PNG specification (second edition) but has some additional material.
|
|
jpayne@68
|
596
|
|
jpayne@68
|
597 The PNG-1.0 specification is available as RFC 2083 at
|
|
jpayne@68
|
598 <https://png-mng.sourceforge.io/pub/png/spec/1.0/> and as a
|
|
jpayne@68
|
599 W3C Recommendation at <https://www.w3.org/TR/REC-png-961001>.
|
|
jpayne@68
|
600
|
|
jpayne@68
|
601 Some additional chunks are described in the special-purpose public chunks
|
|
jpayne@68
|
602 documents at <http://www.libpng.org/pub/png/spec/register/>
|
|
jpayne@68
|
603
|
|
jpayne@68
|
604 Other information
|
|
jpayne@68
|
605 about PNG, and the latest version of libpng, can be found at the PNG home
|
|
jpayne@68
|
606 page, <http://www.libpng.org/pub/png/>.
|
|
jpayne@68
|
607
|
|
jpayne@68
|
608 Most users will not have to modify the library significantly; advanced
|
|
jpayne@68
|
609 users may want to modify it more. All attempts were made to make it as
|
|
jpayne@68
|
610 complete as possible, while keeping the code easy to understand.
|
|
jpayne@68
|
611 Currently, this library only supports C. Support for other languages
|
|
jpayne@68
|
612 is being considered.
|
|
jpayne@68
|
613
|
|
jpayne@68
|
614 Libpng has been designed to handle multiple sessions at one time,
|
|
jpayne@68
|
615 to be easily modifiable, to be portable to the vast majority of
|
|
jpayne@68
|
616 machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
|
|
jpayne@68
|
617 to use. The ultimate goal of libpng is to promote the acceptance of
|
|
jpayne@68
|
618 the PNG file format in whatever way possible. While there is still
|
|
jpayne@68
|
619 work to be done (see the TODO file), libpng should cover the
|
|
jpayne@68
|
620 majority of the needs of its users.
|
|
jpayne@68
|
621
|
|
jpayne@68
|
622 Libpng uses zlib for its compression and decompression of PNG files.
|
|
jpayne@68
|
623 Further information about zlib, and the latest version of zlib, can
|
|
jpayne@68
|
624 be found at the zlib home page, <https://zlib.net/>.
|
|
jpayne@68
|
625 The zlib compression utility is a general purpose utility that is
|
|
jpayne@68
|
626 useful for more than PNG files, and can be used without libpng.
|
|
jpayne@68
|
627 See the documentation delivered with zlib for more details.
|
|
jpayne@68
|
628 You can usually find the source files for the zlib utility wherever you
|
|
jpayne@68
|
629 find the libpng source files.
|
|
jpayne@68
|
630
|
|
jpayne@68
|
631 Libpng is thread safe, provided the threads are using different
|
|
jpayne@68
|
632 instances of the structures. Each thread should have its own
|
|
jpayne@68
|
633 png_struct and png_info instances, and thus its own image.
|
|
jpayne@68
|
634 Libpng does not protect itself against two threads using the
|
|
jpayne@68
|
635 same instance of a structure.
|
|
jpayne@68
|
636
|
|
jpayne@68
|
637 .SH II. Structures
|
|
jpayne@68
|
638
|
|
jpayne@68
|
639 There are two main structures that are important to libpng, png_struct
|
|
jpayne@68
|
640 and png_info. Both are internal structures that are no longer exposed
|
|
jpayne@68
|
641 in the libpng interface (as of libpng 1.5.0).
|
|
jpayne@68
|
642
|
|
jpayne@68
|
643 The png_info structure is designed to provide information about the
|
|
jpayne@68
|
644 PNG file. At one time, the fields of png_info were intended to be
|
|
jpayne@68
|
645 directly accessible to the user. However, this tended to cause problems
|
|
jpayne@68
|
646 with applications using dynamically loaded libraries, and as a result
|
|
jpayne@68
|
647 a set of interface functions for png_info (the png_get_*() and png_set_*()
|
|
jpayne@68
|
648 functions) was developed, and direct access to the png_info fields was
|
|
jpayne@68
|
649 deprecated..
|
|
jpayne@68
|
650
|
|
jpayne@68
|
651 The png_struct structure is the object used by the library to decode a
|
|
jpayne@68
|
652 single image. As of 1.5.0 this structure is also not exposed.
|
|
jpayne@68
|
653
|
|
jpayne@68
|
654 Almost all libpng APIs require a pointer to a png_struct as the first argument.
|
|
jpayne@68
|
655 Many (in particular the png_set and png_get APIs) also require a pointer
|
|
jpayne@68
|
656 to png_info as the second argument. Some application visible macros
|
|
jpayne@68
|
657 defined in png.h designed for basic data access (reading and writing
|
|
jpayne@68
|
658 integers in the PNG format) don't take a png_info pointer, but it's almost
|
|
jpayne@68
|
659 always safe to assume that a (png_struct*) has to be passed to call an API
|
|
jpayne@68
|
660 function.
|
|
jpayne@68
|
661
|
|
jpayne@68
|
662 You can have more than one png_info structure associated with an image,
|
|
jpayne@68
|
663 as illustrated in pngtest.c, one for information valid prior to the
|
|
jpayne@68
|
664 IDAT chunks and another (called "end_info" below) for things after them.
|
|
jpayne@68
|
665
|
|
jpayne@68
|
666 The png.h header file is an invaluable reference for programming with libpng.
|
|
jpayne@68
|
667 And while I'm on the topic, make sure you include the libpng header file:
|
|
jpayne@68
|
668
|
|
jpayne@68
|
669 #include <png.h>
|
|
jpayne@68
|
670
|
|
jpayne@68
|
671 and also (as of libpng-1.5.0) the zlib header file, if you need it:
|
|
jpayne@68
|
672
|
|
jpayne@68
|
673 #include <zlib.h>
|
|
jpayne@68
|
674
|
|
jpayne@68
|
675 .SS Types
|
|
jpayne@68
|
676
|
|
jpayne@68
|
677 The png.h header file defines a number of integral types used by the
|
|
jpayne@68
|
678 APIs. Most of these are fairly obvious; for example types corresponding
|
|
jpayne@68
|
679 to integers of particular sizes and types for passing color values.
|
|
jpayne@68
|
680
|
|
jpayne@68
|
681 One exception is how non-integral numbers are handled. For application
|
|
jpayne@68
|
682 convenience most APIs that take such numbers have C (double) arguments;
|
|
jpayne@68
|
683 however, internally PNG, and libpng, use 32 bit signed integers and encode
|
|
jpayne@68
|
684 the value by multiplying by 100,000. As of libpng 1.5.0 a convenience
|
|
jpayne@68
|
685 macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point)
|
|
jpayne@68
|
686 which is simply (png_int_32).
|
|
jpayne@68
|
687
|
|
jpayne@68
|
688 All APIs that take (double) arguments also have a matching API that
|
|
jpayne@68
|
689 takes the corresponding fixed point integer arguments. The fixed point
|
|
jpayne@68
|
690 API has the same name as the floating point one with "_fixed" appended.
|
|
jpayne@68
|
691 The actual range of values permitted in the APIs is frequently less than
|
|
jpayne@68
|
692 the full range of (png_fixed_point) (\-21474 to +21474). When APIs require
|
|
jpayne@68
|
693 a non-negative argument the type is recorded as png_uint_32 above. Consult
|
|
jpayne@68
|
694 the header file and the text below for more information.
|
|
jpayne@68
|
695
|
|
jpayne@68
|
696 Special care must be take with sCAL chunk handling because the chunk itself
|
|
jpayne@68
|
697 uses non-integral values encoded as strings containing decimal floating point
|
|
jpayne@68
|
698 numbers. See the comments in the header file.
|
|
jpayne@68
|
699
|
|
jpayne@68
|
700 .SS Configuration
|
|
jpayne@68
|
701
|
|
jpayne@68
|
702 The main header file function declarations are frequently protected by C
|
|
jpayne@68
|
703 preprocessing directives of the form:
|
|
jpayne@68
|
704
|
|
jpayne@68
|
705 #ifdef PNG_feature_SUPPORTED
|
|
jpayne@68
|
706 declare-function
|
|
jpayne@68
|
707 #endif
|
|
jpayne@68
|
708 ...
|
|
jpayne@68
|
709 #ifdef PNG_feature_SUPPORTED
|
|
jpayne@68
|
710 use-function
|
|
jpayne@68
|
711 #endif
|
|
jpayne@68
|
712
|
|
jpayne@68
|
713 The library can be built without support for these APIs, although a
|
|
jpayne@68
|
714 standard build will have all implemented APIs. Application programs
|
|
jpayne@68
|
715 should check the feature macros before using an API for maximum
|
|
jpayne@68
|
716 portability. From libpng 1.5.0 the feature macros set during the build
|
|
jpayne@68
|
717 of libpng are recorded in the header file "pnglibconf.h" and this file
|
|
jpayne@68
|
718 is always included by png.h.
|
|
jpayne@68
|
719
|
|
jpayne@68
|
720 If you don't need to change the library configuration from the default, skip to
|
|
jpayne@68
|
721 the next section ("Reading").
|
|
jpayne@68
|
722
|
|
jpayne@68
|
723 Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all
|
|
jpayne@68
|
724 of the build project files in the 'projects' directory simply copy
|
|
jpayne@68
|
725 scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build
|
|
jpayne@68
|
726 systems do not permit easy auto-configuration of the library - they only
|
|
jpayne@68
|
727 support the default configuration.
|
|
jpayne@68
|
728
|
|
jpayne@68
|
729 The easiest way to make minor changes to the libpng configuration when
|
|
jpayne@68
|
730 auto-configuration is supported is to add definitions to the command line
|
|
jpayne@68
|
731 using (typically) CPPFLAGS. For example:
|
|
jpayne@68
|
732
|
|
jpayne@68
|
733 CPPFLAGS=\-DPNG_NO_FLOATING_ARITHMETIC
|
|
jpayne@68
|
734
|
|
jpayne@68
|
735 will change the internal libpng math implementation for gamma correction and
|
|
jpayne@68
|
736 other arithmetic calculations to fixed point, avoiding the need for fast
|
|
jpayne@68
|
737 floating point support. The result can be seen in the generated pnglibconf.h -
|
|
jpayne@68
|
738 make sure it contains the changed feature macro setting.
|
|
jpayne@68
|
739
|
|
jpayne@68
|
740 If you need to make more extensive configuration changes - more than one or two
|
|
jpayne@68
|
741 feature macro settings - you can either add \-DPNG_USER_CONFIG to the build
|
|
jpayne@68
|
742 command line and put a list of feature macro settings in pngusr.h or you can set
|
|
jpayne@68
|
743 DFA_XTRA (a makefile variable) to a file containing the same information in the
|
|
jpayne@68
|
744 form of 'option' settings.
|
|
jpayne@68
|
745
|
|
jpayne@68
|
746 A. Changing pnglibconf.h
|
|
jpayne@68
|
747
|
|
jpayne@68
|
748 A variety of methods exist to build libpng. Not all of these support
|
|
jpayne@68
|
749 reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be
|
|
jpayne@68
|
750 rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand.
|
|
jpayne@68
|
751
|
|
jpayne@68
|
752 Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to
|
|
jpayne@68
|
753 pnglibconf.h and changing the lines defining the supported features, paying
|
|
jpayne@68
|
754 very close attention to the 'option' information in scripts/pnglibconf.dfa
|
|
jpayne@68
|
755 that describes those features and their requirements. This is easy to get
|
|
jpayne@68
|
756 wrong.
|
|
jpayne@68
|
757
|
|
jpayne@68
|
758 B. Configuration using DFA_XTRA
|
|
jpayne@68
|
759
|
|
jpayne@68
|
760 Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later
|
|
jpayne@68
|
761 variant such as 'nawk' or 'gawk', is available. The configure build will
|
|
jpayne@68
|
762 automatically find an appropriate awk and build pnglibconf.h.
|
|
jpayne@68
|
763 The scripts/pnglibconf.mak file contains a set of make rules for doing the
|
|
jpayne@68
|
764 same thing if configure is not used, and many of the makefiles in the scripts
|
|
jpayne@68
|
765 directory use this approach.
|
|
jpayne@68
|
766
|
|
jpayne@68
|
767 When rebuilding simply write a new file containing changed options and set
|
|
jpayne@68
|
768 DFA_XTRA to the name of this file. This causes the build to append the new file
|
|
jpayne@68
|
769 to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines
|
|
jpayne@68
|
770 of the following forms:
|
|
jpayne@68
|
771
|
|
jpayne@68
|
772 everything = off
|
|
jpayne@68
|
773
|
|
jpayne@68
|
774 This turns all optional features off. Include it at the start of pngusr.dfa to
|
|
jpayne@68
|
775 make it easier to build a minimal configuration. You will need to turn at least
|
|
jpayne@68
|
776 some features on afterward to enable either reading or writing code, or both.
|
|
jpayne@68
|
777
|
|
jpayne@68
|
778 option feature on
|
|
jpayne@68
|
779 option feature off
|
|
jpayne@68
|
780
|
|
jpayne@68
|
781 Enable or disable a single feature. This will automatically enable other
|
|
jpayne@68
|
782 features required by a feature that is turned on or disable other features that
|
|
jpayne@68
|
783 require a feature which is turned off. Conflicting settings will cause an error
|
|
jpayne@68
|
784 message to be emitted by awk.
|
|
jpayne@68
|
785
|
|
jpayne@68
|
786 setting feature default value
|
|
jpayne@68
|
787
|
|
jpayne@68
|
788 Changes the default value of setting 'feature' to 'value'. There are a small
|
|
jpayne@68
|
789 number of settings listed at the top of pnglibconf.h, they are documented in the
|
|
jpayne@68
|
790 source code. Most of these values have performance implications for the library
|
|
jpayne@68
|
791 but most of them have no visible effect on the API. Some can also be overridden
|
|
jpayne@68
|
792 from the API.
|
|
jpayne@68
|
793
|
|
jpayne@68
|
794 This method of building a customized pnglibconf.h is illustrated in
|
|
jpayne@68
|
795 contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and
|
|
jpayne@68
|
796 pngusr.dfa in these directories.
|
|
jpayne@68
|
797
|
|
jpayne@68
|
798 C. Configuration using PNG_USER_CONFIG
|
|
jpayne@68
|
799
|
|
jpayne@68
|
800 If \-DPNG_USER_CONFIG is added to the CPPFLAGS when pnglibconf.h is built,
|
|
jpayne@68
|
801 the file pngusr.h will automatically be included before the options in
|
|
jpayne@68
|
802 scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only
|
|
jpayne@68
|
803 macro definitions turning features on or off or setting settings.
|
|
jpayne@68
|
804
|
|
jpayne@68
|
805 Apart from the global setting "everything = off" all the options listed above
|
|
jpayne@68
|
806 can be set using macros in pngusr.h:
|
|
jpayne@68
|
807
|
|
jpayne@68
|
808 #define PNG_feature_SUPPORTED
|
|
jpayne@68
|
809
|
|
jpayne@68
|
810 is equivalent to:
|
|
jpayne@68
|
811
|
|
jpayne@68
|
812 option feature on
|
|
jpayne@68
|
813
|
|
jpayne@68
|
814 #define PNG_NO_feature
|
|
jpayne@68
|
815
|
|
jpayne@68
|
816 is equivalent to:
|
|
jpayne@68
|
817
|
|
jpayne@68
|
818 option feature off
|
|
jpayne@68
|
819
|
|
jpayne@68
|
820 #define PNG_feature value
|
|
jpayne@68
|
821
|
|
jpayne@68
|
822 is equivalent to:
|
|
jpayne@68
|
823
|
|
jpayne@68
|
824 setting feature default value
|
|
jpayne@68
|
825
|
|
jpayne@68
|
826 Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the
|
|
jpayne@68
|
827 pngusr file you supply override the contents of scripts/pnglibconf.dfa
|
|
jpayne@68
|
828
|
|
jpayne@68
|
829 If confusing or incomprehensible behavior results it is possible to
|
|
jpayne@68
|
830 examine the intermediate file pnglibconf.dfn to find the full set of
|
|
jpayne@68
|
831 dependency information for each setting and option. Simply locate the
|
|
jpayne@68
|
832 feature in the file and read the C comments that precede it.
|
|
jpayne@68
|
833
|
|
jpayne@68
|
834 This method is also illustrated in the contrib/pngminim/* makefiles and
|
|
jpayne@68
|
835 pngusr.h.
|
|
jpayne@68
|
836
|
|
jpayne@68
|
837 .SH III. Reading
|
|
jpayne@68
|
838
|
|
jpayne@68
|
839 We'll now walk you through the possible functions to call when reading
|
|
jpayne@68
|
840 in a PNG file sequentially, briefly explaining the syntax and purpose
|
|
jpayne@68
|
841 of each one. See example.c and png.h for more detail. While
|
|
jpayne@68
|
842 progressive reading is covered in the next section, you will still
|
|
jpayne@68
|
843 need some of the functions discussed in this section to read a PNG
|
|
jpayne@68
|
844 file.
|
|
jpayne@68
|
845
|
|
jpayne@68
|
846 .SS Setup
|
|
jpayne@68
|
847
|
|
jpayne@68
|
848 You will want to do the I/O initialization(*) before you get into libpng,
|
|
jpayne@68
|
849 so if it doesn't work, you don't have much to undo. Of course, you
|
|
jpayne@68
|
850 will also want to insure that you are, in fact, dealing with a PNG
|
|
jpayne@68
|
851 file. Libpng provides a simple check to see if a file is a PNG file.
|
|
jpayne@68
|
852 To use it, pass in the first 1 to 8 bytes of the file to the function
|
|
jpayne@68
|
853 png_sig_cmp(), and it will return 0 (false) if the bytes match the
|
|
jpayne@68
|
854 corresponding bytes of the PNG signature, or nonzero (true) otherwise.
|
|
jpayne@68
|
855 Of course, the more bytes you pass in, the greater the accuracy of the
|
|
jpayne@68
|
856 prediction.
|
|
jpayne@68
|
857
|
|
jpayne@68
|
858 If you are intending to keep the file pointer open for use in libpng,
|
|
jpayne@68
|
859 you must ensure you don't read more than 8 bytes from the beginning
|
|
jpayne@68
|
860 of the file, and you also have to make a call to png_set_sig_bytes()
|
|
jpayne@68
|
861 with the number of bytes you read from the beginning. Libpng will
|
|
jpayne@68
|
862 then only check the bytes (if any) that your program didn't read.
|
|
jpayne@68
|
863
|
|
jpayne@68
|
864 (*): If you are not using the standard I/O functions, you will need
|
|
jpayne@68
|
865 to replace them with custom functions. See the discussion under
|
|
jpayne@68
|
866 Customizing libpng.
|
|
jpayne@68
|
867
|
|
jpayne@68
|
868 FILE *fp = fopen(file_name, "rb");
|
|
jpayne@68
|
869 if (!fp)
|
|
jpayne@68
|
870 {
|
|
jpayne@68
|
871 return ERROR;
|
|
jpayne@68
|
872 }
|
|
jpayne@68
|
873
|
|
jpayne@68
|
874 if (fread(header, 1, number, fp) != number)
|
|
jpayne@68
|
875 {
|
|
jpayne@68
|
876 return ERROR;
|
|
jpayne@68
|
877 }
|
|
jpayne@68
|
878
|
|
jpayne@68
|
879 is_png = (png_sig_cmp(header, 0, number) == 0);
|
|
jpayne@68
|
880 if (!is_png)
|
|
jpayne@68
|
881 {
|
|
jpayne@68
|
882 return NOT_PNG;
|
|
jpayne@68
|
883 }
|
|
jpayne@68
|
884
|
|
jpayne@68
|
885 Next, png_struct and png_info need to be allocated and initialized. In
|
|
jpayne@68
|
886 order to ensure that the size of these structures is correct even with a
|
|
jpayne@68
|
887 dynamically linked libpng, there are functions to initialize and
|
|
jpayne@68
|
888 allocate the structures. We also pass the library version, optional
|
|
jpayne@68
|
889 pointers to error handling functions, and a pointer to a data struct for
|
|
jpayne@68
|
890 use by the error functions, if necessary (the pointer and functions can
|
|
jpayne@68
|
891 be NULL if the default error handlers are to be used). See the section
|
|
jpayne@68
|
892 on Changes to Libpng below regarding the old initialization functions.
|
|
jpayne@68
|
893 The structure allocation functions quietly return NULL if they fail to
|
|
jpayne@68
|
894 create the structure, so your application should check for that.
|
|
jpayne@68
|
895
|
|
jpayne@68
|
896 png_structp png_ptr = png_create_read_struct
|
|
jpayne@68
|
897 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
jpayne@68
|
898 user_error_fn, user_warning_fn);
|
|
jpayne@68
|
899
|
|
jpayne@68
|
900 if (!png_ptr)
|
|
jpayne@68
|
901 return ERROR;
|
|
jpayne@68
|
902
|
|
jpayne@68
|
903 png_infop info_ptr = png_create_info_struct(png_ptr);
|
|
jpayne@68
|
904
|
|
jpayne@68
|
905 if (!info_ptr)
|
|
jpayne@68
|
906 {
|
|
jpayne@68
|
907 png_destroy_read_struct(&png_ptr, NULL, NULL);
|
|
jpayne@68
|
908 return ERROR;
|
|
jpayne@68
|
909 }
|
|
jpayne@68
|
910
|
|
jpayne@68
|
911 If you want to use your own memory allocation routines,
|
|
jpayne@68
|
912 use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use
|
|
jpayne@68
|
913 png_create_read_struct_2() instead of png_create_read_struct():
|
|
jpayne@68
|
914
|
|
jpayne@68
|
915 png_structp png_ptr = png_create_read_struct_2
|
|
jpayne@68
|
916 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
jpayne@68
|
917 user_error_fn, user_warning_fn, (png_voidp)
|
|
jpayne@68
|
918 user_mem_ptr, user_malloc_fn, user_free_fn);
|
|
jpayne@68
|
919
|
|
jpayne@68
|
920 The error handling routines passed to png_create_read_struct()
|
|
jpayne@68
|
921 and the memory alloc/free routines passed to png_create_struct_2()
|
|
jpayne@68
|
922 are only necessary if you are not using the libpng supplied error
|
|
jpayne@68
|
923 handling and memory alloc/free functions.
|
|
jpayne@68
|
924
|
|
jpayne@68
|
925 When libpng encounters an error, it expects to longjmp back
|
|
jpayne@68
|
926 to your routine. Therefore, you will need to call setjmp and pass
|
|
jpayne@68
|
927 your png_jmpbuf(png_ptr). If you read the file from different
|
|
jpayne@68
|
928 routines, you will need to update the longjmp buffer every time you enter
|
|
jpayne@68
|
929 a new routine that will call a png_*() function.
|
|
jpayne@68
|
930
|
|
jpayne@68
|
931 See your documentation of setjmp/longjmp for your compiler for more
|
|
jpayne@68
|
932 information on setjmp/longjmp. See the discussion on libpng error
|
|
jpayne@68
|
933 handling in the Customizing Libpng section below for more information
|
|
jpayne@68
|
934 on the libpng error handling. If an error occurs, and libpng longjmp's
|
|
jpayne@68
|
935 back to your setjmp, you will want to call png_destroy_read_struct() to
|
|
jpayne@68
|
936 free any memory.
|
|
jpayne@68
|
937
|
|
jpayne@68
|
938 if (setjmp(png_jmpbuf(png_ptr)))
|
|
jpayne@68
|
939 {
|
|
jpayne@68
|
940 png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
|
|
jpayne@68
|
941 fclose(fp);
|
|
jpayne@68
|
942 return ERROR;
|
|
jpayne@68
|
943 }
|
|
jpayne@68
|
944
|
|
jpayne@68
|
945 Pass NULL instead of &end_info if you didn't create an end_info
|
|
jpayne@68
|
946 structure.
|
|
jpayne@68
|
947
|
|
jpayne@68
|
948 If you would rather avoid the complexity of setjmp/longjmp issues,
|
|
jpayne@68
|
949 you can compile libpng with PNG_NO_SETJMP, in which case
|
|
jpayne@68
|
950 errors will result in a call to PNG_ABORT() which defaults to abort().
|
|
jpayne@68
|
951
|
|
jpayne@68
|
952 You can #define PNG_ABORT() to a function that does something
|
|
jpayne@68
|
953 more useful than abort(), as long as your function does not
|
|
jpayne@68
|
954 return.
|
|
jpayne@68
|
955
|
|
jpayne@68
|
956 Now you need to set up the input code. The default for libpng is to
|
|
jpayne@68
|
957 use the C function fread(). If you use this, you will need to pass a
|
|
jpayne@68
|
958 valid FILE * in the function png_init_io(). Be sure that the file is
|
|
jpayne@68
|
959 opened in binary mode. If you wish to handle reading data in another
|
|
jpayne@68
|
960 way, you need not call the png_init_io() function, but you must then
|
|
jpayne@68
|
961 implement the libpng I/O methods discussed in the Customizing Libpng
|
|
jpayne@68
|
962 section below.
|
|
jpayne@68
|
963
|
|
jpayne@68
|
964 png_init_io(png_ptr, fp);
|
|
jpayne@68
|
965
|
|
jpayne@68
|
966 If you had previously opened the file and read any of the signature from
|
|
jpayne@68
|
967 the beginning in order to see if this was a PNG file, you need to let
|
|
jpayne@68
|
968 libpng know that there are some bytes missing from the start of the file.
|
|
jpayne@68
|
969
|
|
jpayne@68
|
970 png_set_sig_bytes(png_ptr, number);
|
|
jpayne@68
|
971
|
|
jpayne@68
|
972 You can change the zlib compression buffer size to be used while
|
|
jpayne@68
|
973 reading compressed data with
|
|
jpayne@68
|
974
|
|
jpayne@68
|
975 png_set_compression_buffer_size(png_ptr, buffer_size);
|
|
jpayne@68
|
976
|
|
jpayne@68
|
977 where the default size is 8192 bytes. Note that the buffer size
|
|
jpayne@68
|
978 is changed immediately and the buffer is reallocated immediately,
|
|
jpayne@68
|
979 instead of setting a flag to be acted upon later.
|
|
jpayne@68
|
980
|
|
jpayne@68
|
981 If you want CRC errors to be handled in a different manner than
|
|
jpayne@68
|
982 the default, use
|
|
jpayne@68
|
983
|
|
jpayne@68
|
984 png_set_crc_action(png_ptr, crit_action, ancil_action);
|
|
jpayne@68
|
985
|
|
jpayne@68
|
986 The values for png_set_crc_action() say how libpng is to handle CRC errors in
|
|
jpayne@68
|
987 ancillary and critical chunks, and whether to use the data contained
|
|
jpayne@68
|
988 therein. Starting with libpng-1.6.26, this also governs how an ADLER32 error
|
|
jpayne@68
|
989 is handled while reading the IDAT chunk. Note that it is impossible to
|
|
jpayne@68
|
990 "discard" data in a critical chunk.
|
|
jpayne@68
|
991
|
|
jpayne@68
|
992 Choices for (int) crit_action are
|
|
jpayne@68
|
993 PNG_CRC_DEFAULT 0 error/quit
|
|
jpayne@68
|
994 PNG_CRC_ERROR_QUIT 1 error/quit
|
|
jpayne@68
|
995 PNG_CRC_WARN_USE 3 warn/use data
|
|
jpayne@68
|
996 PNG_CRC_QUIET_USE 4 quiet/use data
|
|
jpayne@68
|
997 PNG_CRC_NO_CHANGE 5 use the current value
|
|
jpayne@68
|
998
|
|
jpayne@68
|
999 Choices for (int) ancil_action are
|
|
jpayne@68
|
1000 PNG_CRC_DEFAULT 0 error/quit
|
|
jpayne@68
|
1001 PNG_CRC_ERROR_QUIT 1 error/quit
|
|
jpayne@68
|
1002 PNG_CRC_WARN_DISCARD 2 warn/discard data
|
|
jpayne@68
|
1003 PNG_CRC_WARN_USE 3 warn/use data
|
|
jpayne@68
|
1004 PNG_CRC_QUIET_USE 4 quiet/use data
|
|
jpayne@68
|
1005 PNG_CRC_NO_CHANGE 5 use the current value
|
|
jpayne@68
|
1006
|
|
jpayne@68
|
1007 When the setting for crit_action is PNG_CRC_QUIET_USE, the CRC and ADLER32
|
|
jpayne@68
|
1008 checksums are not only ignored, but they are not evaluated.
|
|
jpayne@68
|
1009
|
|
jpayne@68
|
1010 .SS Setting up callback code
|
|
jpayne@68
|
1011
|
|
jpayne@68
|
1012 You can set up a callback function to handle any unknown chunks in the
|
|
jpayne@68
|
1013 input stream. You must supply the function
|
|
jpayne@68
|
1014
|
|
jpayne@68
|
1015 read_chunk_callback(png_structp png_ptr,
|
|
jpayne@68
|
1016 png_unknown_chunkp chunk)
|
|
jpayne@68
|
1017 {
|
|
jpayne@68
|
1018 /* The unknown chunk structure contains your
|
|
jpayne@68
|
1019 chunk data, along with similar data for any other
|
|
jpayne@68
|
1020 unknown chunks: */
|
|
jpayne@68
|
1021
|
|
jpayne@68
|
1022 png_byte name[5];
|
|
jpayne@68
|
1023 png_byte *data;
|
|
jpayne@68
|
1024 size_t size;
|
|
jpayne@68
|
1025
|
|
jpayne@68
|
1026 /* Note that libpng has already taken care of
|
|
jpayne@68
|
1027 the CRC handling */
|
|
jpayne@68
|
1028
|
|
jpayne@68
|
1029 /* put your code here. Search for your chunk in the
|
|
jpayne@68
|
1030 unknown chunk structure, process it, and return one
|
|
jpayne@68
|
1031 of the following: */
|
|
jpayne@68
|
1032
|
|
jpayne@68
|
1033 return \-n; /* chunk had an error */
|
|
jpayne@68
|
1034 return 0; /* did not recognize */
|
|
jpayne@68
|
1035 return n; /* success */
|
|
jpayne@68
|
1036 }
|
|
jpayne@68
|
1037
|
|
jpayne@68
|
1038 (You can give your function another name that you like instead of
|
|
jpayne@68
|
1039 "read_chunk_callback")
|
|
jpayne@68
|
1040
|
|
jpayne@68
|
1041 To inform libpng about your function, use
|
|
jpayne@68
|
1042
|
|
jpayne@68
|
1043 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
|
|
jpayne@68
|
1044 read_chunk_callback);
|
|
jpayne@68
|
1045
|
|
jpayne@68
|
1046 This names not only the callback function, but also a user pointer that
|
|
jpayne@68
|
1047 you can retrieve with
|
|
jpayne@68
|
1048
|
|
jpayne@68
|
1049 png_get_user_chunk_ptr(png_ptr);
|
|
jpayne@68
|
1050
|
|
jpayne@68
|
1051 If you call the png_set_read_user_chunk_fn() function, then all unknown
|
|
jpayne@68
|
1052 chunks which the callback does not handle will be saved when read. You can
|
|
jpayne@68
|
1053 cause them to be discarded by returning '1' ("handled") instead of '0'. This
|
|
jpayne@68
|
1054 behavior will change in libpng 1.7 and the default handling set by the
|
|
jpayne@68
|
1055 png_set_keep_unknown_chunks() function, described below, will be used when the
|
|
jpayne@68
|
1056 callback returns 0. If you want the existing behavior you should set the global
|
|
jpayne@68
|
1057 default to PNG_HANDLE_CHUNK_IF_SAFE now; this is compatible with all current
|
|
jpayne@68
|
1058 versions of libpng and with 1.7. Libpng 1.6 issues a warning if you keep the
|
|
jpayne@68
|
1059 default, or PNG_HANDLE_CHUNK_NEVER, and the callback returns 0.
|
|
jpayne@68
|
1060
|
|
jpayne@68
|
1061 At this point, you can set up a callback function that will be
|
|
jpayne@68
|
1062 called after each row has been read, which you can use to control
|
|
jpayne@68
|
1063 a progress meter or the like. It's demonstrated in pngtest.c.
|
|
jpayne@68
|
1064 You must supply a function
|
|
jpayne@68
|
1065
|
|
jpayne@68
|
1066 void read_row_callback(png_structp png_ptr,
|
|
jpayne@68
|
1067 png_uint_32 row, int pass)
|
|
jpayne@68
|
1068 {
|
|
jpayne@68
|
1069 /* put your code here */
|
|
jpayne@68
|
1070 }
|
|
jpayne@68
|
1071
|
|
jpayne@68
|
1072 (You can give it another name that you like instead of "read_row_callback")
|
|
jpayne@68
|
1073
|
|
jpayne@68
|
1074 To inform libpng about your function, use
|
|
jpayne@68
|
1075
|
|
jpayne@68
|
1076 png_set_read_status_fn(png_ptr, read_row_callback);
|
|
jpayne@68
|
1077
|
|
jpayne@68
|
1078 When this function is called the row has already been completely processed and
|
|
jpayne@68
|
1079 the 'row' and 'pass' refer to the next row to be handled. For the
|
|
jpayne@68
|
1080 non-interlaced case the row that was just handled is simply one less than the
|
|
jpayne@68
|
1081 passed in row number, and pass will always be 0. For the interlaced case the
|
|
jpayne@68
|
1082 same applies unless the row value is 0, in which case the row just handled was
|
|
jpayne@68
|
1083 the last one from one of the preceding passes. Because interlacing may skip a
|
|
jpayne@68
|
1084 pass you cannot be sure that the preceding pass is just 'pass\-1'; if you really
|
|
jpayne@68
|
1085 need to know what the last pass is record (row,pass) from the callback and use
|
|
jpayne@68
|
1086 the last recorded value each time.
|
|
jpayne@68
|
1087
|
|
jpayne@68
|
1088 As with the user transform you can find the output row using the
|
|
jpayne@68
|
1089 PNG_ROW_FROM_PASS_ROW macro.
|
|
jpayne@68
|
1090
|
|
jpayne@68
|
1091 .SS Unknown-chunk handling
|
|
jpayne@68
|
1092
|
|
jpayne@68
|
1093 Now you get to set the way the library processes unknown chunks in the
|
|
jpayne@68
|
1094 input PNG stream. Both known and unknown chunks will be read. Normal
|
|
jpayne@68
|
1095 behavior is that known chunks will be parsed into information in
|
|
jpayne@68
|
1096 various info_ptr members while unknown chunks will be discarded. This
|
|
jpayne@68
|
1097 behavior can be wasteful if your application will never use some known
|
|
jpayne@68
|
1098 chunk types. To change this, you can call:
|
|
jpayne@68
|
1099
|
|
jpayne@68
|
1100 png_set_keep_unknown_chunks(png_ptr, keep,
|
|
jpayne@68
|
1101 chunk_list, num_chunks);
|
|
jpayne@68
|
1102
|
|
jpayne@68
|
1103 keep - 0: default unknown chunk handling
|
|
jpayne@68
|
1104 1: ignore; do not keep
|
|
jpayne@68
|
1105 2: keep only if safe-to-copy
|
|
jpayne@68
|
1106 3: keep even if unsafe-to-copy
|
|
jpayne@68
|
1107
|
|
jpayne@68
|
1108 You can use these definitions:
|
|
jpayne@68
|
1109 PNG_HANDLE_CHUNK_AS_DEFAULT 0
|
|
jpayne@68
|
1110 PNG_HANDLE_CHUNK_NEVER 1
|
|
jpayne@68
|
1111 PNG_HANDLE_CHUNK_IF_SAFE 2
|
|
jpayne@68
|
1112 PNG_HANDLE_CHUNK_ALWAYS 3
|
|
jpayne@68
|
1113
|
|
jpayne@68
|
1114 chunk_list - list of chunks affected (a byte string,
|
|
jpayne@68
|
1115 five bytes per chunk, NULL or '\0' if
|
|
jpayne@68
|
1116 num_chunks is positive; ignored if
|
|
jpayne@68
|
1117 numchunks <= 0).
|
|
jpayne@68
|
1118
|
|
jpayne@68
|
1119 num_chunks - number of chunks affected; if 0, all
|
|
jpayne@68
|
1120 unknown chunks are affected. If positive,
|
|
jpayne@68
|
1121 only the chunks in the list are affected,
|
|
jpayne@68
|
1122 and if negative all unknown chunks and
|
|
jpayne@68
|
1123 all known chunks except for the IHDR,
|
|
jpayne@68
|
1124 PLTE, tRNS, IDAT, and IEND chunks are
|
|
jpayne@68
|
1125 affected.
|
|
jpayne@68
|
1126
|
|
jpayne@68
|
1127 Unknown chunks declared in this way will be saved as raw data onto a
|
|
jpayne@68
|
1128 list of png_unknown_chunk structures. If a chunk that is normally
|
|
jpayne@68
|
1129 known to libpng is named in the list, it will be handled as unknown,
|
|
jpayne@68
|
1130 according to the "keep" directive. If a chunk is named in successive
|
|
jpayne@68
|
1131 instances of png_set_keep_unknown_chunks(), the final instance will
|
|
jpayne@68
|
1132 take precedence. The IHDR and IEND chunks should not be named in
|
|
jpayne@68
|
1133 chunk_list; if they are, libpng will process them normally anyway.
|
|
jpayne@68
|
1134 If you know that your application will never make use of some particular
|
|
jpayne@68
|
1135 chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below.
|
|
jpayne@68
|
1136
|
|
jpayne@68
|
1137 Here is an example of the usage of png_set_keep_unknown_chunks(),
|
|
jpayne@68
|
1138 where the private "vpAg" chunk will later be processed by a user chunk
|
|
jpayne@68
|
1139 callback function:
|
|
jpayne@68
|
1140
|
|
jpayne@68
|
1141 png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
|
|
jpayne@68
|
1142
|
|
jpayne@68
|
1143 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
|
|
jpayne@68
|
1144 png_byte unused_chunks[]=
|
|
jpayne@68
|
1145 {
|
|
jpayne@68
|
1146 104, 73, 83, 84, (png_byte) '\0', /* hIST */
|
|
jpayne@68
|
1147 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
|
|
jpayne@68
|
1148 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
|
|
jpayne@68
|
1149 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
|
|
jpayne@68
|
1150 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
|
|
jpayne@68
|
1151 116, 73, 77, 69, (png_byte) '\0', /* tIME */
|
|
jpayne@68
|
1152 };
|
|
jpayne@68
|
1153 #endif
|
|
jpayne@68
|
1154
|
|
jpayne@68
|
1155 ...
|
|
jpayne@68
|
1156
|
|
jpayne@68
|
1157 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
|
|
jpayne@68
|
1158 /* ignore all unknown chunks
|
|
jpayne@68
|
1159 * (use global setting "2" for libpng16 and earlier):
|
|
jpayne@68
|
1160 */
|
|
jpayne@68
|
1161 png_set_keep_unknown_chunks(read_ptr, 2, NULL, 0);
|
|
jpayne@68
|
1162
|
|
jpayne@68
|
1163 /* except for vpAg: */
|
|
jpayne@68
|
1164 png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
|
|
jpayne@68
|
1165
|
|
jpayne@68
|
1166 /* also ignore unused known chunks: */
|
|
jpayne@68
|
1167 png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
|
|
jpayne@68
|
1168 (int)(sizeof unused_chunks)/5);
|
|
jpayne@68
|
1169 #endif
|
|
jpayne@68
|
1170
|
|
jpayne@68
|
1171 .SS User limits
|
|
jpayne@68
|
1172
|
|
jpayne@68
|
1173 The PNG specification allows the width and height of an image to be as
|
|
jpayne@68
|
1174 large as 2^(31\-1 (0x7fffffff), or about 2.147 billion rows and columns.
|
|
jpayne@68
|
1175 For safety, libpng imposes a default limit of 1 million rows and columns.
|
|
jpayne@68
|
1176 Larger images will be rejected immediately with a png_error() call. If
|
|
jpayne@68
|
1177 you wish to change these limits, you can use
|
|
jpayne@68
|
1178
|
|
jpayne@68
|
1179 png_set_user_limits(png_ptr, width_max, height_max);
|
|
jpayne@68
|
1180
|
|
jpayne@68
|
1181 to set your own limits (libpng may reject some very wide images
|
|
jpayne@68
|
1182 anyway because of potential buffer overflow conditions).
|
|
jpayne@68
|
1183
|
|
jpayne@68
|
1184 You should put this statement after you create the PNG structure and
|
|
jpayne@68
|
1185 before calling png_read_info(), png_read_png(), or png_process_data().
|
|
jpayne@68
|
1186
|
|
jpayne@68
|
1187 When writing a PNG datastream, put this statement before calling
|
|
jpayne@68
|
1188 png_write_info() or png_write_png().
|
|
jpayne@68
|
1189
|
|
jpayne@68
|
1190 If you need to retrieve the limits that are being applied, use
|
|
jpayne@68
|
1191
|
|
jpayne@68
|
1192 width_max = png_get_user_width_max(png_ptr);
|
|
jpayne@68
|
1193 height_max = png_get_user_height_max(png_ptr);
|
|
jpayne@68
|
1194
|
|
jpayne@68
|
1195 The PNG specification sets no limit on the number of ancillary chunks
|
|
jpayne@68
|
1196 allowed in a PNG datastream. By default, libpng imposes a limit of
|
|
jpayne@68
|
1197 a total of 1000 sPLT, tEXt, iTXt, zTXt, and unknown chunks to be stored.
|
|
jpayne@68
|
1198 If you have set up both info_ptr and end_info_ptr, the limit applies
|
|
jpayne@68
|
1199 separately to each. You can change the limit on the total number of such
|
|
jpayne@68
|
1200 chunks that will be stored, with
|
|
jpayne@68
|
1201
|
|
jpayne@68
|
1202 png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
|
|
jpayne@68
|
1203
|
|
jpayne@68
|
1204 where 0x7fffffffL means unlimited. You can retrieve this limit with
|
|
jpayne@68
|
1205
|
|
jpayne@68
|
1206 chunk_cache_max = png_get_chunk_cache_max(png_ptr);
|
|
jpayne@68
|
1207
|
|
jpayne@68
|
1208 Libpng imposes a limit of 8 Megabytes (8,000,000 bytes) on the amount of
|
|
jpayne@68
|
1209 memory that any chunk other than IDAT can occupy, originally or when
|
|
jpayne@68
|
1210 decompressed (prior to libpng-1.6.32 the limit was only applied to compressed
|
|
jpayne@68
|
1211 chunks after decompression). You can change this limit with
|
|
jpayne@68
|
1212
|
|
jpayne@68
|
1213 png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
|
|
jpayne@68
|
1214
|
|
jpayne@68
|
1215 and you can retrieve the limit with
|
|
jpayne@68
|
1216
|
|
jpayne@68
|
1217 chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
|
|
jpayne@68
|
1218
|
|
jpayne@68
|
1219 Any chunks that would cause either of these limits to be exceeded will
|
|
jpayne@68
|
1220 be ignored.
|
|
jpayne@68
|
1221
|
|
jpayne@68
|
1222 .SS Information about your system
|
|
jpayne@68
|
1223
|
|
jpayne@68
|
1224 If you intend to display the PNG or to incorporate it in other image data you
|
|
jpayne@68
|
1225 need to tell libpng information about your display or drawing surface so that
|
|
jpayne@68
|
1226 libpng can convert the values in the image to match the display.
|
|
jpayne@68
|
1227
|
|
jpayne@68
|
1228 From libpng-1.5.4 this information can be set before reading the PNG file
|
|
jpayne@68
|
1229 header. In earlier versions png_set_gamma() existed but behaved incorrectly if
|
|
jpayne@68
|
1230 called before the PNG file header had been read and png_set_alpha_mode() did not
|
|
jpayne@68
|
1231 exist.
|
|
jpayne@68
|
1232
|
|
jpayne@68
|
1233 If you need to support versions prior to libpng-1.5.4 test the version number
|
|
jpayne@68
|
1234 as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures
|
|
jpayne@68
|
1235 described in the appropriate manual page.
|
|
jpayne@68
|
1236
|
|
jpayne@68
|
1237 You give libpng the encoding expected by your system expressed as a 'gamma'
|
|
jpayne@68
|
1238 value. You can also specify a default encoding for the PNG file in
|
|
jpayne@68
|
1239 case the required information is missing from the file. By default libpng
|
|
jpayne@68
|
1240 assumes that the PNG data matches your system, to keep this default call:
|
|
jpayne@68
|
1241
|
|
jpayne@68
|
1242 png_set_gamma(png_ptr, screen_gamma, output_gamma);
|
|
jpayne@68
|
1243
|
|
jpayne@68
|
1244 or you can use the fixed point equivalent:
|
|
jpayne@68
|
1245
|
|
jpayne@68
|
1246 png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma,
|
|
jpayne@68
|
1247 PNG_FP_1*output_gamma);
|
|
jpayne@68
|
1248
|
|
jpayne@68
|
1249 If you don't know the gamma for your system it is probably 2.2 - a good
|
|
jpayne@68
|
1250 approximation to the IEC standard for display systems (sRGB). If images are
|
|
jpayne@68
|
1251 too contrasty or washed out you got the value wrong - check your system
|
|
jpayne@68
|
1252 documentation!
|
|
jpayne@68
|
1253
|
|
jpayne@68
|
1254 Many systems permit the system gamma to be changed via a lookup table in the
|
|
jpayne@68
|
1255 display driver, a few systems, including older Macs, change the response by
|
|
jpayne@68
|
1256 default. As of 1.5.4 three special values are available to handle common
|
|
jpayne@68
|
1257 situations:
|
|
jpayne@68
|
1258
|
|
jpayne@68
|
1259 PNG_DEFAULT_sRGB: Indicates that the system conforms to the
|
|
jpayne@68
|
1260 IEC 61966-2-1 standard. This matches almost
|
|
jpayne@68
|
1261 all systems.
|
|
jpayne@68
|
1262 PNG_GAMMA_MAC_18: Indicates that the system is an older
|
|
jpayne@68
|
1263 (pre Mac OS 10.6) Apple Macintosh system with
|
|
jpayne@68
|
1264 the default settings.
|
|
jpayne@68
|
1265 PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates
|
|
jpayne@68
|
1266 that the system expects data with no gamma
|
|
jpayne@68
|
1267 encoding.
|
|
jpayne@68
|
1268
|
|
jpayne@68
|
1269 You would use the linear (unencoded) value if you need to process the pixel
|
|
jpayne@68
|
1270 values further because this avoids the need to decode and re-encode each
|
|
jpayne@68
|
1271 component value whenever arithmetic is performed. A lot of graphics software
|
|
jpayne@68
|
1272 uses linear values for this reason, often with higher precision component values
|
|
jpayne@68
|
1273 to preserve overall accuracy.
|
|
jpayne@68
|
1274
|
|
jpayne@68
|
1275
|
|
jpayne@68
|
1276 The output_gamma value expresses how to decode the output values, not how
|
|
jpayne@68
|
1277 they are encoded. The values used correspond to the normal numbers used to
|
|
jpayne@68
|
1278 describe the overall gamma of a computer display system; for example 2.2 for
|
|
jpayne@68
|
1279 an sRGB conformant system. The values are scaled by 100000 in the _fixed
|
|
jpayne@68
|
1280 version of the API (so 220000 for sRGB.)
|
|
jpayne@68
|
1281
|
|
jpayne@68
|
1282 The inverse of the value is always used to provide a default for the PNG file
|
|
jpayne@68
|
1283 encoding if it has no gAMA chunk and if png_set_gamma() has not been called
|
|
jpayne@68
|
1284 to override the PNG gamma information.
|
|
jpayne@68
|
1285
|
|
jpayne@68
|
1286 When the ALPHA_OPTIMIZED mode is selected the output gamma is used to encode
|
|
jpayne@68
|
1287 opaque pixels however pixels with lower alpha values are not encoded,
|
|
jpayne@68
|
1288 regardless of the output gamma setting.
|
|
jpayne@68
|
1289
|
|
jpayne@68
|
1290 When the standard Porter Duff handling is requested with mode 1 the output
|
|
jpayne@68
|
1291 encoding is set to be linear and the output_gamma value is only relevant
|
|
jpayne@68
|
1292 as a default for input data that has no gamma information. The linear output
|
|
jpayne@68
|
1293 encoding will be overridden if png_set_gamma() is called - the results may be
|
|
jpayne@68
|
1294 highly unexpected!
|
|
jpayne@68
|
1295
|
|
jpayne@68
|
1296 The following numbers are derived from the sRGB standard and the research
|
|
jpayne@68
|
1297 behind it. sRGB is defined to be approximated by a PNG gAMA chunk value of
|
|
jpayne@68
|
1298 0.45455 (1/2.2) for PNG. The value implicitly includes any viewing
|
|
jpayne@68
|
1299 correction required to take account of any differences in the color
|
|
jpayne@68
|
1300 environment of the original scene and the intended display environment; the
|
|
jpayne@68
|
1301 value expresses how to *decode* the image for display, not how the original
|
|
jpayne@68
|
1302 data was *encoded*.
|
|
jpayne@68
|
1303
|
|
jpayne@68
|
1304 sRGB provides a peg for the PNG standard by defining a viewing environment.
|
|
jpayne@68
|
1305 sRGB itself, and earlier TV standards, actually use a more complex transform
|
|
jpayne@68
|
1306 (a linear portion then a gamma 2.4 power law) than PNG can express. (PNG is
|
|
jpayne@68
|
1307 limited to simple power laws.) By saying that an image for direct display on
|
|
jpayne@68
|
1308 an sRGB conformant system should be stored with a gAMA chunk value of 45455
|
|
jpayne@68
|
1309 (11.3.3.2 and 11.3.3.5 of the ISO PNG specification) the PNG specification
|
|
jpayne@68
|
1310 makes it possible to derive values for other display systems and
|
|
jpayne@68
|
1311 environments.
|
|
jpayne@68
|
1312
|
|
jpayne@68
|
1313 The Mac value is deduced from the sRGB based on an assumption that the actual
|
|
jpayne@68
|
1314 extra viewing correction used in early Mac display systems was implemented as
|
|
jpayne@68
|
1315 a power 1.45 lookup table.
|
|
jpayne@68
|
1316
|
|
jpayne@68
|
1317 Any system where a programmable lookup table is used or where the behavior of
|
|
jpayne@68
|
1318 the final display device characteristics can be changed requires system
|
|
jpayne@68
|
1319 specific code to obtain the current characteristic. However this can be
|
|
jpayne@68
|
1320 difficult and most PNG gamma correction only requires an approximate value.
|
|
jpayne@68
|
1321
|
|
jpayne@68
|
1322 By default, if png_set_alpha_mode() is not called, libpng assumes that all
|
|
jpayne@68
|
1323 values are unencoded, linear, values and that the output device also has a
|
|
jpayne@68
|
1324 linear characteristic. This is only very rarely correct - it is invariably
|
|
jpayne@68
|
1325 better to call png_set_alpha_mode() with PNG_DEFAULT_sRGB than rely on the
|
|
jpayne@68
|
1326 default if you don't know what the right answer is!
|
|
jpayne@68
|
1327
|
|
jpayne@68
|
1328 The special value PNG_GAMMA_MAC_18 indicates an older Mac system (pre Mac OS
|
|
jpayne@68
|
1329 10.6) which used a correction table to implement a somewhat lower gamma on an
|
|
jpayne@68
|
1330 otherwise sRGB system.
|
|
jpayne@68
|
1331
|
|
jpayne@68
|
1332 Both these values are reserved (not simple gamma values) in order to allow
|
|
jpayne@68
|
1333 more precise correction internally in the future.
|
|
jpayne@68
|
1334
|
|
jpayne@68
|
1335 NOTE: the values can be passed to either the fixed or floating
|
|
jpayne@68
|
1336 point APIs, but the floating point API will also accept floating point
|
|
jpayne@68
|
1337 values.
|
|
jpayne@68
|
1338
|
|
jpayne@68
|
1339 The second thing you may need to tell libpng about is how your system handles
|
|
jpayne@68
|
1340 alpha channel information. Some, but not all, PNG files contain an alpha
|
|
jpayne@68
|
1341 channel. To display these files correctly you need to compose the data onto a
|
|
jpayne@68
|
1342 suitable background, as described in the PNG specification.
|
|
jpayne@68
|
1343
|
|
jpayne@68
|
1344 Libpng only supports composing onto a single color (using png_set_background;
|
|
jpayne@68
|
1345 see below). Otherwise you must do the composition yourself and, in this case,
|
|
jpayne@68
|
1346 you may need to call png_set_alpha_mode:
|
|
jpayne@68
|
1347
|
|
jpayne@68
|
1348 #if PNG_LIBPNG_VER >= 10504
|
|
jpayne@68
|
1349 png_set_alpha_mode(png_ptr, mode, screen_gamma);
|
|
jpayne@68
|
1350 #else
|
|
jpayne@68
|
1351 png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma);
|
|
jpayne@68
|
1352 #endif
|
|
jpayne@68
|
1353
|
|
jpayne@68
|
1354 The screen_gamma value is the same as the argument to png_set_gamma; however,
|
|
jpayne@68
|
1355 how it affects the output depends on the mode. png_set_alpha_mode() sets the
|
|
jpayne@68
|
1356 file gamma default to 1/screen_gamma, so normally you don't need to call
|
|
jpayne@68
|
1357 png_set_gamma. If you need different defaults call png_set_gamma() before
|
|
jpayne@68
|
1358 png_set_alpha_mode() - if you call it after it will override the settings made
|
|
jpayne@68
|
1359 by png_set_alpha_mode().
|
|
jpayne@68
|
1360
|
|
jpayne@68
|
1361 The mode is as follows:
|
|
jpayne@68
|
1362
|
|
jpayne@68
|
1363 PNG_ALPHA_PNG: The data is encoded according to the PNG
|
|
jpayne@68
|
1364 specification. Red, green and blue, or gray, components are
|
|
jpayne@68
|
1365 gamma encoded color values and are not premultiplied by the
|
|
jpayne@68
|
1366 alpha value. The alpha value is a linear measure of the
|
|
jpayne@68
|
1367 contribution of the pixel to the corresponding final output pixel.
|
|
jpayne@68
|
1368
|
|
jpayne@68
|
1369 You should normally use this format if you intend to perform
|
|
jpayne@68
|
1370 color correction on the color values; most, maybe all, color
|
|
jpayne@68
|
1371 correction software has no handling for the alpha channel and,
|
|
jpayne@68
|
1372 anyway, the math to handle pre-multiplied component values is
|
|
jpayne@68
|
1373 unnecessarily complex.
|
|
jpayne@68
|
1374
|
|
jpayne@68
|
1375 Before you do any arithmetic on the component values you need
|
|
jpayne@68
|
1376 to remove the gamma encoding and multiply out the alpha
|
|
jpayne@68
|
1377 channel. See the PNG specification for more detail. It is
|
|
jpayne@68
|
1378 important to note that when an image with an alpha channel is
|
|
jpayne@68
|
1379 scaled, linear encoded, pre-multiplied component values must
|
|
jpayne@68
|
1380 be used!
|
|
jpayne@68
|
1381
|
|
jpayne@68
|
1382 The remaining modes assume you don't need to do any further color correction or
|
|
jpayne@68
|
1383 that if you do, your color correction software knows all about alpha (it
|
|
jpayne@68
|
1384 probably doesn't!). They 'associate' the alpha with the color information by
|
|
jpayne@68
|
1385 storing color channel values that have been scaled by the alpha. The
|
|
jpayne@68
|
1386 advantage is that the color channels can be resampled (the image can be
|
|
jpayne@68
|
1387 scaled) in this form. The disadvantage is that normal practice is to store
|
|
jpayne@68
|
1388 linear, not (gamma) encoded, values and this requires 16-bit channels for
|
|
jpayne@68
|
1389 still images rather than the 8-bit channels that are just about sufficient if
|
|
jpayne@68
|
1390 gamma encoding is used. In addition all non-transparent pixel values,
|
|
jpayne@68
|
1391 including completely opaque ones, must be gamma encoded to produce the final
|
|
jpayne@68
|
1392 image. These are the 'STANDARD', 'ASSOCIATED' or 'PREMULTIPLIED' modes
|
|
jpayne@68
|
1393 described below (the latter being the two common names for associated alpha
|
|
jpayne@68
|
1394 color channels). Note that PNG files always contain non-associated color
|
|
jpayne@68
|
1395 channels; png_set_alpha_mode() with one of the modes causes the decoder to
|
|
jpayne@68
|
1396 convert the pixels to an associated form before returning them to your
|
|
jpayne@68
|
1397 application.
|
|
jpayne@68
|
1398
|
|
jpayne@68
|
1399 Since it is not necessary to perform arithmetic on opaque color values so
|
|
jpayne@68
|
1400 long as they are not to be resampled and are in the final color space it is
|
|
jpayne@68
|
1401 possible to optimize the handling of alpha by storing the opaque pixels in
|
|
jpayne@68
|
1402 the PNG format (adjusted for the output color space) while storing partially
|
|
jpayne@68
|
1403 opaque pixels in the standard, linear, format. The accuracy required for
|
|
jpayne@68
|
1404 standard alpha composition is relatively low, because the pixels are
|
|
jpayne@68
|
1405 isolated, therefore typically the accuracy loss in storing 8-bit linear
|
|
jpayne@68
|
1406 values is acceptable. (This is not true if the alpha channel is used to
|
|
jpayne@68
|
1407 simulate transparency over large areas - use 16 bits or the PNG mode in
|
|
jpayne@68
|
1408 this case!) This is the 'OPTIMIZED' mode. For this mode a pixel is
|
|
jpayne@68
|
1409 treated as opaque only if the alpha value is equal to the maximum value.
|
|
jpayne@68
|
1410
|
|
jpayne@68
|
1411 PNG_ALPHA_STANDARD: The data libpng produces is encoded in the
|
|
jpayne@68
|
1412 standard way assumed by most correctly written graphics software.
|
|
jpayne@68
|
1413 The gamma encoding will be removed by libpng and the
|
|
jpayne@68
|
1414 linear component values will be pre-multiplied by the
|
|
jpayne@68
|
1415 alpha channel.
|
|
jpayne@68
|
1416
|
|
jpayne@68
|
1417 With this format the final image must be re-encoded to
|
|
jpayne@68
|
1418 match the display gamma before the image is displayed.
|
|
jpayne@68
|
1419 If your system doesn't do that, yet still seems to
|
|
jpayne@68
|
1420 perform arithmetic on the pixels without decoding them,
|
|
jpayne@68
|
1421 it is broken - check out the modes below.
|
|
jpayne@68
|
1422
|
|
jpayne@68
|
1423 With PNG_ALPHA_STANDARD libpng always produces linear
|
|
jpayne@68
|
1424 component values, whatever screen_gamma you supply. The
|
|
jpayne@68
|
1425 screen_gamma value is, however, used as a default for
|
|
jpayne@68
|
1426 the file gamma if the PNG file has no gamma information.
|
|
jpayne@68
|
1427
|
|
jpayne@68
|
1428 If you call png_set_gamma() after png_set_alpha_mode() you
|
|
jpayne@68
|
1429 will override the linear encoding. Instead the
|
|
jpayne@68
|
1430 pre-multiplied pixel values will be gamma encoded but
|
|
jpayne@68
|
1431 the alpha channel will still be linear. This may
|
|
jpayne@68
|
1432 actually match the requirements of some broken software,
|
|
jpayne@68
|
1433 but it is unlikely.
|
|
jpayne@68
|
1434
|
|
jpayne@68
|
1435 While linear 8-bit data is often used it has
|
|
jpayne@68
|
1436 insufficient precision for any image with a reasonable
|
|
jpayne@68
|
1437 dynamic range. To avoid problems, and if your software
|
|
jpayne@68
|
1438 supports it, use png_set_expand_16() to force all
|
|
jpayne@68
|
1439 components to 16 bits.
|
|
jpayne@68
|
1440
|
|
jpayne@68
|
1441 PNG_ALPHA_OPTIMIZED: This mode is the same as PNG_ALPHA_STANDARD
|
|
jpayne@68
|
1442 except that completely opaque pixels are gamma encoded according to
|
|
jpayne@68
|
1443 the screen_gamma value. Pixels with alpha less than 1.0
|
|
jpayne@68
|
1444 will still have linear components.
|
|
jpayne@68
|
1445
|
|
jpayne@68
|
1446 Use this format if you have control over your
|
|
jpayne@68
|
1447 compositing software and so don't do other arithmetic
|
|
jpayne@68
|
1448 (such as scaling) on the data you get from libpng. Your
|
|
jpayne@68
|
1449 compositing software can simply copy opaque pixels to
|
|
jpayne@68
|
1450 the output but still has linear values for the
|
|
jpayne@68
|
1451 non-opaque pixels.
|
|
jpayne@68
|
1452
|
|
jpayne@68
|
1453 In normal compositing, where the alpha channel encodes
|
|
jpayne@68
|
1454 partial pixel coverage (as opposed to broad area
|
|
jpayne@68
|
1455 translucency), the inaccuracies of the 8-bit
|
|
jpayne@68
|
1456 representation of non-opaque pixels are irrelevant.
|
|
jpayne@68
|
1457
|
|
jpayne@68
|
1458 You can also try this format if your software is broken;
|
|
jpayne@68
|
1459 it might look better.
|
|
jpayne@68
|
1460
|
|
jpayne@68
|
1461 PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD; however, all component
|
|
jpayne@68
|
1462 values, including the alpha channel are gamma encoded. This is
|
|
jpayne@68
|
1463 broken because, in practice, no implementation that uses this choice
|
|
jpayne@68
|
1464 correctly undoes the encoding before handling alpha composition. Use this
|
|
jpayne@68
|
1465 choice only if other serious errors in the software or hardware you use
|
|
jpayne@68
|
1466 mandate it. In most cases of broken software or hardware the bug in the
|
|
jpayne@68
|
1467 final display manifests as a subtle halo around composited parts of the
|
|
jpayne@68
|
1468 image. You may not even perceive this as a halo; the composited part of
|
|
jpayne@68
|
1469 the image may simply appear separate from the background, as though it had
|
|
jpayne@68
|
1470 been cut out of paper and pasted on afterward.
|
|
jpayne@68
|
1471
|
|
jpayne@68
|
1472 If you don't have to deal with bugs in software or hardware, or if you can fix
|
|
jpayne@68
|
1473 them, there are three recommended ways of using png_set_alpha_mode():
|
|
jpayne@68
|
1474
|
|
jpayne@68
|
1475 png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG,
|
|
jpayne@68
|
1476 screen_gamma);
|
|
jpayne@68
|
1477
|
|
jpayne@68
|
1478 You can do color correction on the result (libpng does not currently
|
|
jpayne@68
|
1479 support color correction internally). When you handle the alpha channel
|
|
jpayne@68
|
1480 you need to undo the gamma encoding and multiply out the alpha.
|
|
jpayne@68
|
1481
|
|
jpayne@68
|
1482 png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD,
|
|
jpayne@68
|
1483 screen_gamma);
|
|
jpayne@68
|
1484 png_set_expand_16(png_ptr);
|
|
jpayne@68
|
1485
|
|
jpayne@68
|
1486 If you are using the high level interface, don't call png_set_expand_16();
|
|
jpayne@68
|
1487 instead pass PNG_TRANSFORM_EXPAND_16 to the interface.
|
|
jpayne@68
|
1488
|
|
jpayne@68
|
1489 With this mode you can't do color correction, but you can do arithmetic,
|
|
jpayne@68
|
1490 including composition and scaling, on the data without further processing.
|
|
jpayne@68
|
1491
|
|
jpayne@68
|
1492 png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED,
|
|
jpayne@68
|
1493 screen_gamma);
|
|
jpayne@68
|
1494
|
|
jpayne@68
|
1495 You can avoid the expansion to 16-bit components with this mode, but you
|
|
jpayne@68
|
1496 lose the ability to scale the image or perform other linear arithmetic.
|
|
jpayne@68
|
1497 All you can do is compose the result onto a matching output. Since this
|
|
jpayne@68
|
1498 mode is libpng-specific you also need to write your own composition
|
|
jpayne@68
|
1499 software.
|
|
jpayne@68
|
1500
|
|
jpayne@68
|
1501 The following are examples of calls to png_set_alpha_mode to achieve the
|
|
jpayne@68
|
1502 required overall gamma correction and, where necessary, alpha
|
|
jpayne@68
|
1503 premultiplication.
|
|
jpayne@68
|
1504
|
|
jpayne@68
|
1505 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
|
|
jpayne@68
|
1506
|
|
jpayne@68
|
1507 Choices for the alpha_mode are
|
|
jpayne@68
|
1508
|
|
jpayne@68
|
1509 PNG_ALPHA_PNG 0 /* according to the PNG standard */
|
|
jpayne@68
|
1510 PNG_ALPHA_STANDARD 1 /* according to Porter/Duff */
|
|
jpayne@68
|
1511 PNG_ALPHA_ASSOCIATED 1 /* as above; this is the normal practice */
|
|
jpayne@68
|
1512 PNG_ALPHA_PREMULTIPLIED 1 /* as above */
|
|
jpayne@68
|
1513 PNG_ALPHA_OPTIMIZED 2 /* 'PNG' for opaque pixels, else 'STANDARD' */
|
|
jpayne@68
|
1514 PNG_ALPHA_BROKEN 3 /* the alpha channel is gamma encoded */
|
|
jpayne@68
|
1515
|
|
jpayne@68
|
1516 PNG_ALPHA_PNG is the default libpng handling of the alpha channel. It is not
|
|
jpayne@68
|
1517 pre-multiplied into the color components. In addition the call states
|
|
jpayne@68
|
1518 that the output is for a sRGB system and causes all PNG files without gAMA
|
|
jpayne@68
|
1519 chunks to be assumed to be encoded using sRGB.
|
|
jpayne@68
|
1520
|
|
jpayne@68
|
1521 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC);
|
|
jpayne@68
|
1522
|
|
jpayne@68
|
1523 In this case the output is assumed to be something like an sRGB conformant
|
|
jpayne@68
|
1524 display preceded by a power-law lookup table of power 1.45. This is how
|
|
jpayne@68
|
1525 early Mac systems behaved.
|
|
jpayne@68
|
1526
|
|
jpayne@68
|
1527 png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_GAMMA_LINEAR);
|
|
jpayne@68
|
1528
|
|
jpayne@68
|
1529 This is the classic Jim Blinn approach and will work in academic
|
|
jpayne@68
|
1530 environments where everything is done by the book. It has the shortcoming
|
|
jpayne@68
|
1531 of assuming that input PNG data with no gamma information is linear - this
|
|
jpayne@68
|
1532 is unlikely to be correct unless the PNG files were generated locally.
|
|
jpayne@68
|
1533 Most of the time the output precision will be so low as to show
|
|
jpayne@68
|
1534 significant banding in dark areas of the image.
|
|
jpayne@68
|
1535
|
|
jpayne@68
|
1536 png_set_expand_16(pp);
|
|
jpayne@68
|
1537 png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_DEFAULT_sRGB);
|
|
jpayne@68
|
1538
|
|
jpayne@68
|
1539 This is a somewhat more realistic Jim Blinn inspired approach. PNG files
|
|
jpayne@68
|
1540 are assumed to have the sRGB encoding if not marked with a gamma value and
|
|
jpayne@68
|
1541 the output is always 16 bits per component. This permits accurate scaling
|
|
jpayne@68
|
1542 and processing of the data. If you know that your input PNG files were
|
|
jpayne@68
|
1543 generated locally you might need to replace PNG_DEFAULT_sRGB with the
|
|
jpayne@68
|
1544 correct value for your system.
|
|
jpayne@68
|
1545
|
|
jpayne@68
|
1546 png_set_alpha_mode(pp, PNG_ALPHA_OPTIMIZED, PNG_DEFAULT_sRGB);
|
|
jpayne@68
|
1547
|
|
jpayne@68
|
1548 If you just need to composite the PNG image onto an existing background
|
|
jpayne@68
|
1549 and if you control the code that does this you can use the optimization
|
|
jpayne@68
|
1550 setting. In this case you just copy completely opaque pixels to the
|
|
jpayne@68
|
1551 output. For pixels that are not completely transparent (you just skip
|
|
jpayne@68
|
1552 those) you do the composition math using png_composite or png_composite_16
|
|
jpayne@68
|
1553 below then encode the resultant 8-bit or 16-bit values to match the output
|
|
jpayne@68
|
1554 encoding.
|
|
jpayne@68
|
1555
|
|
jpayne@68
|
1556 Other cases
|
|
jpayne@68
|
1557
|
|
jpayne@68
|
1558 If neither the PNG nor the standard linear encoding work for you because
|
|
jpayne@68
|
1559 of the software or hardware you use then you have a big problem. The PNG
|
|
jpayne@68
|
1560 case will probably result in halos around the image. The linear encoding
|
|
jpayne@68
|
1561 will probably result in a washed out, too bright, image (it's actually too
|
|
jpayne@68
|
1562 contrasty.) Try the ALPHA_OPTIMIZED mode above - this will probably
|
|
jpayne@68
|
1563 substantially reduce the halos. Alternatively try:
|
|
jpayne@68
|
1564
|
|
jpayne@68
|
1565 png_set_alpha_mode(pp, PNG_ALPHA_BROKEN, PNG_DEFAULT_sRGB);
|
|
jpayne@68
|
1566
|
|
jpayne@68
|
1567 This option will also reduce the halos, but there will be slight dark
|
|
jpayne@68
|
1568 halos round the opaque parts of the image where the background is light.
|
|
jpayne@68
|
1569 In the OPTIMIZED mode the halos will be light halos where the background
|
|
jpayne@68
|
1570 is dark. Take your pick - the halos are unavoidable unless you can get
|
|
jpayne@68
|
1571 your hardware/software fixed! (The OPTIMIZED approach is slightly
|
|
jpayne@68
|
1572 faster.)
|
|
jpayne@68
|
1573
|
|
jpayne@68
|
1574 When the default gamma of PNG files doesn't match the output gamma.
|
|
jpayne@68
|
1575 If you have PNG files with no gamma information png_set_alpha_mode allows
|
|
jpayne@68
|
1576 you to provide a default gamma, but it also sets the output gamma to the
|
|
jpayne@68
|
1577 matching value. If you know your PNG files have a gamma that doesn't
|
|
jpayne@68
|
1578 match the output you can take advantage of the fact that
|
|
jpayne@68
|
1579 png_set_alpha_mode always sets the output gamma but only sets the PNG
|
|
jpayne@68
|
1580 default if it is not already set:
|
|
jpayne@68
|
1581
|
|
jpayne@68
|
1582 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
|
|
jpayne@68
|
1583 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC);
|
|
jpayne@68
|
1584
|
|
jpayne@68
|
1585 The first call sets both the default and the output gamma values, the
|
|
jpayne@68
|
1586 second call overrides the output gamma without changing the default. This
|
|
jpayne@68
|
1587 is easier than achieving the same effect with png_set_gamma. You must use
|
|
jpayne@68
|
1588 PNG_ALPHA_PNG for the first call - internal checking in png_set_alpha will
|
|
jpayne@68
|
1589 fire if more than one call to png_set_alpha_mode and png_set_background is
|
|
jpayne@68
|
1590 made in the same read operation, however multiple calls with PNG_ALPHA_PNG
|
|
jpayne@68
|
1591 are ignored.
|
|
jpayne@68
|
1592
|
|
jpayne@68
|
1593 If you don't need, or can't handle, the alpha channel you can call
|
|
jpayne@68
|
1594 png_set_background() to remove it by compositing against a fixed color. Don't
|
|
jpayne@68
|
1595 call png_set_strip_alpha() to do this - it will leave spurious pixel values in
|
|
jpayne@68
|
1596 transparent parts of this image.
|
|
jpayne@68
|
1597
|
|
jpayne@68
|
1598 png_set_background(png_ptr, &background_color,
|
|
jpayne@68
|
1599 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1);
|
|
jpayne@68
|
1600
|
|
jpayne@68
|
1601 The background_color is an RGB or grayscale value according to the data format
|
|
jpayne@68
|
1602 libpng will produce for you. Because you don't yet know the format of the PNG
|
|
jpayne@68
|
1603 file, if you call png_set_background at this point you must arrange for the
|
|
jpayne@68
|
1604 format produced by libpng to always have 8-bit or 16-bit components and then
|
|
jpayne@68
|
1605 store the color as an 8-bit or 16-bit color as appropriate. The color contains
|
|
jpayne@68
|
1606 separate gray and RGB component values, so you can let libpng produce gray or
|
|
jpayne@68
|
1607 RGB output according to the input format, but low bit depth grayscale images
|
|
jpayne@68
|
1608 must always be converted to at least 8-bit format. (Even though low bit depth
|
|
jpayne@68
|
1609 grayscale images can't have an alpha channel they can have a transparent
|
|
jpayne@68
|
1610 color!)
|
|
jpayne@68
|
1611
|
|
jpayne@68
|
1612 You set the transforms you need later, either as flags to the high level
|
|
jpayne@68
|
1613 interface or libpng API calls for the low level interface. For reference the
|
|
jpayne@68
|
1614 settings and API calls required are:
|
|
jpayne@68
|
1615
|
|
jpayne@68
|
1616 8-bit values:
|
|
jpayne@68
|
1617 PNG_TRANSFORM_SCALE_16 | PNG_EXPAND
|
|
jpayne@68
|
1618 png_set_expand(png_ptr); png_set_scale_16(png_ptr);
|
|
jpayne@68
|
1619
|
|
jpayne@68
|
1620 If you must get exactly the same inaccurate results
|
|
jpayne@68
|
1621 produced by default in versions prior to libpng-1.5.4,
|
|
jpayne@68
|
1622 use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr)
|
|
jpayne@68
|
1623 instead.
|
|
jpayne@68
|
1624
|
|
jpayne@68
|
1625 16-bit values:
|
|
jpayne@68
|
1626 PNG_TRANSFORM_EXPAND_16
|
|
jpayne@68
|
1627 png_set_expand_16(png_ptr);
|
|
jpayne@68
|
1628
|
|
jpayne@68
|
1629 In either case palette image data will be expanded to RGB. If you just want
|
|
jpayne@68
|
1630 color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr)
|
|
jpayne@68
|
1631 to the list.
|
|
jpayne@68
|
1632
|
|
jpayne@68
|
1633 Calling png_set_background before the PNG file header is read will not work
|
|
jpayne@68
|
1634 prior to libpng-1.5.4. Because the failure may result in unexpected warnings or
|
|
jpayne@68
|
1635 errors it is therefore much safer to call png_set_background after the head has
|
|
jpayne@68
|
1636 been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be
|
|
jpayne@68
|
1637 used with the high level interface.
|
|
jpayne@68
|
1638
|
|
jpayne@68
|
1639 .SS The high-level read interface
|
|
jpayne@68
|
1640
|
|
jpayne@68
|
1641 At this point there are two ways to proceed; through the high-level
|
|
jpayne@68
|
1642 read interface, or through a sequence of low-level read operations.
|
|
jpayne@68
|
1643 You can use the high-level interface if (a) you are willing to read
|
|
jpayne@68
|
1644 the entire image into memory, and (b) the input transformations
|
|
jpayne@68
|
1645 you want to do are limited to the following set:
|
|
jpayne@68
|
1646
|
|
jpayne@68
|
1647 PNG_TRANSFORM_IDENTITY No transformation
|
|
jpayne@68
|
1648 PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to
|
|
jpayne@68
|
1649 8-bit accurately
|
|
jpayne@68
|
1650 PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to
|
|
jpayne@68
|
1651 8-bit less accurately
|
|
jpayne@68
|
1652 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
|
|
jpayne@68
|
1653 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
|
|
jpayne@68
|
1654 samples to bytes
|
|
jpayne@68
|
1655 PNG_TRANSFORM_PACKSWAP Change order of packed
|
|
jpayne@68
|
1656 pixels to LSB first
|
|
jpayne@68
|
1657 PNG_TRANSFORM_EXPAND Perform set_expand()
|
|
jpayne@68
|
1658 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
|
|
jpayne@68
|
1659 PNG_TRANSFORM_SHIFT Normalize pixels to the
|
|
jpayne@68
|
1660 sBIT depth
|
|
jpayne@68
|
1661 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
|
|
jpayne@68
|
1662 to BGRA
|
|
jpayne@68
|
1663 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
|
|
jpayne@68
|
1664 to AG
|
|
jpayne@68
|
1665 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
|
|
jpayne@68
|
1666 to transparency
|
|
jpayne@68
|
1667 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
|
|
jpayne@68
|
1668 PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
|
|
jpayne@68
|
1669 to RGB (or GA to RGBA)
|
|
jpayne@68
|
1670 PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits
|
|
jpayne@68
|
1671
|
|
jpayne@68
|
1672 (This excludes setting a background color, doing gamma transformation,
|
|
jpayne@68
|
1673 quantizing, and setting filler.) If this is the case, simply do this:
|
|
jpayne@68
|
1674
|
|
jpayne@68
|
1675 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
|
|
jpayne@68
|
1676
|
|
jpayne@68
|
1677 where png_transforms is an integer containing the bitwise OR of some
|
|
jpayne@68
|
1678 set of transformation flags. This call is equivalent to png_read_info(),
|
|
jpayne@68
|
1679 followed the set of transformations indicated by the transform mask,
|
|
jpayne@68
|
1680 then png_read_image(), and finally png_read_end().
|
|
jpayne@68
|
1681
|
|
jpayne@68
|
1682 (The final parameter of this call is not yet used. Someday it might point
|
|
jpayne@68
|
1683 to transformation parameters required by some future input transform.)
|
|
jpayne@68
|
1684
|
|
jpayne@68
|
1685 You must use png_transforms and not call any png_set_transform() functions
|
|
jpayne@68
|
1686 when you use png_read_png().
|
|
jpayne@68
|
1687
|
|
jpayne@68
|
1688 After you have called png_read_png(), you can retrieve the image data
|
|
jpayne@68
|
1689 with
|
|
jpayne@68
|
1690
|
|
jpayne@68
|
1691 row_pointers = png_get_rows(png_ptr, info_ptr);
|
|
jpayne@68
|
1692
|
|
jpayne@68
|
1693 where row_pointers is an array of pointers to the pixel data for each row:
|
|
jpayne@68
|
1694
|
|
jpayne@68
|
1695 png_bytep row_pointers[height];
|
|
jpayne@68
|
1696
|
|
jpayne@68
|
1697 If you know your image size and pixel size ahead of time, you can allocate
|
|
jpayne@68
|
1698 row_pointers prior to calling png_read_png() with
|
|
jpayne@68
|
1699
|
|
jpayne@68
|
1700 if (height > PNG_UINT_32_MAX / (sizeof (png_bytep)))
|
|
jpayne@68
|
1701 png_error(png_ptr,
|
|
jpayne@68
|
1702 "Image is too tall to process in memory");
|
|
jpayne@68
|
1703
|
|
jpayne@68
|
1704 if (width > PNG_UINT_32_MAX / pixel_size)
|
|
jpayne@68
|
1705 png_error(png_ptr,
|
|
jpayne@68
|
1706 "Image is too wide to process in memory");
|
|
jpayne@68
|
1707
|
|
jpayne@68
|
1708 row_pointers = png_malloc(png_ptr,
|
|
jpayne@68
|
1709 height*(sizeof (png_bytep)));
|
|
jpayne@68
|
1710
|
|
jpayne@68
|
1711 for (int i = 0; i < height, i++)
|
|
jpayne@68
|
1712 row_pointers[i] = NULL; /* security precaution */
|
|
jpayne@68
|
1713
|
|
jpayne@68
|
1714 for (int i = 0; i < height, i++)
|
|
jpayne@68
|
1715 row_pointers[i] = png_malloc(png_ptr,
|
|
jpayne@68
|
1716 width*pixel_size);
|
|
jpayne@68
|
1717
|
|
jpayne@68
|
1718 png_set_rows(png_ptr, info_ptr, &row_pointers);
|
|
jpayne@68
|
1719
|
|
jpayne@68
|
1720 Alternatively you could allocate your image in one big block and define
|
|
jpayne@68
|
1721 row_pointers[i] to point into the proper places in your block, but first
|
|
jpayne@68
|
1722 be sure that your platform is able to allocate such a large buffer:
|
|
jpayne@68
|
1723
|
|
jpayne@68
|
1724 /* Guard against integer overflow */
|
|
jpayne@68
|
1725 if (height > PNG_SIZE_MAX/(width*pixel_size))
|
|
jpayne@68
|
1726 png_error(png_ptr, "image_data buffer would be too large");
|
|
jpayne@68
|
1727
|
|
jpayne@68
|
1728 png_bytep buffer = png_malloc(png_ptr,
|
|
jpayne@68
|
1729 height*width*pixel_size);
|
|
jpayne@68
|
1730
|
|
jpayne@68
|
1731 for (int i = 0; i < height, i++)
|
|
jpayne@68
|
1732 row_pointers[i] = buffer + i*width*pixel_size;
|
|
jpayne@68
|
1733
|
|
jpayne@68
|
1734 png_set_rows(png_ptr, info_ptr, &row_pointers);
|
|
jpayne@68
|
1735
|
|
jpayne@68
|
1736 If you use png_set_rows(), the application is responsible for freeing
|
|
jpayne@68
|
1737 row_pointers (and row_pointers[i], if they were separately allocated).
|
|
jpayne@68
|
1738
|
|
jpayne@68
|
1739 If you don't allocate row_pointers ahead of time, png_read_png() will
|
|
jpayne@68
|
1740 do it, and it'll be free'ed by libpng when you call png_destroy_*().
|
|
jpayne@68
|
1741
|
|
jpayne@68
|
1742 .SS The low-level read interface
|
|
jpayne@68
|
1743
|
|
jpayne@68
|
1744 If you are going the low-level route, you are now ready to read all
|
|
jpayne@68
|
1745 the file information up to the actual image data. You do this with a
|
|
jpayne@68
|
1746 call to png_read_info().
|
|
jpayne@68
|
1747
|
|
jpayne@68
|
1748 png_read_info(png_ptr, info_ptr);
|
|
jpayne@68
|
1749
|
|
jpayne@68
|
1750 This will process all chunks up to but not including the image data.
|
|
jpayne@68
|
1751
|
|
jpayne@68
|
1752 This also copies some of the data from the PNG file into the decode structure
|
|
jpayne@68
|
1753 for use in later transformations. Important information copied in is:
|
|
jpayne@68
|
1754
|
|
jpayne@68
|
1755 1) The PNG file gamma from the gAMA chunk. This overwrites the default value
|
|
jpayne@68
|
1756 provided by an earlier call to png_set_gamma or png_set_alpha_mode.
|
|
jpayne@68
|
1757
|
|
jpayne@68
|
1758 2) Prior to libpng-1.5.4 the background color from a bKGd chunk. This
|
|
jpayne@68
|
1759 damages the information provided by an earlier call to png_set_background
|
|
jpayne@68
|
1760 resulting in unexpected behavior. Libpng-1.5.4 no longer does this.
|
|
jpayne@68
|
1761
|
|
jpayne@68
|
1762 3) The number of significant bits in each component value. Libpng uses this to
|
|
jpayne@68
|
1763 optimize gamma handling by reducing the internal lookup table sizes.
|
|
jpayne@68
|
1764
|
|
jpayne@68
|
1765 4) The transparent color information from a tRNS chunk. This can be modified by
|
|
jpayne@68
|
1766 a later call to png_set_tRNS.
|
|
jpayne@68
|
1767
|
|
jpayne@68
|
1768 .SS Querying the info structure
|
|
jpayne@68
|
1769
|
|
jpayne@68
|
1770 Functions are used to get the information from the info_ptr once it
|
|
jpayne@68
|
1771 has been read. Note that these fields may not be completely filled
|
|
jpayne@68
|
1772 in until png_read_end() has read the chunk data following the image.
|
|
jpayne@68
|
1773
|
|
jpayne@68
|
1774 png_get_IHDR(png_ptr, info_ptr, &width, &height,
|
|
jpayne@68
|
1775 &bit_depth, &color_type, &interlace_type,
|
|
jpayne@68
|
1776 &compression_type, &filter_method);
|
|
jpayne@68
|
1777
|
|
jpayne@68
|
1778 width - holds the width of the image
|
|
jpayne@68
|
1779 in pixels (up to 2^31).
|
|
jpayne@68
|
1780
|
|
jpayne@68
|
1781 height - holds the height of the image
|
|
jpayne@68
|
1782 in pixels (up to 2^31).
|
|
jpayne@68
|
1783
|
|
jpayne@68
|
1784 bit_depth - holds the bit depth of one of the
|
|
jpayne@68
|
1785 image channels. (valid values are
|
|
jpayne@68
|
1786 1, 2, 4, 8, 16 and depend also on
|
|
jpayne@68
|
1787 the color_type. See also
|
|
jpayne@68
|
1788 significant bits (sBIT) below).
|
|
jpayne@68
|
1789
|
|
jpayne@68
|
1790 color_type - describes which color/alpha channels
|
|
jpayne@68
|
1791 are present.
|
|
jpayne@68
|
1792 PNG_COLOR_TYPE_GRAY
|
|
jpayne@68
|
1793 (bit depths 1, 2, 4, 8, 16)
|
|
jpayne@68
|
1794 PNG_COLOR_TYPE_GRAY_ALPHA
|
|
jpayne@68
|
1795 (bit depths 8, 16)
|
|
jpayne@68
|
1796 PNG_COLOR_TYPE_PALETTE
|
|
jpayne@68
|
1797 (bit depths 1, 2, 4, 8)
|
|
jpayne@68
|
1798 PNG_COLOR_TYPE_RGB
|
|
jpayne@68
|
1799 (bit_depths 8, 16)
|
|
jpayne@68
|
1800 PNG_COLOR_TYPE_RGB_ALPHA
|
|
jpayne@68
|
1801 (bit_depths 8, 16)
|
|
jpayne@68
|
1802
|
|
jpayne@68
|
1803 PNG_COLOR_MASK_PALETTE
|
|
jpayne@68
|
1804 PNG_COLOR_MASK_COLOR
|
|
jpayne@68
|
1805 PNG_COLOR_MASK_ALPHA
|
|
jpayne@68
|
1806
|
|
jpayne@68
|
1807 interlace_type - (PNG_INTERLACE_NONE or
|
|
jpayne@68
|
1808 PNG_INTERLACE_ADAM7)
|
|
jpayne@68
|
1809
|
|
jpayne@68
|
1810 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
|
|
jpayne@68
|
1811 for PNG 1.0)
|
|
jpayne@68
|
1812
|
|
jpayne@68
|
1813 filter_method - (must be PNG_FILTER_TYPE_BASE
|
|
jpayne@68
|
1814 for PNG 1.0, and can also be
|
|
jpayne@68
|
1815 PNG_INTRAPIXEL_DIFFERENCING if
|
|
jpayne@68
|
1816 the PNG datastream is embedded in
|
|
jpayne@68
|
1817 a MNG-1.0 datastream)
|
|
jpayne@68
|
1818
|
|
jpayne@68
|
1819 Any of width, height, color_type, bit_depth,
|
|
jpayne@68
|
1820 interlace_type, compression_type, or filter_method can
|
|
jpayne@68
|
1821 be NULL if you are not interested in their values.
|
|
jpayne@68
|
1822
|
|
jpayne@68
|
1823 Note that png_get_IHDR() returns 32-bit data into
|
|
jpayne@68
|
1824 the application's width and height variables.
|
|
jpayne@68
|
1825 This is an unsafe situation if these are not png_uint_32
|
|
jpayne@68
|
1826 variables. In such situations, the
|
|
jpayne@68
|
1827 png_get_image_width() and png_get_image_height()
|
|
jpayne@68
|
1828 functions described below are safer.
|
|
jpayne@68
|
1829
|
|
jpayne@68
|
1830 width = png_get_image_width(png_ptr,
|
|
jpayne@68
|
1831 info_ptr);
|
|
jpayne@68
|
1832
|
|
jpayne@68
|
1833 height = png_get_image_height(png_ptr,
|
|
jpayne@68
|
1834 info_ptr);
|
|
jpayne@68
|
1835
|
|
jpayne@68
|
1836 bit_depth = png_get_bit_depth(png_ptr,
|
|
jpayne@68
|
1837 info_ptr);
|
|
jpayne@68
|
1838
|
|
jpayne@68
|
1839 color_type = png_get_color_type(png_ptr,
|
|
jpayne@68
|
1840 info_ptr);
|
|
jpayne@68
|
1841
|
|
jpayne@68
|
1842 interlace_type = png_get_interlace_type(png_ptr,
|
|
jpayne@68
|
1843 info_ptr);
|
|
jpayne@68
|
1844
|
|
jpayne@68
|
1845 compression_type = png_get_compression_type(png_ptr,
|
|
jpayne@68
|
1846 info_ptr);
|
|
jpayne@68
|
1847
|
|
jpayne@68
|
1848 filter_method = png_get_filter_type(png_ptr,
|
|
jpayne@68
|
1849 info_ptr);
|
|
jpayne@68
|
1850
|
|
jpayne@68
|
1851 channels = png_get_channels(png_ptr, info_ptr);
|
|
jpayne@68
|
1852
|
|
jpayne@68
|
1853 channels - number of channels of info for the
|
|
jpayne@68
|
1854 color type (valid values are 1 (GRAY,
|
|
jpayne@68
|
1855 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
|
|
jpayne@68
|
1856 4 (RGB_ALPHA or RGB + filler byte))
|
|
jpayne@68
|
1857
|
|
jpayne@68
|
1858 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
|
|
jpayne@68
|
1859
|
|
jpayne@68
|
1860 rowbytes - number of bytes needed to hold a row
|
|
jpayne@68
|
1861 This value, the bit_depth, color_type,
|
|
jpayne@68
|
1862 and the number of channels can change
|
|
jpayne@68
|
1863 if you use transforms such as
|
|
jpayne@68
|
1864 png_set_expand(). See
|
|
jpayne@68
|
1865 png_read_update_info(), below.
|
|
jpayne@68
|
1866
|
|
jpayne@68
|
1867 signature = png_get_signature(png_ptr, info_ptr);
|
|
jpayne@68
|
1868
|
|
jpayne@68
|
1869 signature - holds the signature read from the
|
|
jpayne@68
|
1870 file (if any). The data is kept in
|
|
jpayne@68
|
1871 the same offset it would be if the
|
|
jpayne@68
|
1872 whole signature were read (i.e. if an
|
|
jpayne@68
|
1873 application had already read in 4
|
|
jpayne@68
|
1874 bytes of signature before starting
|
|
jpayne@68
|
1875 libpng, the remaining 4 bytes would
|
|
jpayne@68
|
1876 be in signature[4] through signature[7]
|
|
jpayne@68
|
1877 (see png_set_sig_bytes())).
|
|
jpayne@68
|
1878
|
|
jpayne@68
|
1879 These are also important, but their validity depends on whether the chunk
|
|
jpayne@68
|
1880 has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
|
|
jpayne@68
|
1881 png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
|
|
jpayne@68
|
1882 data has been read, or zero if it is missing. The parameters to the
|
|
jpayne@68
|
1883 png_get_<chunk> are set directly if they are simple data types, or a
|
|
jpayne@68
|
1884 pointer into the info_ptr is returned for any complex types.
|
|
jpayne@68
|
1885
|
|
jpayne@68
|
1886 The colorspace data from gAMA, cHRM, sRGB, iCCP, and sBIT chunks
|
|
jpayne@68
|
1887 is simply returned to give the application information about how the
|
|
jpayne@68
|
1888 image was encoded. Libpng itself only does transformations using the file
|
|
jpayne@68
|
1889 gamma when combining semitransparent pixels with the background color, and,
|
|
jpayne@68
|
1890 since libpng-1.6.0, when converting between 8-bit sRGB and 16-bit linear pixels
|
|
jpayne@68
|
1891 within the simplified API. Libpng also uses the file gamma when converting
|
|
jpayne@68
|
1892 RGB to gray, beginning with libpng-1.0.5, if the application calls
|
|
jpayne@68
|
1893 png_set_rgb_to_gray()).
|
|
jpayne@68
|
1894
|
|
jpayne@68
|
1895 png_get_PLTE(png_ptr, info_ptr, &palette,
|
|
jpayne@68
|
1896 &num_palette);
|
|
jpayne@68
|
1897
|
|
jpayne@68
|
1898 palette - the palette for the file
|
|
jpayne@68
|
1899 (array of png_color)
|
|
jpayne@68
|
1900
|
|
jpayne@68
|
1901 num_palette - number of entries in the palette
|
|
jpayne@68
|
1902
|
|
jpayne@68
|
1903 png_get_gAMA(png_ptr, info_ptr, &file_gamma);
|
|
jpayne@68
|
1904 png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma);
|
|
jpayne@68
|
1905
|
|
jpayne@68
|
1906 file_gamma - the gamma at which the file is
|
|
jpayne@68
|
1907 written (PNG_INFO_gAMA)
|
|
jpayne@68
|
1908
|
|
jpayne@68
|
1909 int_file_gamma - 100,000 times the gamma at which the
|
|
jpayne@68
|
1910 file is written
|
|
jpayne@68
|
1911
|
|
jpayne@68
|
1912 png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x,
|
|
jpayne@68
|
1913 &red_y, &green_x, &green_y, &blue_x, &blue_y)
|
|
jpayne@68
|
1914 png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z,
|
|
jpayne@68
|
1915 &green_X, &green_Y, &green_Z, &blue_X, &blue_Y,
|
|
jpayne@68
|
1916 &blue_Z)
|
|
jpayne@68
|
1917 png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x,
|
|
jpayne@68
|
1918 &int_white_y, &int_red_x, &int_red_y,
|
|
jpayne@68
|
1919 &int_green_x, &int_green_y, &int_blue_x,
|
|
jpayne@68
|
1920 &int_blue_y)
|
|
jpayne@68
|
1921 png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y,
|
|
jpayne@68
|
1922 &int_red_Z, &int_green_X, &int_green_Y,
|
|
jpayne@68
|
1923 &int_green_Z, &int_blue_X, &int_blue_Y,
|
|
jpayne@68
|
1924 &int_blue_Z)
|
|
jpayne@68
|
1925
|
|
jpayne@68
|
1926 {white,red,green,blue}_{x,y}
|
|
jpayne@68
|
1927 A color space encoding specified using the
|
|
jpayne@68
|
1928 chromaticities of the end points and the
|
|
jpayne@68
|
1929 white point. (PNG_INFO_cHRM)
|
|
jpayne@68
|
1930
|
|
jpayne@68
|
1931 {red,green,blue}_{X,Y,Z}
|
|
jpayne@68
|
1932 A color space encoding specified using the
|
|
jpayne@68
|
1933 encoding end points - the CIE tristimulus
|
|
jpayne@68
|
1934 specification of the intended color of the red,
|
|
jpayne@68
|
1935 green and blue channels in the PNG RGB data.
|
|
jpayne@68
|
1936 The white point is simply the sum of the three
|
|
jpayne@68
|
1937 end points. (PNG_INFO_cHRM)
|
|
jpayne@68
|
1938
|
|
jpayne@68
|
1939 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
|
|
jpayne@68
|
1940
|
|
jpayne@68
|
1941 srgb_intent - the rendering intent (PNG_INFO_sRGB)
|
|
jpayne@68
|
1942 The presence of the sRGB chunk
|
|
jpayne@68
|
1943 means that the pixel data is in the
|
|
jpayne@68
|
1944 sRGB color space. This chunk also
|
|
jpayne@68
|
1945 implies specific values of gAMA and
|
|
jpayne@68
|
1946 cHRM.
|
|
jpayne@68
|
1947
|
|
jpayne@68
|
1948 png_get_iCCP(png_ptr, info_ptr, &name,
|
|
jpayne@68
|
1949 &compression_type, &profile, &proflen);
|
|
jpayne@68
|
1950
|
|
jpayne@68
|
1951 name - The profile name.
|
|
jpayne@68
|
1952
|
|
jpayne@68
|
1953 compression_type - The compression type; always
|
|
jpayne@68
|
1954 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
|
|
jpayne@68
|
1955 You may give NULL to this argument to
|
|
jpayne@68
|
1956 ignore it.
|
|
jpayne@68
|
1957
|
|
jpayne@68
|
1958 profile - International Color Consortium color
|
|
jpayne@68
|
1959 profile data. May contain NULs.
|
|
jpayne@68
|
1960
|
|
jpayne@68
|
1961 proflen - length of profile data in bytes.
|
|
jpayne@68
|
1962
|
|
jpayne@68
|
1963 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
|
|
jpayne@68
|
1964
|
|
jpayne@68
|
1965 sig_bit - the number of significant bits for
|
|
jpayne@68
|
1966 (PNG_INFO_sBIT) each of the gray,
|
|
jpayne@68
|
1967 red, green, and blue channels,
|
|
jpayne@68
|
1968 whichever are appropriate for the
|
|
jpayne@68
|
1969 given color type (png_color_16)
|
|
jpayne@68
|
1970
|
|
jpayne@68
|
1971 png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
|
|
jpayne@68
|
1972 &num_trans, &trans_color);
|
|
jpayne@68
|
1973
|
|
jpayne@68
|
1974 trans_alpha - array of alpha (transparency)
|
|
jpayne@68
|
1975 entries for palette (PNG_INFO_tRNS)
|
|
jpayne@68
|
1976
|
|
jpayne@68
|
1977 num_trans - number of transparent entries
|
|
jpayne@68
|
1978 (PNG_INFO_tRNS)
|
|
jpayne@68
|
1979
|
|
jpayne@68
|
1980 trans_color - graylevel or color sample values of
|
|
jpayne@68
|
1981 the single transparent color for
|
|
jpayne@68
|
1982 non-paletted images (PNG_INFO_tRNS)
|
|
jpayne@68
|
1983
|
|
jpayne@68
|
1984 png_get_eXIf_1(png_ptr, info_ptr, &num_exif, &exif);
|
|
jpayne@68
|
1985
|
|
jpayne@68
|
1986 exif - Exif profile (array of png_byte)
|
|
jpayne@68
|
1987 (PNG_INFO_eXIf)
|
|
jpayne@68
|
1988
|
|
jpayne@68
|
1989 png_get_hIST(png_ptr, info_ptr, &hist);
|
|
jpayne@68
|
1990
|
|
jpayne@68
|
1991 hist - histogram of palette (array of
|
|
jpayne@68
|
1992 png_uint_16) (PNG_INFO_hIST)
|
|
jpayne@68
|
1993
|
|
jpayne@68
|
1994 png_get_tIME(png_ptr, info_ptr, &mod_time);
|
|
jpayne@68
|
1995
|
|
jpayne@68
|
1996 mod_time - time image was last modified
|
|
jpayne@68
|
1997 (PNG_INFO_tIME)
|
|
jpayne@68
|
1998
|
|
jpayne@68
|
1999 png_get_bKGD(png_ptr, info_ptr, &background);
|
|
jpayne@68
|
2000
|
|
jpayne@68
|
2001 background - background color (of type
|
|
jpayne@68
|
2002 png_color_16p) (PNG_INFO_bKGD)
|
|
jpayne@68
|
2003 valid 16-bit red, green and blue
|
|
jpayne@68
|
2004 values, regardless of color_type
|
|
jpayne@68
|
2005
|
|
jpayne@68
|
2006 num_comments = png_get_text(png_ptr, info_ptr,
|
|
jpayne@68
|
2007 &text_ptr, &num_text);
|
|
jpayne@68
|
2008
|
|
jpayne@68
|
2009 num_comments - number of comments
|
|
jpayne@68
|
2010
|
|
jpayne@68
|
2011 text_ptr - array of png_text holding image
|
|
jpayne@68
|
2012 comments
|
|
jpayne@68
|
2013
|
|
jpayne@68
|
2014 text_ptr[i].compression - type of compression used
|
|
jpayne@68
|
2015 on "text" PNG_TEXT_COMPRESSION_NONE
|
|
jpayne@68
|
2016 PNG_TEXT_COMPRESSION_zTXt
|
|
jpayne@68
|
2017 PNG_ITXT_COMPRESSION_NONE
|
|
jpayne@68
|
2018 PNG_ITXT_COMPRESSION_zTXt
|
|
jpayne@68
|
2019
|
|
jpayne@68
|
2020 text_ptr[i].key - keyword for comment. Must contain
|
|
jpayne@68
|
2021 1-79 characters.
|
|
jpayne@68
|
2022
|
|
jpayne@68
|
2023 text_ptr[i].text - text comments for current
|
|
jpayne@68
|
2024 keyword. Can be empty.
|
|
jpayne@68
|
2025
|
|
jpayne@68
|
2026 text_ptr[i].text_length - length of text string,
|
|
jpayne@68
|
2027 after decompression, 0 for iTXt
|
|
jpayne@68
|
2028
|
|
jpayne@68
|
2029 text_ptr[i].itxt_length - length of itxt string,
|
|
jpayne@68
|
2030 after decompression, 0 for tEXt/zTXt
|
|
jpayne@68
|
2031
|
|
jpayne@68
|
2032 text_ptr[i].lang - language of comment (empty
|
|
jpayne@68
|
2033 string for unknown).
|
|
jpayne@68
|
2034
|
|
jpayne@68
|
2035 text_ptr[i].lang_key - keyword in UTF-8
|
|
jpayne@68
|
2036 (empty string for unknown).
|
|
jpayne@68
|
2037
|
|
jpayne@68
|
2038 Note that the itxt_length, lang, and lang_key
|
|
jpayne@68
|
2039 members of the text_ptr structure only exist when the
|
|
jpayne@68
|
2040 library is built with iTXt chunk support. Prior to
|
|
jpayne@68
|
2041 libpng-1.4.0 the library was built by default without
|
|
jpayne@68
|
2042 iTXt support. Also note that when iTXt is supported,
|
|
jpayne@68
|
2043 they contain NULL pointers when the "compression"
|
|
jpayne@68
|
2044 field contains PNG_TEXT_COMPRESSION_NONE or
|
|
jpayne@68
|
2045 PNG_TEXT_COMPRESSION_zTXt.
|
|
jpayne@68
|
2046
|
|
jpayne@68
|
2047 num_text - number of comments (same as
|
|
jpayne@68
|
2048 num_comments; you can put NULL here
|
|
jpayne@68
|
2049 to avoid the duplication)
|
|
jpayne@68
|
2050
|
|
jpayne@68
|
2051 Note while png_set_text() will accept text, language,
|
|
jpayne@68
|
2052 and translated keywords that can be NULL pointers, the
|
|
jpayne@68
|
2053 structure returned by png_get_text will always contain
|
|
jpayne@68
|
2054 regular zero-terminated C strings. They might be
|
|
jpayne@68
|
2055 empty strings but they will never be NULL pointers.
|
|
jpayne@68
|
2056
|
|
jpayne@68
|
2057 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
|
|
jpayne@68
|
2058 &palette_ptr);
|
|
jpayne@68
|
2059
|
|
jpayne@68
|
2060 num_spalettes - number of sPLT chunks read.
|
|
jpayne@68
|
2061
|
|
jpayne@68
|
2062 palette_ptr - array of palette structures holding
|
|
jpayne@68
|
2063 contents of one or more sPLT chunks
|
|
jpayne@68
|
2064 read.
|
|
jpayne@68
|
2065
|
|
jpayne@68
|
2066 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
|
|
jpayne@68
|
2067 &unit_type);
|
|
jpayne@68
|
2068
|
|
jpayne@68
|
2069 offset_x - positive offset from the left edge
|
|
jpayne@68
|
2070 of the screen (can be negative)
|
|
jpayne@68
|
2071
|
|
jpayne@68
|
2072 offset_y - positive offset from the top edge
|
|
jpayne@68
|
2073 of the screen (can be negative)
|
|
jpayne@68
|
2074
|
|
jpayne@68
|
2075 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
|
|
jpayne@68
|
2076
|
|
jpayne@68
|
2077 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
|
|
jpayne@68
|
2078 &unit_type);
|
|
jpayne@68
|
2079
|
|
jpayne@68
|
2080 res_x - pixels/unit physical resolution in
|
|
jpayne@68
|
2081 x direction
|
|
jpayne@68
|
2082
|
|
jpayne@68
|
2083 res_y - pixels/unit physical resolution in
|
|
jpayne@68
|
2084 x direction
|
|
jpayne@68
|
2085
|
|
jpayne@68
|
2086 unit_type - PNG_RESOLUTION_UNKNOWN,
|
|
jpayne@68
|
2087 PNG_RESOLUTION_METER
|
|
jpayne@68
|
2088
|
|
jpayne@68
|
2089 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
|
|
jpayne@68
|
2090 &height)
|
|
jpayne@68
|
2091
|
|
jpayne@68
|
2092 unit - physical scale units (an integer)
|
|
jpayne@68
|
2093
|
|
jpayne@68
|
2094 width - width of a pixel in physical scale units
|
|
jpayne@68
|
2095
|
|
jpayne@68
|
2096 height - height of a pixel in physical scale units
|
|
jpayne@68
|
2097 (width and height are doubles)
|
|
jpayne@68
|
2098
|
|
jpayne@68
|
2099 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
|
|
jpayne@68
|
2100 &height)
|
|
jpayne@68
|
2101
|
|
jpayne@68
|
2102 unit - physical scale units (an integer)
|
|
jpayne@68
|
2103
|
|
jpayne@68
|
2104 width - width of a pixel in physical scale units
|
|
jpayne@68
|
2105 (expressed as a string)
|
|
jpayne@68
|
2106
|
|
jpayne@68
|
2107 height - height of a pixel in physical scale units
|
|
jpayne@68
|
2108 (width and height are strings like "2.54")
|
|
jpayne@68
|
2109
|
|
jpayne@68
|
2110 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
|
|
jpayne@68
|
2111 info_ptr, &unknowns)
|
|
jpayne@68
|
2112
|
|
jpayne@68
|
2113 unknowns - array of png_unknown_chunk
|
|
jpayne@68
|
2114 structures holding unknown chunks
|
|
jpayne@68
|
2115
|
|
jpayne@68
|
2116 unknowns[i].name - name of unknown chunk
|
|
jpayne@68
|
2117
|
|
jpayne@68
|
2118 unknowns[i].data - data of unknown chunk
|
|
jpayne@68
|
2119
|
|
jpayne@68
|
2120 unknowns[i].size - size of unknown chunk's data
|
|
jpayne@68
|
2121
|
|
jpayne@68
|
2122 unknowns[i].location - position of chunk in file
|
|
jpayne@68
|
2123
|
|
jpayne@68
|
2124 The value of "i" corresponds to the order in which the
|
|
jpayne@68
|
2125 chunks were read from the PNG file or inserted with the
|
|
jpayne@68
|
2126 png_set_unknown_chunks() function.
|
|
jpayne@68
|
2127
|
|
jpayne@68
|
2128 The value of "location" is a bitwise "or" of
|
|
jpayne@68
|
2129
|
|
jpayne@68
|
2130 PNG_HAVE_IHDR (0x01)
|
|
jpayne@68
|
2131 PNG_HAVE_PLTE (0x02)
|
|
jpayne@68
|
2132 PNG_AFTER_IDAT (0x08)
|
|
jpayne@68
|
2133
|
|
jpayne@68
|
2134 The data from the pHYs chunk can be retrieved in several convenient
|
|
jpayne@68
|
2135 forms:
|
|
jpayne@68
|
2136
|
|
jpayne@68
|
2137 res_x = png_get_x_pixels_per_meter(png_ptr,
|
|
jpayne@68
|
2138 info_ptr)
|
|
jpayne@68
|
2139
|
|
jpayne@68
|
2140 res_y = png_get_y_pixels_per_meter(png_ptr,
|
|
jpayne@68
|
2141 info_ptr)
|
|
jpayne@68
|
2142
|
|
jpayne@68
|
2143 res_x_and_y = png_get_pixels_per_meter(png_ptr,
|
|
jpayne@68
|
2144 info_ptr)
|
|
jpayne@68
|
2145
|
|
jpayne@68
|
2146 res_x = png_get_x_pixels_per_inch(png_ptr,
|
|
jpayne@68
|
2147 info_ptr)
|
|
jpayne@68
|
2148
|
|
jpayne@68
|
2149 res_y = png_get_y_pixels_per_inch(png_ptr,
|
|
jpayne@68
|
2150 info_ptr)
|
|
jpayne@68
|
2151
|
|
jpayne@68
|
2152 res_x_and_y = png_get_pixels_per_inch(png_ptr,
|
|
jpayne@68
|
2153 info_ptr)
|
|
jpayne@68
|
2154
|
|
jpayne@68
|
2155 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
|
|
jpayne@68
|
2156 info_ptr)
|
|
jpayne@68
|
2157
|
|
jpayne@68
|
2158 Each of these returns 0 [signifying "unknown"] if
|
|
jpayne@68
|
2159 the data is not present or if res_x is 0;
|
|
jpayne@68
|
2160 res_x_and_y is 0 if res_x != res_y
|
|
jpayne@68
|
2161
|
|
jpayne@68
|
2162 Note that because of the way the resolutions are
|
|
jpayne@68
|
2163 stored internally, the inch conversions won't
|
|
jpayne@68
|
2164 come out to exactly even number. For example,
|
|
jpayne@68
|
2165 72 dpi is stored as 0.28346 pixels/meter, and
|
|
jpayne@68
|
2166 when this is retrieved it is 71.9988 dpi, so
|
|
jpayne@68
|
2167 be sure to round the returned value appropriately
|
|
jpayne@68
|
2168 if you want to display a reasonable-looking result.
|
|
jpayne@68
|
2169
|
|
jpayne@68
|
2170 The data from the oFFs chunk can be retrieved in several convenient
|
|
jpayne@68
|
2171 forms:
|
|
jpayne@68
|
2172
|
|
jpayne@68
|
2173 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
|
|
jpayne@68
|
2174
|
|
jpayne@68
|
2175 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
|
|
jpayne@68
|
2176
|
|
jpayne@68
|
2177 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
|
|
jpayne@68
|
2178
|
|
jpayne@68
|
2179 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
|
|
jpayne@68
|
2180
|
|
jpayne@68
|
2181 Each of these returns 0 [signifying "unknown" if both
|
|
jpayne@68
|
2182 x and y are 0] if the data is not present or if the
|
|
jpayne@68
|
2183 chunk is present but the unit is the pixel. The
|
|
jpayne@68
|
2184 remark about inexact inch conversions applies here
|
|
jpayne@68
|
2185 as well, because a value in inches can't always be
|
|
jpayne@68
|
2186 converted to microns and back without some loss
|
|
jpayne@68
|
2187 of precision.
|
|
jpayne@68
|
2188
|
|
jpayne@68
|
2189 For more information, see the
|
|
jpayne@68
|
2190 PNG specification for chunk contents. Be careful with trusting
|
|
jpayne@68
|
2191 rowbytes, as some of the transformations could increase the space
|
|
jpayne@68
|
2192 needed to hold a row (expand, filler, gray_to_rgb, etc.).
|
|
jpayne@68
|
2193 See png_read_update_info(), below.
|
|
jpayne@68
|
2194
|
|
jpayne@68
|
2195 A quick word about text_ptr and num_text. PNG stores comments in
|
|
jpayne@68
|
2196 keyword/text pairs, one pair per chunk, with no limit on the number
|
|
jpayne@68
|
2197 of text chunks, and a 2^31 byte limit on their size. While there are
|
|
jpayne@68
|
2198 suggested keywords, there is no requirement to restrict the use to these
|
|
jpayne@68
|
2199 strings. It is strongly suggested that keywords and text be sensible
|
|
jpayne@68
|
2200 to humans (that's the point), so don't use abbreviations. Non-printing
|
|
jpayne@68
|
2201 symbols are not allowed. See the PNG specification for more details.
|
|
jpayne@68
|
2202 There is also no requirement to have text after the keyword.
|
|
jpayne@68
|
2203
|
|
jpayne@68
|
2204 Keywords should be limited to 79 Latin-1 characters without leading or
|
|
jpayne@68
|
2205 trailing spaces, but non-consecutive spaces are allowed within the
|
|
jpayne@68
|
2206 keyword. It is possible to have the same keyword any number of times.
|
|
jpayne@68
|
2207 The text_ptr is an array of png_text structures, each holding a
|
|
jpayne@68
|
2208 pointer to a language string, a pointer to a keyword and a pointer to
|
|
jpayne@68
|
2209 a text string. The text string, language code, and translated
|
|
jpayne@68
|
2210 keyword may be empty or NULL pointers. The keyword/text
|
|
jpayne@68
|
2211 pairs are put into the array in the order that they are received.
|
|
jpayne@68
|
2212 However, some or all of the text chunks may be after the image, so, to
|
|
jpayne@68
|
2213 make sure you have read all the text chunks, don't mess with these
|
|
jpayne@68
|
2214 until after you read the stuff after the image. This will be
|
|
jpayne@68
|
2215 mentioned again below in the discussion that goes with png_read_end().
|
|
jpayne@68
|
2216
|
|
jpayne@68
|
2217 .SS Input transformations
|
|
jpayne@68
|
2218
|
|
jpayne@68
|
2219 After you've read the header information, you can set up the library
|
|
jpayne@68
|
2220 to handle any special transformations of the image data. The various
|
|
jpayne@68
|
2221 ways to transform the data will be described in the order that they
|
|
jpayne@68
|
2222 should occur. This is important, as some of these change the color
|
|
jpayne@68
|
2223 type and/or bit depth of the data, and some others only work on
|
|
jpayne@68
|
2224 certain color types and bit depths.
|
|
jpayne@68
|
2225
|
|
jpayne@68
|
2226 Transformations you request are ignored if they don't have any meaning for a
|
|
jpayne@68
|
2227 particular input data format. However some transformations can have an effect
|
|
jpayne@68
|
2228 as a result of a previous transformation. If you specify a contradictory set of
|
|
jpayne@68
|
2229 transformations, for example both adding and removing the alpha channel, you
|
|
jpayne@68
|
2230 cannot predict the final result.
|
|
jpayne@68
|
2231
|
|
jpayne@68
|
2232 The color used for the transparency values should be supplied in the same
|
|
jpayne@68
|
2233 format/depth as the current image data. It is stored in the same format/depth
|
|
jpayne@68
|
2234 as the image data in a tRNS chunk, so this is what libpng expects for this data.
|
|
jpayne@68
|
2235
|
|
jpayne@68
|
2236 The color used for the background value depends on the need_expand argument as
|
|
jpayne@68
|
2237 described below.
|
|
jpayne@68
|
2238
|
|
jpayne@68
|
2239 Data will be decoded into the supplied row buffers packed into bytes
|
|
jpayne@68
|
2240 unless the library has been told to transform it into another format.
|
|
jpayne@68
|
2241 For example, 4 bit/pixel paletted or grayscale data will be returned
|
|
jpayne@68
|
2242 2 pixels/byte with the leftmost pixel in the high-order bits of the byte,
|
|
jpayne@68
|
2243 unless png_set_packing() is called. 8-bit RGB data will be stored
|
|
jpayne@68
|
2244 in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
|
|
jpayne@68
|
2245 is called to insert filler bytes, either before or after each RGB triplet.
|
|
jpayne@68
|
2246
|
|
jpayne@68
|
2247 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
|
|
jpayne@68
|
2248 byte of the color value first, unless png_set_scale_16() is called to
|
|
jpayne@68
|
2249 transform it to regular RGB RGB triplets, or png_set_filler() or
|
|
jpayne@68
|
2250 png_set_add alpha() is called to insert two filler bytes, either before
|
|
jpayne@68
|
2251 or after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
|
|
jpayne@68
|
2252 be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(),
|
|
jpayne@68
|
2253 or png_set_scale_16().
|
|
jpayne@68
|
2254
|
|
jpayne@68
|
2255 The following code transforms grayscale images of less than 8 to 8 bits,
|
|
jpayne@68
|
2256 changes paletted images to RGB, and adds a full alpha channel if there is
|
|
jpayne@68
|
2257 transparency information in a tRNS chunk. This is most useful on
|
|
jpayne@68
|
2258 grayscale images with bit depths of 2 or 4 or if there is a multiple-image
|
|
jpayne@68
|
2259 viewing application that wishes to treat all images in the same way.
|
|
jpayne@68
|
2260
|
|
jpayne@68
|
2261 if (color_type == PNG_COLOR_TYPE_PALETTE)
|
|
jpayne@68
|
2262 png_set_palette_to_rgb(png_ptr);
|
|
jpayne@68
|
2263
|
|
jpayne@68
|
2264 if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
|
|
jpayne@68
|
2265 png_set_tRNS_to_alpha(png_ptr);
|
|
jpayne@68
|
2266
|
|
jpayne@68
|
2267 if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
|
|
jpayne@68
|
2268 png_set_expand_gray_1_2_4_to_8(png_ptr);
|
|
jpayne@68
|
2269
|
|
jpayne@68
|
2270 The first two functions are actually aliases for png_set_expand(), added
|
|
jpayne@68
|
2271 in libpng version 1.0.4, with the function names expanded to improve code
|
|
jpayne@68
|
2272 readability. In some future version they may actually do different
|
|
jpayne@68
|
2273 things.
|
|
jpayne@68
|
2274
|
|
jpayne@68
|
2275 As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
|
|
jpayne@68
|
2276 added. It expands the sample depth without changing tRNS to alpha.
|
|
jpayne@68
|
2277
|
|
jpayne@68
|
2278 As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as
|
|
jpayne@68
|
2279 png_set_expand(); however, the resultant channels have 16 bits rather than 8.
|
|
jpayne@68
|
2280 Use this when the output color or gray channels are made linear to avoid fairly
|
|
jpayne@68
|
2281 severe accuracy loss.
|
|
jpayne@68
|
2282
|
|
jpayne@68
|
2283 if (bit_depth < 16)
|
|
jpayne@68
|
2284 png_set_expand_16(png_ptr);
|
|
jpayne@68
|
2285
|
|
jpayne@68
|
2286 PNG can have files with 16 bits per channel. If you only can handle
|
|
jpayne@68
|
2287 8 bits per channel, this will strip the pixels down to 8-bit.
|
|
jpayne@68
|
2288
|
|
jpayne@68
|
2289 if (bit_depth == 16)
|
|
jpayne@68
|
2290 {
|
|
jpayne@68
|
2291 #if PNG_LIBPNG_VER >= 10504
|
|
jpayne@68
|
2292 png_set_scale_16(png_ptr);
|
|
jpayne@68
|
2293 #else
|
|
jpayne@68
|
2294 png_set_strip_16(png_ptr);
|
|
jpayne@68
|
2295 #endif
|
|
jpayne@68
|
2296 }
|
|
jpayne@68
|
2297
|
|
jpayne@68
|
2298 (The more accurate "png_set_scale_16()" API became available in libpng version
|
|
jpayne@68
|
2299 1.5.4).
|
|
jpayne@68
|
2300
|
|
jpayne@68
|
2301 If you need to process the alpha channel on the image separately from the image
|
|
jpayne@68
|
2302 data (for example if you convert it to a bitmap mask) it is possible to have
|
|
jpayne@68
|
2303 libpng strip the channel leaving just RGB or gray data:
|
|
jpayne@68
|
2304
|
|
jpayne@68
|
2305 if (color_type & PNG_COLOR_MASK_ALPHA)
|
|
jpayne@68
|
2306 png_set_strip_alpha(png_ptr);
|
|
jpayne@68
|
2307
|
|
jpayne@68
|
2308 If you strip the alpha channel you need to find some other way of dealing with
|
|
jpayne@68
|
2309 the information. If, instead, you want to convert the image to an opaque
|
|
jpayne@68
|
2310 version with no alpha channel use png_set_background; see below.
|
|
jpayne@68
|
2311
|
|
jpayne@68
|
2312 As of libpng version 1.5.2, almost all useful expansions are supported, the
|
|
jpayne@68
|
2313 major omissions are conversion of grayscale to indexed images (which can be
|
|
jpayne@68
|
2314 done trivially in the application) and conversion of indexed to grayscale (which
|
|
jpayne@68
|
2315 can be done by a trivial manipulation of the palette.)
|
|
jpayne@68
|
2316
|
|
jpayne@68
|
2317 In the following table, the 01 means grayscale with depth<8, 31 means
|
|
jpayne@68
|
2318 indexed with depth<8, other numerals represent the color type, "T" means
|
|
jpayne@68
|
2319 the tRNS chunk is present, A means an alpha channel is present, and O
|
|
jpayne@68
|
2320 means tRNS or alpha is present but all pixels in the image are opaque.
|
|
jpayne@68
|
2321
|
|
jpayne@68
|
2322 FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
|
|
jpayne@68
|
2323 TO
|
|
jpayne@68
|
2324 01 - [G] - - - - - - - - - - - - -
|
|
jpayne@68
|
2325 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q
|
|
jpayne@68
|
2326 0 1 G + . . G G G G G G B B GB GB
|
|
jpayne@68
|
2327 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt
|
|
jpayne@68
|
2328 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt
|
|
jpayne@68
|
2329 2 C P C C C + . . C - - CB CB B B
|
|
jpayne@68
|
2330 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt
|
|
jpayne@68
|
2331 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt
|
|
jpayne@68
|
2332 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q
|
|
jpayne@68
|
2333 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt
|
|
jpayne@68
|
2334 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt
|
|
jpayne@68
|
2335 4A lA G A T T GA GT GT GA GT GT + BA G GBA
|
|
jpayne@68
|
2336 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G
|
|
jpayne@68
|
2337 6A CA PA CA C C A T tT PA P P C CBA + BA
|
|
jpayne@68
|
2338 6O CA PBA CA C C A tT T PA P P CBA C BA +
|
|
jpayne@68
|
2339
|
|
jpayne@68
|
2340 Within the matrix,
|
|
jpayne@68
|
2341 "+" identifies entries where 'from' and 'to' are the same.
|
|
jpayne@68
|
2342 "-" means the transformation is not supported.
|
|
jpayne@68
|
2343 "." means nothing is necessary (a tRNS chunk can just be ignored).
|
|
jpayne@68
|
2344 "t" means the transformation is obtained by png_set_tRNS.
|
|
jpayne@68
|
2345 "A" means the transformation is obtained by png_set_add_alpha().
|
|
jpayne@68
|
2346 "X" means the transformation is obtained by png_set_expand().
|
|
jpayne@68
|
2347 "1" means the transformation is obtained by
|
|
jpayne@68
|
2348 png_set_expand_gray_1_2_4_to_8() (and by png_set_expand()
|
|
jpayne@68
|
2349 if there is no transparency in the original or the final
|
|
jpayne@68
|
2350 format).
|
|
jpayne@68
|
2351 "C" means the transformation is obtained by png_set_gray_to_rgb().
|
|
jpayne@68
|
2352 "G" means the transformation is obtained by png_set_rgb_to_gray().
|
|
jpayne@68
|
2353 "P" means the transformation is obtained by
|
|
jpayne@68
|
2354 png_set_expand_palette_to_rgb().
|
|
jpayne@68
|
2355 "p" means the transformation is obtained by png_set_packing().
|
|
jpayne@68
|
2356 "Q" means the transformation is obtained by png_set_quantize().
|
|
jpayne@68
|
2357 "T" means the transformation is obtained by
|
|
jpayne@68
|
2358 png_set_tRNS_to_alpha().
|
|
jpayne@68
|
2359 "B" means the transformation is obtained by
|
|
jpayne@68
|
2360 png_set_background(), or png_strip_alpha().
|
|
jpayne@68
|
2361
|
|
jpayne@68
|
2362 When an entry has multiple transforms listed all are required to cause the
|
|
jpayne@68
|
2363 right overall transformation. When two transforms are separated by a comma
|
|
jpayne@68
|
2364 either will do the job. When transforms are enclosed in [] the transform should
|
|
jpayne@68
|
2365 do the job but this is currently unimplemented - a different format will result
|
|
jpayne@68
|
2366 if the suggested transformations are used.
|
|
jpayne@68
|
2367
|
|
jpayne@68
|
2368 In PNG files, the alpha channel in an image
|
|
jpayne@68
|
2369 is the level of opacity. If you need the alpha channel in an image to
|
|
jpayne@68
|
2370 be the level of transparency instead of opacity, you can invert the
|
|
jpayne@68
|
2371 alpha channel (or the tRNS chunk data) after it's read, so that 0 is
|
|
jpayne@68
|
2372 fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
|
|
jpayne@68
|
2373 images) is fully transparent, with
|
|
jpayne@68
|
2374
|
|
jpayne@68
|
2375 png_set_invert_alpha(png_ptr);
|
|
jpayne@68
|
2376
|
|
jpayne@68
|
2377 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
|
|
jpayne@68
|
2378 they can, resulting in, for example, 8 pixels per byte for 1 bit
|
|
jpayne@68
|
2379 files. This code expands to 1 pixel per byte without changing the
|
|
jpayne@68
|
2380 values of the pixels:
|
|
jpayne@68
|
2381
|
|
jpayne@68
|
2382 if (bit_depth < 8)
|
|
jpayne@68
|
2383 png_set_packing(png_ptr);
|
|
jpayne@68
|
2384
|
|
jpayne@68
|
2385 PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
|
|
jpayne@68
|
2386 stored in a PNG image have been "scaled" or "shifted" up to the next
|
|
jpayne@68
|
2387 higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
|
|
jpayne@68
|
2388 to 8 bits/sample in the range [0, 255]). However, it is also possible
|
|
jpayne@68
|
2389 to convert the PNG pixel data back to the original bit depth of the
|
|
jpayne@68
|
2390 image. This call reduces the pixels back down to the original bit depth:
|
|
jpayne@68
|
2391
|
|
jpayne@68
|
2392 png_color_8p sig_bit;
|
|
jpayne@68
|
2393
|
|
jpayne@68
|
2394 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
|
|
jpayne@68
|
2395 png_set_shift(png_ptr, sig_bit);
|
|
jpayne@68
|
2396
|
|
jpayne@68
|
2397 PNG files store 3-color pixels in red, green, blue order. This code
|
|
jpayne@68
|
2398 changes the storage of the pixels to blue, green, red:
|
|
jpayne@68
|
2399
|
|
jpayne@68
|
2400 if (color_type == PNG_COLOR_TYPE_RGB ||
|
|
jpayne@68
|
2401 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|
jpayne@68
|
2402 png_set_bgr(png_ptr);
|
|
jpayne@68
|
2403
|
|
jpayne@68
|
2404 PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
|
|
jpayne@68
|
2405 into 4 or 8 bytes for windowing systems that need them in this format:
|
|
jpayne@68
|
2406
|
|
jpayne@68
|
2407 if (color_type == PNG_COLOR_TYPE_RGB)
|
|
jpayne@68
|
2408 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
|
|
jpayne@68
|
2409
|
|
jpayne@68
|
2410 where "filler" is the 8-bit or 16-bit number to fill with, and the location
|
|
jpayne@68
|
2411 is either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
|
|
jpayne@68
|
2412 you want the filler before the RGB or after. When filling an 8-bit pixel,
|
|
jpayne@68
|
2413 the least significant 8 bits of the number are used, if a 16-bit number is
|
|
jpayne@68
|
2414 supplied. This transformation does not affect images that already have full
|
|
jpayne@68
|
2415 alpha channels. To add an opaque alpha channel, use filler=0xffff and
|
|
jpayne@68
|
2416 PNG_FILLER_AFTER which will generate RGBA pixels.
|
|
jpayne@68
|
2417
|
|
jpayne@68
|
2418 Note that png_set_filler() does not change the color type. If you want
|
|
jpayne@68
|
2419 to do that, you can add a true alpha channel with
|
|
jpayne@68
|
2420
|
|
jpayne@68
|
2421 if (color_type == PNG_COLOR_TYPE_RGB ||
|
|
jpayne@68
|
2422 color_type == PNG_COLOR_TYPE_GRAY)
|
|
jpayne@68
|
2423 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
|
|
jpayne@68
|
2424
|
|
jpayne@68
|
2425 where "filler" contains the alpha value to assign to each pixel.
|
|
jpayne@68
|
2426 The png_set_add_alpha() function was added in libpng-1.2.7.
|
|
jpayne@68
|
2427
|
|
jpayne@68
|
2428 If you are reading an image with an alpha channel, and you need the
|
|
jpayne@68
|
2429 data as ARGB instead of the normal PNG format RGBA:
|
|
jpayne@68
|
2430
|
|
jpayne@68
|
2431 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|
jpayne@68
|
2432 png_set_swap_alpha(png_ptr);
|
|
jpayne@68
|
2433
|
|
jpayne@68
|
2434 For some uses, you may want a grayscale image to be represented as
|
|
jpayne@68
|
2435 RGB. This code will do that conversion:
|
|
jpayne@68
|
2436
|
|
jpayne@68
|
2437 if (color_type == PNG_COLOR_TYPE_GRAY ||
|
|
jpayne@68
|
2438 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
|
|
jpayne@68
|
2439 png_set_gray_to_rgb(png_ptr);
|
|
jpayne@68
|
2440
|
|
jpayne@68
|
2441 Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
|
|
jpayne@68
|
2442 with alpha.
|
|
jpayne@68
|
2443
|
|
jpayne@68
|
2444 if (color_type == PNG_COLOR_TYPE_RGB ||
|
|
jpayne@68
|
2445 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|
jpayne@68
|
2446 png_set_rgb_to_gray(png_ptr, error_action,
|
|
jpayne@68
|
2447 (double)red_weight, (double)green_weight);
|
|
jpayne@68
|
2448
|
|
jpayne@68
|
2449 error_action = 1: silently do the conversion
|
|
jpayne@68
|
2450
|
|
jpayne@68
|
2451 error_action = 2: issue a warning if the original
|
|
jpayne@68
|
2452 image has any pixel where
|
|
jpayne@68
|
2453 red != green or red != blue
|
|
jpayne@68
|
2454
|
|
jpayne@68
|
2455 error_action = 3: issue an error and abort the
|
|
jpayne@68
|
2456 conversion if the original
|
|
jpayne@68
|
2457 image has any pixel where
|
|
jpayne@68
|
2458 red != green or red != blue
|
|
jpayne@68
|
2459
|
|
jpayne@68
|
2460 red_weight: weight of red component
|
|
jpayne@68
|
2461
|
|
jpayne@68
|
2462 green_weight: weight of green component
|
|
jpayne@68
|
2463 If either weight is negative, default
|
|
jpayne@68
|
2464 weights are used.
|
|
jpayne@68
|
2465
|
|
jpayne@68
|
2466 In the corresponding fixed point API the red_weight and green_weight values are
|
|
jpayne@68
|
2467 simply scaled by 100,000:
|
|
jpayne@68
|
2468
|
|
jpayne@68
|
2469 png_set_rgb_to_gray(png_ptr, error_action,
|
|
jpayne@68
|
2470 (png_fixed_point)red_weight,
|
|
jpayne@68
|
2471 (png_fixed_point)green_weight);
|
|
jpayne@68
|
2472
|
|
jpayne@68
|
2473 If you have set error_action = 1 or 2, you can
|
|
jpayne@68
|
2474 later check whether the image really was gray, after processing
|
|
jpayne@68
|
2475 the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
|
|
jpayne@68
|
2476 It will return a png_byte that is zero if the image was gray or
|
|
jpayne@68
|
2477 1 if there were any non-gray pixels. Background and sBIT data
|
|
jpayne@68
|
2478 will be silently converted to grayscale, using the green channel
|
|
jpayne@68
|
2479 data for sBIT, regardless of the error_action setting.
|
|
jpayne@68
|
2480
|
|
jpayne@68
|
2481 The default values come from the PNG file cHRM chunk if present; otherwise, the
|
|
jpayne@68
|
2482 defaults correspond to the ITU-R recommendation 709, and also the sRGB color
|
|
jpayne@68
|
2483 space, as recommended in the Charles Poynton's Colour FAQ,
|
|
jpayne@68
|
2484 Copyright (c) 2006-11-28 Charles Poynton, in section 9:
|
|
jpayne@68
|
2485
|
|
jpayne@68
|
2486 <http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9>
|
|
jpayne@68
|
2487
|
|
jpayne@68
|
2488 Y = 0.2126 * R + 0.7152 * G + 0.0722 * B
|
|
jpayne@68
|
2489
|
|
jpayne@68
|
2490 Previous versions of this document, 1998 through 2002, recommended a slightly
|
|
jpayne@68
|
2491 different formula:
|
|
jpayne@68
|
2492
|
|
jpayne@68
|
2493 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
|
|
jpayne@68
|
2494
|
|
jpayne@68
|
2495 Libpng uses an integer approximation:
|
|
jpayne@68
|
2496
|
|
jpayne@68
|
2497 Y = (6968 * R + 23434 * G + 2366 * B)/32768
|
|
jpayne@68
|
2498
|
|
jpayne@68
|
2499 The calculation is done in a linear colorspace, if the image gamma
|
|
jpayne@68
|
2500 can be determined.
|
|
jpayne@68
|
2501
|
|
jpayne@68
|
2502 The png_set_background() function has been described already; it tells libpng to
|
|
jpayne@68
|
2503 composite images with alpha or simple transparency against the supplied
|
|
jpayne@68
|
2504 background color. For compatibility with versions of libpng earlier than
|
|
jpayne@68
|
2505 libpng-1.5.4 it is recommended that you call the function after reading the file
|
|
jpayne@68
|
2506 header, even if you don't want to use the color in a bKGD chunk, if one exists.
|
|
jpayne@68
|
2507
|
|
jpayne@68
|
2508 If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
|
|
jpayne@68
|
2509 you may use this color, or supply another color more suitable for
|
|
jpayne@68
|
2510 the current display (e.g., the background color from a web page). You
|
|
jpayne@68
|
2511 need to tell libpng how the color is represented, both the format of the
|
|
jpayne@68
|
2512 component values in the color (the number of bits) and the gamma encoding of the
|
|
jpayne@68
|
2513 color. The function takes two arguments, background_gamma_mode and need_expand
|
|
jpayne@68
|
2514 to convey this information; however, only two combinations are likely to be
|
|
jpayne@68
|
2515 useful:
|
|
jpayne@68
|
2516
|
|
jpayne@68
|
2517 png_color_16 my_background;
|
|
jpayne@68
|
2518 png_color_16p image_background;
|
|
jpayne@68
|
2519
|
|
jpayne@68
|
2520 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
|
|
jpayne@68
|
2521 png_set_background(png_ptr, image_background,
|
|
jpayne@68
|
2522 PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1);
|
|
jpayne@68
|
2523 else
|
|
jpayne@68
|
2524 png_set_background(png_ptr, &my_background,
|
|
jpayne@68
|
2525 PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1);
|
|
jpayne@68
|
2526
|
|
jpayne@68
|
2527 The second call was described above - my_background is in the format of the
|
|
jpayne@68
|
2528 final, display, output produced by libpng. Because you now know the format of
|
|
jpayne@68
|
2529 the PNG it is possible to avoid the need to choose either 8-bit or 16-bit
|
|
jpayne@68
|
2530 output and to retain palette images (the palette colors will be modified
|
|
jpayne@68
|
2531 appropriately and the tRNS chunk removed.) However, if you are doing this,
|
|
jpayne@68
|
2532 take great care not to ask for transformations without checking first that
|
|
jpayne@68
|
2533 they apply!
|
|
jpayne@68
|
2534
|
|
jpayne@68
|
2535 In the first call the background color has the original bit depth and color type
|
|
jpayne@68
|
2536 of the PNG file. So, for palette images the color is supplied as a palette
|
|
jpayne@68
|
2537 index and for low bit greyscale images the color is a reduced bit value in
|
|
jpayne@68
|
2538 image_background->gray.
|
|
jpayne@68
|
2539
|
|
jpayne@68
|
2540 If you didn't call png_set_gamma() before reading the file header, for example
|
|
jpayne@68
|
2541 if you need your code to remain compatible with older versions of libpng prior
|
|
jpayne@68
|
2542 to libpng-1.5.4, this is the place to call it.
|
|
jpayne@68
|
2543
|
|
jpayne@68
|
2544 Do not call it if you called png_set_alpha_mode(); doing so will damage the
|
|
jpayne@68
|
2545 settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is
|
|
jpayne@68
|
2546 supported then you can certainly do png_set_gamma() before reading the PNG
|
|
jpayne@68
|
2547 header.)
|
|
jpayne@68
|
2548
|
|
jpayne@68
|
2549 This API unconditionally sets the screen and file gamma values, so it will
|
|
jpayne@68
|
2550 override the value in the PNG file unless it is called before the PNG file
|
|
jpayne@68
|
2551 reading starts. For this reason you must always call it with the PNG file
|
|
jpayne@68
|
2552 value when you call it in this position:
|
|
jpayne@68
|
2553
|
|
jpayne@68
|
2554 if (png_get_gAMA(png_ptr, info_ptr, &file_gamma))
|
|
jpayne@68
|
2555 png_set_gamma(png_ptr, screen_gamma, file_gamma);
|
|
jpayne@68
|
2556
|
|
jpayne@68
|
2557 else
|
|
jpayne@68
|
2558 png_set_gamma(png_ptr, screen_gamma, 0.45455);
|
|
jpayne@68
|
2559
|
|
jpayne@68
|
2560 If you need to reduce an RGB file to a paletted file, or if a paletted
|
|
jpayne@68
|
2561 file has more entries than will fit on your screen, png_set_quantize()
|
|
jpayne@68
|
2562 will do that. Note that this is a simple match quantization that merely
|
|
jpayne@68
|
2563 finds the closest color available. This should work fairly well with
|
|
jpayne@68
|
2564 optimized palettes, but fairly badly with linear color cubes. If you
|
|
jpayne@68
|
2565 pass a palette that is larger than maximum_colors, the file will
|
|
jpayne@68
|
2566 reduce the number of colors in the palette so it will fit into
|
|
jpayne@68
|
2567 maximum_colors. If there is a histogram, libpng will use it to make
|
|
jpayne@68
|
2568 more intelligent choices when reducing the palette. If there is no
|
|
jpayne@68
|
2569 histogram, it may not do as good a job.
|
|
jpayne@68
|
2570
|
|
jpayne@68
|
2571 if (color_type & PNG_COLOR_MASK_COLOR)
|
|
jpayne@68
|
2572 {
|
|
jpayne@68
|
2573 if (png_get_valid(png_ptr, info_ptr,
|
|
jpayne@68
|
2574 PNG_INFO_PLTE))
|
|
jpayne@68
|
2575 {
|
|
jpayne@68
|
2576 png_uint_16p histogram = NULL;
|
|
jpayne@68
|
2577
|
|
jpayne@68
|
2578 png_get_hIST(png_ptr, info_ptr,
|
|
jpayne@68
|
2579 &histogram);
|
|
jpayne@68
|
2580 png_set_quantize(png_ptr, palette, num_palette,
|
|
jpayne@68
|
2581 max_screen_colors, histogram, 1);
|
|
jpayne@68
|
2582 }
|
|
jpayne@68
|
2583
|
|
jpayne@68
|
2584 else
|
|
jpayne@68
|
2585 {
|
|
jpayne@68
|
2586 png_color std_color_cube[MAX_SCREEN_COLORS] =
|
|
jpayne@68
|
2587 { ... colors ... };
|
|
jpayne@68
|
2588
|
|
jpayne@68
|
2589 png_set_quantize(png_ptr, std_color_cube,
|
|
jpayne@68
|
2590 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
|
|
jpayne@68
|
2591 NULL,0);
|
|
jpayne@68
|
2592 }
|
|
jpayne@68
|
2593 }
|
|
jpayne@68
|
2594
|
|
jpayne@68
|
2595 PNG files describe monochrome as black being zero and white being one.
|
|
jpayne@68
|
2596 The following code will reverse this (make black be one and white be
|
|
jpayne@68
|
2597 zero):
|
|
jpayne@68
|
2598
|
|
jpayne@68
|
2599 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
|
|
jpayne@68
|
2600 png_set_invert_mono(png_ptr);
|
|
jpayne@68
|
2601
|
|
jpayne@68
|
2602 This function can also be used to invert grayscale and gray-alpha images:
|
|
jpayne@68
|
2603
|
|
jpayne@68
|
2604 if (color_type == PNG_COLOR_TYPE_GRAY ||
|
|
jpayne@68
|
2605 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
|
|
jpayne@68
|
2606 png_set_invert_mono(png_ptr);
|
|
jpayne@68
|
2607
|
|
jpayne@68
|
2608 PNG files store 16-bit pixels in network byte order (big-endian,
|
|
jpayne@68
|
2609 ie. most significant bits first). This code changes the storage to the
|
|
jpayne@68
|
2610 other way (little-endian, i.e. least significant bits first, the
|
|
jpayne@68
|
2611 way PCs store them):
|
|
jpayne@68
|
2612
|
|
jpayne@68
|
2613 if (bit_depth == 16)
|
|
jpayne@68
|
2614 png_set_swap(png_ptr);
|
|
jpayne@68
|
2615
|
|
jpayne@68
|
2616 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
|
|
jpayne@68
|
2617 need to change the order the pixels are packed into bytes, you can use:
|
|
jpayne@68
|
2618
|
|
jpayne@68
|
2619 if (bit_depth < 8)
|
|
jpayne@68
|
2620 png_set_packswap(png_ptr);
|
|
jpayne@68
|
2621
|
|
jpayne@68
|
2622 Finally, you can write your own transformation function if none of
|
|
jpayne@68
|
2623 the existing ones meets your needs. This is done by setting a callback
|
|
jpayne@68
|
2624 with
|
|
jpayne@68
|
2625
|
|
jpayne@68
|
2626 png_set_read_user_transform_fn(png_ptr,
|
|
jpayne@68
|
2627 read_transform_fn);
|
|
jpayne@68
|
2628
|
|
jpayne@68
|
2629 You must supply the function
|
|
jpayne@68
|
2630
|
|
jpayne@68
|
2631 void read_transform_fn(png_structp png_ptr, png_row_infop
|
|
jpayne@68
|
2632 row_info, png_bytep data)
|
|
jpayne@68
|
2633
|
|
jpayne@68
|
2634 See pngtest.c for a working example. Your function will be called
|
|
jpayne@68
|
2635 after all of the other transformations have been processed. Take care with
|
|
jpayne@68
|
2636 interlaced images if you do the interlace yourself - the width of the row is the
|
|
jpayne@68
|
2637 width in 'row_info', not the overall image width.
|
|
jpayne@68
|
2638
|
|
jpayne@68
|
2639 If supported, libpng provides two information routines that you can use to find
|
|
jpayne@68
|
2640 where you are in processing the image:
|
|
jpayne@68
|
2641
|
|
jpayne@68
|
2642 png_get_current_pass_number(png_structp png_ptr);
|
|
jpayne@68
|
2643 png_get_current_row_number(png_structp png_ptr);
|
|
jpayne@68
|
2644
|
|
jpayne@68
|
2645 Don't try using these outside a transform callback - firstly they are only
|
|
jpayne@68
|
2646 supported if user transforms are supported, secondly they may well return
|
|
jpayne@68
|
2647 unexpected results unless the row is actually being processed at the moment they
|
|
jpayne@68
|
2648 are called.
|
|
jpayne@68
|
2649
|
|
jpayne@68
|
2650 With interlaced
|
|
jpayne@68
|
2651 images the value returned is the row in the input sub-image image. Use
|
|
jpayne@68
|
2652 PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
|
|
jpayne@68
|
2653 find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
|
|
jpayne@68
|
2654
|
|
jpayne@68
|
2655 The discussion of interlace handling above contains more information on how to
|
|
jpayne@68
|
2656 use these values.
|
|
jpayne@68
|
2657
|
|
jpayne@68
|
2658 You can also set up a pointer to a user structure for use by your
|
|
jpayne@68
|
2659 callback function, and you can inform libpng that your transform
|
|
jpayne@68
|
2660 function will change the number of channels or bit depth with the
|
|
jpayne@68
|
2661 function
|
|
jpayne@68
|
2662
|
|
jpayne@68
|
2663 png_set_user_transform_info(png_ptr, user_ptr,
|
|
jpayne@68
|
2664 user_depth, user_channels);
|
|
jpayne@68
|
2665
|
|
jpayne@68
|
2666 The user's application, not libpng, is responsible for allocating and
|
|
jpayne@68
|
2667 freeing any memory required for the user structure.
|
|
jpayne@68
|
2668
|
|
jpayne@68
|
2669 You can retrieve the pointer via the function
|
|
jpayne@68
|
2670 png_get_user_transform_ptr(). For example:
|
|
jpayne@68
|
2671
|
|
jpayne@68
|
2672 voidp read_user_transform_ptr =
|
|
jpayne@68
|
2673 png_get_user_transform_ptr(png_ptr);
|
|
jpayne@68
|
2674
|
|
jpayne@68
|
2675 The last thing to handle is interlacing; this is covered in detail below,
|
|
jpayne@68
|
2676 but you must call the function here if you want libpng to handle expansion
|
|
jpayne@68
|
2677 of the interlaced image.
|
|
jpayne@68
|
2678
|
|
jpayne@68
|
2679 number_of_passes = png_set_interlace_handling(png_ptr);
|
|
jpayne@68
|
2680
|
|
jpayne@68
|
2681 After setting the transformations, libpng can update your png_info
|
|
jpayne@68
|
2682 structure to reflect any transformations you've requested with this
|
|
jpayne@68
|
2683 call.
|
|
jpayne@68
|
2684
|
|
jpayne@68
|
2685 png_read_update_info(png_ptr, info_ptr);
|
|
jpayne@68
|
2686
|
|
jpayne@68
|
2687 This is most useful to update the info structure's rowbytes
|
|
jpayne@68
|
2688 field so you can use it to allocate your image memory. This function
|
|
jpayne@68
|
2689 will also update your palette with the correct screen_gamma and
|
|
jpayne@68
|
2690 background if these have been given with the calls above. You may
|
|
jpayne@68
|
2691 only call png_read_update_info() once with a particular info_ptr.
|
|
jpayne@68
|
2692
|
|
jpayne@68
|
2693 After you call png_read_update_info(), you can allocate any
|
|
jpayne@68
|
2694 memory you need to hold the image. The row data is simply
|
|
jpayne@68
|
2695 raw byte data for all forms of images. As the actual allocation
|
|
jpayne@68
|
2696 varies among applications, no example will be given. If you
|
|
jpayne@68
|
2697 are allocating one large chunk, you will need to build an
|
|
jpayne@68
|
2698 array of pointers to each row, as it will be needed for some
|
|
jpayne@68
|
2699 of the functions below.
|
|
jpayne@68
|
2700
|
|
jpayne@68
|
2701 Be sure that your platform can allocate the buffer that you'll need.
|
|
jpayne@68
|
2702 libpng internally checks for oversize width, but you'll need to
|
|
jpayne@68
|
2703 do your own check for number_of_rows*width*pixel_size if you are using
|
|
jpayne@68
|
2704 a multiple-row buffer:
|
|
jpayne@68
|
2705
|
|
jpayne@68
|
2706 /* Guard against integer overflow */
|
|
jpayne@68
|
2707 if (number_of_rows > PNG_SIZE_MAX/(width*pixel_size))
|
|
jpayne@68
|
2708 png_error(png_ptr, "image_data buffer would be too large");
|
|
jpayne@68
|
2709
|
|
jpayne@68
|
2710 Remember: Before you call png_read_update_info(), the png_get_*()
|
|
jpayne@68
|
2711 functions return the values corresponding to the original PNG image.
|
|
jpayne@68
|
2712 After you call png_read_update_info the values refer to the image
|
|
jpayne@68
|
2713 that libpng will output. Consequently you must call all the png_set_
|
|
jpayne@68
|
2714 functions before you call png_read_update_info(). This is particularly
|
|
jpayne@68
|
2715 important for png_set_interlace_handling() - if you are going to call
|
|
jpayne@68
|
2716 png_read_update_info() you must call png_set_interlace_handling() before
|
|
jpayne@68
|
2717 it unless you want to receive interlaced output.
|
|
jpayne@68
|
2718
|
|
jpayne@68
|
2719 .SS Reading image data
|
|
jpayne@68
|
2720
|
|
jpayne@68
|
2721 After you've allocated memory, you can read the image data.
|
|
jpayne@68
|
2722 The simplest way to do this is in one function call. If you are
|
|
jpayne@68
|
2723 allocating enough memory to hold the whole image, you can just
|
|
jpayne@68
|
2724 call png_read_image() and libpng will read in all the image data
|
|
jpayne@68
|
2725 and put it in the memory area supplied. You will need to pass in
|
|
jpayne@68
|
2726 an array of pointers to each row.
|
|
jpayne@68
|
2727
|
|
jpayne@68
|
2728 This function automatically handles interlacing, so you don't
|
|
jpayne@68
|
2729 need to call png_set_interlace_handling() (unless you call
|
|
jpayne@68
|
2730 png_read_update_info()) or call this function multiple times, or any
|
|
jpayne@68
|
2731 of that other stuff necessary with png_read_rows().
|
|
jpayne@68
|
2732
|
|
jpayne@68
|
2733 png_read_image(png_ptr, row_pointers);
|
|
jpayne@68
|
2734
|
|
jpayne@68
|
2735 where row_pointers is:
|
|
jpayne@68
|
2736
|
|
jpayne@68
|
2737 png_bytep row_pointers[height];
|
|
jpayne@68
|
2738
|
|
jpayne@68
|
2739 You can point to void or char or whatever you use for pixels.
|
|
jpayne@68
|
2740
|
|
jpayne@68
|
2741 If you don't want to read in the whole image at once, you can
|
|
jpayne@68
|
2742 use png_read_rows() instead. If there is no interlacing (check
|
|
jpayne@68
|
2743 interlace_type == PNG_INTERLACE_NONE), this is simple:
|
|
jpayne@68
|
2744
|
|
jpayne@68
|
2745 png_read_rows(png_ptr, row_pointers, NULL,
|
|
jpayne@68
|
2746 number_of_rows);
|
|
jpayne@68
|
2747
|
|
jpayne@68
|
2748 where row_pointers is the same as in the png_read_image() call.
|
|
jpayne@68
|
2749
|
|
jpayne@68
|
2750 If you are doing this just one row at a time, you can do this with
|
|
jpayne@68
|
2751 a single row_pointer instead of an array of row_pointers:
|
|
jpayne@68
|
2752
|
|
jpayne@68
|
2753 png_bytep row_pointer = row;
|
|
jpayne@68
|
2754 png_read_row(png_ptr, row_pointer, NULL);
|
|
jpayne@68
|
2755
|
|
jpayne@68
|
2756 If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
|
|
jpayne@68
|
2757 get somewhat harder. The only current (PNG Specification version 1.2)
|
|
jpayne@68
|
2758 interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7);
|
|
jpayne@68
|
2759 a somewhat complicated 2D interlace scheme, known as Adam7, that
|
|
jpayne@68
|
2760 breaks down an image into seven smaller images of varying size, based
|
|
jpayne@68
|
2761 on an 8x8 grid. This number is defined (from libpng 1.5) as
|
|
jpayne@68
|
2762 PNG_INTERLACE_ADAM7_PASSES in png.h
|
|
jpayne@68
|
2763
|
|
jpayne@68
|
2764 libpng can fill out those images or it can give them to you "as is".
|
|
jpayne@68
|
2765 It is almost always better to have libpng handle the interlacing for you.
|
|
jpayne@68
|
2766 If you want the images filled out, there are two ways to do that. The one
|
|
jpayne@68
|
2767 mentioned in the PNG specification is to expand each pixel to cover
|
|
jpayne@68
|
2768 those pixels that have not been read yet (the "rectangle" method).
|
|
jpayne@68
|
2769 This results in a blocky image for the first pass, which gradually
|
|
jpayne@68
|
2770 smooths out as more pixels are read. The other method is the "sparkle"
|
|
jpayne@68
|
2771 method, where pixels are drawn only in their final locations, with the
|
|
jpayne@68
|
2772 rest of the image remaining whatever colors they were initialized to
|
|
jpayne@68
|
2773 before the start of the read. The first method usually looks better,
|
|
jpayne@68
|
2774 but tends to be slower, as there are more pixels to put in the rows.
|
|
jpayne@68
|
2775
|
|
jpayne@68
|
2776 If, as is likely, you want libpng to expand the images, call this before
|
|
jpayne@68
|
2777 calling png_start_read_image() or png_read_update_info():
|
|
jpayne@68
|
2778
|
|
jpayne@68
|
2779 if (interlace_type == PNG_INTERLACE_ADAM7)
|
|
jpayne@68
|
2780 number_of_passes
|
|
jpayne@68
|
2781 = png_set_interlace_handling(png_ptr);
|
|
jpayne@68
|
2782
|
|
jpayne@68
|
2783 This will return the number of passes needed. Currently, this is seven,
|
|
jpayne@68
|
2784 but may change if another interlace type is added. This function can be
|
|
jpayne@68
|
2785 called even if the file is not interlaced, where it will return one pass.
|
|
jpayne@68
|
2786 You then need to read the whole image 'number_of_passes' times. Each time
|
|
jpayne@68
|
2787 will distribute the pixels from the current pass to the correct place in
|
|
jpayne@68
|
2788 the output image, so you need to supply the same rows to png_read_rows in
|
|
jpayne@68
|
2789 each pass.
|
|
jpayne@68
|
2790
|
|
jpayne@68
|
2791 If you are not going to display the image after each pass, but are
|
|
jpayne@68
|
2792 going to wait until the entire image is read in, use the sparkle
|
|
jpayne@68
|
2793 effect. This effect is faster and the end result of either method
|
|
jpayne@68
|
2794 is exactly the same. If you are planning on displaying the image
|
|
jpayne@68
|
2795 after each pass, the "rectangle" effect is generally considered the
|
|
jpayne@68
|
2796 better looking one.
|
|
jpayne@68
|
2797
|
|
jpayne@68
|
2798 If you only want the "sparkle" effect, just call png_read_row() or
|
|
jpayne@68
|
2799 png_read_rows() as
|
|
jpayne@68
|
2800 normal, with the third parameter NULL. Make sure you make pass over
|
|
jpayne@68
|
2801 the image number_of_passes times, and you don't change the data in the
|
|
jpayne@68
|
2802 rows between calls. You can change the locations of the data, just
|
|
jpayne@68
|
2803 not the data. Each pass only writes the pixels appropriate for that
|
|
jpayne@68
|
2804 pass, and assumes the data from previous passes is still valid.
|
|
jpayne@68
|
2805
|
|
jpayne@68
|
2806 png_read_rows(png_ptr, row_pointers, NULL,
|
|
jpayne@68
|
2807 number_of_rows);
|
|
jpayne@68
|
2808 or
|
|
jpayne@68
|
2809 png_read_row(png_ptr, row_pointers, NULL);
|
|
jpayne@68
|
2810
|
|
jpayne@68
|
2811 If you only want the first effect (the rectangles), do the same as
|
|
jpayne@68
|
2812 before except pass the row buffer in the third parameter, and leave
|
|
jpayne@68
|
2813 the second parameter NULL.
|
|
jpayne@68
|
2814
|
|
jpayne@68
|
2815 png_read_rows(png_ptr, NULL, row_pointers,
|
|
jpayne@68
|
2816 number_of_rows);
|
|
jpayne@68
|
2817 or
|
|
jpayne@68
|
2818 png_read_row(png_ptr, NULL, row_pointers);
|
|
jpayne@68
|
2819
|
|
jpayne@68
|
2820 If you don't want libpng to handle the interlacing details, just call
|
|
jpayne@68
|
2821 png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.
|
|
jpayne@68
|
2822 Each of the images is a valid image by itself; however, you will almost
|
|
jpayne@68
|
2823 certainly need to distribute the pixels from each sub-image to the
|
|
jpayne@68
|
2824 correct place. This is where everything gets very tricky.
|
|
jpayne@68
|
2825
|
|
jpayne@68
|
2826 If you want to retrieve the separate images you must pass the correct
|
|
jpayne@68
|
2827 number of rows to each successive call of png_read_rows(). The calculation
|
|
jpayne@68
|
2828 gets pretty complicated for small images, where some sub-images may
|
|
jpayne@68
|
2829 not even exist because either their width or height ends up zero.
|
|
jpayne@68
|
2830 libpng provides two macros to help you in 1.5 and later versions:
|
|
jpayne@68
|
2831
|
|
jpayne@68
|
2832 png_uint_32 width = PNG_PASS_COLS(image_width, pass_number);
|
|
jpayne@68
|
2833 png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number);
|
|
jpayne@68
|
2834
|
|
jpayne@68
|
2835 Respectively these tell you the width and height of the sub-image
|
|
jpayne@68
|
2836 corresponding to the numbered pass. 'pass' is in in the range 0 to 6 -
|
|
jpayne@68
|
2837 this can be confusing because the specification refers to the same passes
|
|
jpayne@68
|
2838 as 1 to 7! Be careful, you must check both the width and height before
|
|
jpayne@68
|
2839 calling png_read_rows() and not call it for that pass if either is zero.
|
|
jpayne@68
|
2840
|
|
jpayne@68
|
2841 You can, of course, read each sub-image row by row. If you want to
|
|
jpayne@68
|
2842 produce optimal code to make a pixel-by-pixel transformation of an
|
|
jpayne@68
|
2843 interlaced image this is the best approach; read each row of each pass,
|
|
jpayne@68
|
2844 transform it, and write it out to a new interlaced image.
|
|
jpayne@68
|
2845
|
|
jpayne@68
|
2846 If you want to de-interlace the image yourself libpng provides further
|
|
jpayne@68
|
2847 macros to help that tell you where to place the pixels in the output image.
|
|
jpayne@68
|
2848 Because the interlacing scheme is rectangular - sub-image pixels are always
|
|
jpayne@68
|
2849 arranged on a rectangular grid - all you need to know for each pass is the
|
|
jpayne@68
|
2850 starting column and row in the output image of the first pixel plus the
|
|
jpayne@68
|
2851 spacing between each pixel. As of libpng 1.5 there are four macros to
|
|
jpayne@68
|
2852 retrieve this information:
|
|
jpayne@68
|
2853
|
|
jpayne@68
|
2854 png_uint_32 x = PNG_PASS_START_COL(pass);
|
|
jpayne@68
|
2855 png_uint_32 y = PNG_PASS_START_ROW(pass);
|
|
jpayne@68
|
2856 png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass);
|
|
jpayne@68
|
2857 png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass);
|
|
jpayne@68
|
2858
|
|
jpayne@68
|
2859 These allow you to write the obvious loop:
|
|
jpayne@68
|
2860
|
|
jpayne@68
|
2861 png_uint_32 input_y = 0;
|
|
jpayne@68
|
2862 png_uint_32 output_y = PNG_PASS_START_ROW(pass);
|
|
jpayne@68
|
2863
|
|
jpayne@68
|
2864 while (output_y < output_image_height)
|
|
jpayne@68
|
2865 {
|
|
jpayne@68
|
2866 png_uint_32 input_x = 0;
|
|
jpayne@68
|
2867 png_uint_32 output_x = PNG_PASS_START_COL(pass);
|
|
jpayne@68
|
2868
|
|
jpayne@68
|
2869 while (output_x < output_image_width)
|
|
jpayne@68
|
2870 {
|
|
jpayne@68
|
2871 image[output_y][output_x] =
|
|
jpayne@68
|
2872 subimage[pass][input_y][input_x++];
|
|
jpayne@68
|
2873
|
|
jpayne@68
|
2874 output_x += xStep;
|
|
jpayne@68
|
2875 }
|
|
jpayne@68
|
2876
|
|
jpayne@68
|
2877 ++input_y;
|
|
jpayne@68
|
2878 output_y += yStep;
|
|
jpayne@68
|
2879 }
|
|
jpayne@68
|
2880
|
|
jpayne@68
|
2881 Notice that the steps between successive output rows and columns are
|
|
jpayne@68
|
2882 returned as shifts. This is possible because the pixels in the subimages
|
|
jpayne@68
|
2883 are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original
|
|
jpayne@68
|
2884 image. In practice you may need to directly calculate the output coordinate
|
|
jpayne@68
|
2885 given an input coordinate. libpng provides two further macros for this
|
|
jpayne@68
|
2886 purpose:
|
|
jpayne@68
|
2887
|
|
jpayne@68
|
2888 png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass);
|
|
jpayne@68
|
2889 png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass);
|
|
jpayne@68
|
2890
|
|
jpayne@68
|
2891 Finally a pair of macros are provided to tell you if a particular image
|
|
jpayne@68
|
2892 row or column appears in a given pass:
|
|
jpayne@68
|
2893
|
|
jpayne@68
|
2894 int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass);
|
|
jpayne@68
|
2895 int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass);
|
|
jpayne@68
|
2896
|
|
jpayne@68
|
2897 Bear in mind that you will probably also need to check the width and height
|
|
jpayne@68
|
2898 of the pass in addition to the above to be sure the pass even exists!
|
|
jpayne@68
|
2899
|
|
jpayne@68
|
2900 With any luck you are convinced by now that you don't want to do your own
|
|
jpayne@68
|
2901 interlace handling. In reality normally the only good reason for doing this
|
|
jpayne@68
|
2902 is if you are processing PNG files on a pixel-by-pixel basis and don't want
|
|
jpayne@68
|
2903 to load the whole file into memory when it is interlaced.
|
|
jpayne@68
|
2904
|
|
jpayne@68
|
2905 libpng includes a test program, pngvalid, that illustrates reading and
|
|
jpayne@68
|
2906 writing of interlaced images. If you can't get interlacing to work in your
|
|
jpayne@68
|
2907 code and don't want to leave it to libpng (the recommended approach), see
|
|
jpayne@68
|
2908 how pngvalid.c does it.
|
|
jpayne@68
|
2909
|
|
jpayne@68
|
2910 .SS Finishing a sequential read
|
|
jpayne@68
|
2911
|
|
jpayne@68
|
2912 After you are finished reading the image through the
|
|
jpayne@68
|
2913 low-level interface, you can finish reading the file.
|
|
jpayne@68
|
2914
|
|
jpayne@68
|
2915 If you want to use a different crc action for handling CRC errors in
|
|
jpayne@68
|
2916 chunks after the image data, you can call png_set_crc_action()
|
|
jpayne@68
|
2917 again at this point.
|
|
jpayne@68
|
2918
|
|
jpayne@68
|
2919 If you are interested in comments or time, which may be stored either
|
|
jpayne@68
|
2920 before or after the image data, you should pass the separate png_info
|
|
jpayne@68
|
2921 struct if you want to keep the comments from before and after the image
|
|
jpayne@68
|
2922 separate.
|
|
jpayne@68
|
2923
|
|
jpayne@68
|
2924 png_infop end_info = png_create_info_struct(png_ptr);
|
|
jpayne@68
|
2925
|
|
jpayne@68
|
2926 if (!end_info)
|
|
jpayne@68
|
2927 {
|
|
jpayne@68
|
2928 png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
|
|
jpayne@68
|
2929 return ERROR;
|
|
jpayne@68
|
2930 }
|
|
jpayne@68
|
2931
|
|
jpayne@68
|
2932 png_read_end(png_ptr, end_info);
|
|
jpayne@68
|
2933
|
|
jpayne@68
|
2934 If you are not interested, you should still call png_read_end()
|
|
jpayne@68
|
2935 but you can pass NULL, avoiding the need to create an end_info structure.
|
|
jpayne@68
|
2936 If you do this, libpng will not process any chunks after IDAT other than
|
|
jpayne@68
|
2937 skipping over them and perhaps (depending on whether you have called
|
|
jpayne@68
|
2938 png_set_crc_action) checking their CRCs while looking for the IEND chunk.
|
|
jpayne@68
|
2939
|
|
jpayne@68
|
2940 png_read_end(png_ptr, NULL);
|
|
jpayne@68
|
2941
|
|
jpayne@68
|
2942 If you don't call png_read_end(), then your file pointer will be
|
|
jpayne@68
|
2943 left pointing to the first chunk after the last IDAT, which is probably
|
|
jpayne@68
|
2944 not what you want if you expect to read something beyond the end of
|
|
jpayne@68
|
2945 the PNG datastream.
|
|
jpayne@68
|
2946
|
|
jpayne@68
|
2947 When you are done, you can free all memory allocated by libpng like this:
|
|
jpayne@68
|
2948
|
|
jpayne@68
|
2949 png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
|
|
jpayne@68
|
2950
|
|
jpayne@68
|
2951 or, if you didn't create an end_info structure,
|
|
jpayne@68
|
2952
|
|
jpayne@68
|
2953 png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
|
|
jpayne@68
|
2954
|
|
jpayne@68
|
2955 It is also possible to individually free the info_ptr members that
|
|
jpayne@68
|
2956 point to libpng-allocated storage with the following function:
|
|
jpayne@68
|
2957
|
|
jpayne@68
|
2958 png_free_data(png_ptr, info_ptr, mask, seq)
|
|
jpayne@68
|
2959
|
|
jpayne@68
|
2960 mask - identifies data to be freed, a mask
|
|
jpayne@68
|
2961 containing the bitwise OR of one or
|
|
jpayne@68
|
2962 more of
|
|
jpayne@68
|
2963 PNG_FREE_PLTE, PNG_FREE_TRNS,
|
|
jpayne@68
|
2964 PNG_FREE_HIST, PNG_FREE_ICCP,
|
|
jpayne@68
|
2965 PNG_FREE_PCAL, PNG_FREE_ROWS,
|
|
jpayne@68
|
2966 PNG_FREE_SCAL, PNG_FREE_SPLT,
|
|
jpayne@68
|
2967 PNG_FREE_TEXT, PNG_FREE_UNKN,
|
|
jpayne@68
|
2968 or simply PNG_FREE_ALL
|
|
jpayne@68
|
2969
|
|
jpayne@68
|
2970 seq - sequence number of item to be freed
|
|
jpayne@68
|
2971 (\-1 for all items)
|
|
jpayne@68
|
2972
|
|
jpayne@68
|
2973 This function may be safely called when the relevant storage has
|
|
jpayne@68
|
2974 already been freed, or has not yet been allocated, or was allocated
|
|
jpayne@68
|
2975 by the user and not by libpng, and will in those cases do nothing.
|
|
jpayne@68
|
2976 The "seq" parameter is ignored if only one item of the selected data
|
|
jpayne@68
|
2977 type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items
|
|
jpayne@68
|
2978 are allowed for the data type identified in the mask, such as text or
|
|
jpayne@68
|
2979 sPLT, only the n'th item in the structure is freed, where n is "seq".
|
|
jpayne@68
|
2980
|
|
jpayne@68
|
2981 The default behavior is only to free data that was allocated internally
|
|
jpayne@68
|
2982 by libpng. This can be changed, so that libpng will not free the data,
|
|
jpayne@68
|
2983 or so that it will free data that was allocated by the user with png_malloc()
|
|
jpayne@68
|
2984 or png_calloc() and passed in via a png_set_*() function, with
|
|
jpayne@68
|
2985
|
|
jpayne@68
|
2986 png_data_freer(png_ptr, info_ptr, freer, mask)
|
|
jpayne@68
|
2987
|
|
jpayne@68
|
2988 freer - one of
|
|
jpayne@68
|
2989 PNG_DESTROY_WILL_FREE_DATA
|
|
jpayne@68
|
2990 PNG_SET_WILL_FREE_DATA
|
|
jpayne@68
|
2991 PNG_USER_WILL_FREE_DATA
|
|
jpayne@68
|
2992
|
|
jpayne@68
|
2993 mask - which data elements are affected
|
|
jpayne@68
|
2994 same choices as in png_free_data()
|
|
jpayne@68
|
2995
|
|
jpayne@68
|
2996 This function only affects data that has already been allocated.
|
|
jpayne@68
|
2997 You can call this function after reading the PNG data but before calling
|
|
jpayne@68
|
2998 any png_set_*() functions, to control whether the user or the png_set_*()
|
|
jpayne@68
|
2999 function is responsible for freeing any existing data that might be present,
|
|
jpayne@68
|
3000 and again after the png_set_*() functions to control whether the user
|
|
jpayne@68
|
3001 or png_destroy_*() is supposed to free the data. When the user assumes
|
|
jpayne@68
|
3002 responsibility for libpng-allocated data, the application must use
|
|
jpayne@68
|
3003 png_free() to free it, and when the user transfers responsibility to libpng
|
|
jpayne@68
|
3004 for data that the user has allocated, the user must have used png_malloc()
|
|
jpayne@68
|
3005 or png_calloc() to allocate it.
|
|
jpayne@68
|
3006
|
|
jpayne@68
|
3007 If you allocated your row_pointers in a single block, as suggested above in
|
|
jpayne@68
|
3008 the description of the high level read interface, you must not transfer
|
|
jpayne@68
|
3009 responsibility for freeing it to the png_set_rows or png_read_destroy function,
|
|
jpayne@68
|
3010 because they would also try to free the individual row_pointers[i].
|
|
jpayne@68
|
3011
|
|
jpayne@68
|
3012 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
|
|
jpayne@68
|
3013 separately, do not transfer responsibility for freeing text_ptr to libpng,
|
|
jpayne@68
|
3014 because when libpng fills a png_text structure it combines these members with
|
|
jpayne@68
|
3015 the key member, and png_free_data() will free only text_ptr.key. Similarly,
|
|
jpayne@68
|
3016 if you transfer responsibility for free'ing text_ptr from libpng to your
|
|
jpayne@68
|
3017 application, your application must not separately free those members.
|
|
jpayne@68
|
3018
|
|
jpayne@68
|
3019 The png_free_data() function will turn off the "valid" flag for anything
|
|
jpayne@68
|
3020 it frees. If you need to turn the flag off for a chunk that was freed by
|
|
jpayne@68
|
3021 your application instead of by libpng, you can use
|
|
jpayne@68
|
3022
|
|
jpayne@68
|
3023 png_set_invalid(png_ptr, info_ptr, mask);
|
|
jpayne@68
|
3024
|
|
jpayne@68
|
3025 mask - identifies the chunks to be made invalid,
|
|
jpayne@68
|
3026 containing the bitwise OR of one or
|
|
jpayne@68
|
3027 more of
|
|
jpayne@68
|
3028 PNG_INFO_gAMA, PNG_INFO_sBIT,
|
|
jpayne@68
|
3029 PNG_INFO_cHRM, PNG_INFO_PLTE,
|
|
jpayne@68
|
3030 PNG_INFO_tRNS, PNG_INFO_bKGD,
|
|
jpayne@68
|
3031 PNG_INFO_eXIf,
|
|
jpayne@68
|
3032 PNG_INFO_hIST, PNG_INFO_pHYs,
|
|
jpayne@68
|
3033 PNG_INFO_oFFs, PNG_INFO_tIME,
|
|
jpayne@68
|
3034 PNG_INFO_pCAL, PNG_INFO_sRGB,
|
|
jpayne@68
|
3035 PNG_INFO_iCCP, PNG_INFO_sPLT,
|
|
jpayne@68
|
3036 PNG_INFO_sCAL, PNG_INFO_IDAT
|
|
jpayne@68
|
3037
|
|
jpayne@68
|
3038 For a more compact example of reading a PNG image, see the file example.c.
|
|
jpayne@68
|
3039
|
|
jpayne@68
|
3040 .SS Reading PNG files progressively
|
|
jpayne@68
|
3041
|
|
jpayne@68
|
3042 The progressive reader is slightly different from the non-progressive
|
|
jpayne@68
|
3043 reader. Instead of calling png_read_info(), png_read_rows(), and
|
|
jpayne@68
|
3044 png_read_end(), you make one call to png_process_data(), which calls
|
|
jpayne@68
|
3045 callbacks when it has the info, a row, or the end of the image. You
|
|
jpayne@68
|
3046 set up these callbacks with png_set_progressive_read_fn(). You don't
|
|
jpayne@68
|
3047 have to worry about the input/output functions of libpng, as you are
|
|
jpayne@68
|
3048 giving the library the data directly in png_process_data(). I will
|
|
jpayne@68
|
3049 assume that you have read the section on reading PNG files above,
|
|
jpayne@68
|
3050 so I will only highlight the differences (although I will show
|
|
jpayne@68
|
3051 all of the code).
|
|
jpayne@68
|
3052
|
|
jpayne@68
|
3053 png_structp png_ptr;
|
|
jpayne@68
|
3054 png_infop info_ptr;
|
|
jpayne@68
|
3055
|
|
jpayne@68
|
3056 /* An example code fragment of how you would
|
|
jpayne@68
|
3057 initialize the progressive reader in your
|
|
jpayne@68
|
3058 application. */
|
|
jpayne@68
|
3059 int
|
|
jpayne@68
|
3060 initialize_png_reader()
|
|
jpayne@68
|
3061 {
|
|
jpayne@68
|
3062 png_ptr = png_create_read_struct
|
|
jpayne@68
|
3063 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
jpayne@68
|
3064 user_error_fn, user_warning_fn);
|
|
jpayne@68
|
3065
|
|
jpayne@68
|
3066 if (!png_ptr)
|
|
jpayne@68
|
3067 return ERROR;
|
|
jpayne@68
|
3068
|
|
jpayne@68
|
3069 info_ptr = png_create_info_struct(png_ptr);
|
|
jpayne@68
|
3070
|
|
jpayne@68
|
3071 if (!info_ptr)
|
|
jpayne@68
|
3072 {
|
|
jpayne@68
|
3073 png_destroy_read_struct(&png_ptr, NULL, NULL);
|
|
jpayne@68
|
3074 return ERROR;
|
|
jpayne@68
|
3075 }
|
|
jpayne@68
|
3076
|
|
jpayne@68
|
3077 if (setjmp(png_jmpbuf(png_ptr)))
|
|
jpayne@68
|
3078 {
|
|
jpayne@68
|
3079 png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
|
|
jpayne@68
|
3080 return ERROR;
|
|
jpayne@68
|
3081 }
|
|
jpayne@68
|
3082
|
|
jpayne@68
|
3083 /* This one's new. You can provide functions
|
|
jpayne@68
|
3084 to be called when the header info is valid,
|
|
jpayne@68
|
3085 when each row is completed, and when the image
|
|
jpayne@68
|
3086 is finished. If you aren't using all functions,
|
|
jpayne@68
|
3087 you can specify NULL parameters. Even when all
|
|
jpayne@68
|
3088 three functions are NULL, you need to call
|
|
jpayne@68
|
3089 png_set_progressive_read_fn(). You can use
|
|
jpayne@68
|
3090 any struct as the user_ptr (cast to a void pointer
|
|
jpayne@68
|
3091 for the function call), and retrieve the pointer
|
|
jpayne@68
|
3092 from inside the callbacks using the function
|
|
jpayne@68
|
3093
|
|
jpayne@68
|
3094 png_get_progressive_ptr(png_ptr);
|
|
jpayne@68
|
3095
|
|
jpayne@68
|
3096 which will return a void pointer, which you have
|
|
jpayne@68
|
3097 to cast appropriately.
|
|
jpayne@68
|
3098 */
|
|
jpayne@68
|
3099 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
|
|
jpayne@68
|
3100 info_callback, row_callback, end_callback);
|
|
jpayne@68
|
3101
|
|
jpayne@68
|
3102 return 0;
|
|
jpayne@68
|
3103 }
|
|
jpayne@68
|
3104
|
|
jpayne@68
|
3105 /* A code fragment that you call as you receive blocks
|
|
jpayne@68
|
3106 of data */
|
|
jpayne@68
|
3107 int
|
|
jpayne@68
|
3108 process_data(png_bytep buffer, png_uint_32 length)
|
|
jpayne@68
|
3109 {
|
|
jpayne@68
|
3110 if (setjmp(png_jmpbuf(png_ptr)))
|
|
jpayne@68
|
3111 {
|
|
jpayne@68
|
3112 png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
|
|
jpayne@68
|
3113 return ERROR;
|
|
jpayne@68
|
3114 }
|
|
jpayne@68
|
3115
|
|
jpayne@68
|
3116 /* This one's new also. Simply give it a chunk
|
|
jpayne@68
|
3117 of data from the file stream (in order, of
|
|
jpayne@68
|
3118 course). On machines with segmented memory
|
|
jpayne@68
|
3119 models machines, don't give it any more than
|
|
jpayne@68
|
3120 64K. The library seems to run fine with sizes
|
|
jpayne@68
|
3121 of 4K. Although you can give it much less if
|
|
jpayne@68
|
3122 necessary (I assume you can give it chunks of
|
|
jpayne@68
|
3123 1 byte, I haven't tried less than 256 bytes
|
|
jpayne@68
|
3124 yet). When this function returns, you may
|
|
jpayne@68
|
3125 want to display any rows that were generated
|
|
jpayne@68
|
3126 in the row callback if you don't already do
|
|
jpayne@68
|
3127 so there.
|
|
jpayne@68
|
3128 */
|
|
jpayne@68
|
3129 png_process_data(png_ptr, info_ptr, buffer, length);
|
|
jpayne@68
|
3130
|
|
jpayne@68
|
3131 /* At this point you can call png_process_data_skip if
|
|
jpayne@68
|
3132 you want to handle data the library will skip yourself;
|
|
jpayne@68
|
3133 it simply returns the number of bytes to skip (and stops
|
|
jpayne@68
|
3134 libpng skipping that number of bytes on the next
|
|
jpayne@68
|
3135 png_process_data call).
|
|
jpayne@68
|
3136 return 0;
|
|
jpayne@68
|
3137 }
|
|
jpayne@68
|
3138
|
|
jpayne@68
|
3139 /* This function is called (as set by
|
|
jpayne@68
|
3140 png_set_progressive_read_fn() above) when enough data
|
|
jpayne@68
|
3141 has been supplied so all of the header has been
|
|
jpayne@68
|
3142 read.
|
|
jpayne@68
|
3143 */
|
|
jpayne@68
|
3144 void
|
|
jpayne@68
|
3145 info_callback(png_structp png_ptr, png_infop info)
|
|
jpayne@68
|
3146 {
|
|
jpayne@68
|
3147 /* Do any setup here, including setting any of
|
|
jpayne@68
|
3148 the transformations mentioned in the Reading
|
|
jpayne@68
|
3149 PNG files section. For now, you _must_ call
|
|
jpayne@68
|
3150 either png_start_read_image() or
|
|
jpayne@68
|
3151 png_read_update_info() after all the
|
|
jpayne@68
|
3152 transformations are set (even if you don't set
|
|
jpayne@68
|
3153 any). You may start getting rows before
|
|
jpayne@68
|
3154 png_process_data() returns, so this is your
|
|
jpayne@68
|
3155 last chance to prepare for that.
|
|
jpayne@68
|
3156
|
|
jpayne@68
|
3157 This is where you turn on interlace handling,
|
|
jpayne@68
|
3158 assuming you don't want to do it yourself.
|
|
jpayne@68
|
3159
|
|
jpayne@68
|
3160 If you need to you can stop the processing of
|
|
jpayne@68
|
3161 your original input data at this point by calling
|
|
jpayne@68
|
3162 png_process_data_pause. This returns the number
|
|
jpayne@68
|
3163 of unprocessed bytes from the last png_process_data
|
|
jpayne@68
|
3164 call - it is up to you to ensure that the next call
|
|
jpayne@68
|
3165 sees these bytes again. If you don't want to bother
|
|
jpayne@68
|
3166 with this you can get libpng to cache the unread
|
|
jpayne@68
|
3167 bytes by setting the 'save' parameter (see png.h) but
|
|
jpayne@68
|
3168 then libpng will have to copy the data internally.
|
|
jpayne@68
|
3169 */
|
|
jpayne@68
|
3170 }
|
|
jpayne@68
|
3171
|
|
jpayne@68
|
3172 /* This function is called when each row of image
|
|
jpayne@68
|
3173 data is complete */
|
|
jpayne@68
|
3174 void
|
|
jpayne@68
|
3175 row_callback(png_structp png_ptr, png_bytep new_row,
|
|
jpayne@68
|
3176 png_uint_32 row_num, int pass)
|
|
jpayne@68
|
3177 {
|
|
jpayne@68
|
3178 /* If the image is interlaced, and you turned
|
|
jpayne@68
|
3179 on the interlace handler, this function will
|
|
jpayne@68
|
3180 be called for every row in every pass. Some
|
|
jpayne@68
|
3181 of these rows will not be changed from the
|
|
jpayne@68
|
3182 previous pass. When the row is not changed,
|
|
jpayne@68
|
3183 the new_row variable will be NULL. The rows
|
|
jpayne@68
|
3184 and passes are called in order, so you don't
|
|
jpayne@68
|
3185 really need the row_num and pass, but I'm
|
|
jpayne@68
|
3186 supplying them because it may make your life
|
|
jpayne@68
|
3187 easier.
|
|
jpayne@68
|
3188
|
|
jpayne@68
|
3189 If you did not turn on interlace handling then
|
|
jpayne@68
|
3190 the callback is called for each row of each
|
|
jpayne@68
|
3191 sub-image when the image is interlaced. In this
|
|
jpayne@68
|
3192 case 'row_num' is the row in the sub-image, not
|
|
jpayne@68
|
3193 the row in the output image as it is in all other
|
|
jpayne@68
|
3194 cases.
|
|
jpayne@68
|
3195
|
|
jpayne@68
|
3196 For the non-NULL rows of interlaced images when
|
|
jpayne@68
|
3197 you have switched on libpng interlace handling,
|
|
jpayne@68
|
3198 you must call png_progressive_combine_row()
|
|
jpayne@68
|
3199 passing in the row and the old row. You can
|
|
jpayne@68
|
3200 call this function for NULL rows (it will just
|
|
jpayne@68
|
3201 return) and for non-interlaced images (it just
|
|
jpayne@68
|
3202 does the memcpy for you) if it will make the
|
|
jpayne@68
|
3203 code easier. Thus, you can just do this for
|
|
jpayne@68
|
3204 all cases if you switch on interlace handling;
|
|
jpayne@68
|
3205 */
|
|
jpayne@68
|
3206
|
|
jpayne@68
|
3207 png_progressive_combine_row(png_ptr, old_row,
|
|
jpayne@68
|
3208 new_row);
|
|
jpayne@68
|
3209
|
|
jpayne@68
|
3210 /* where old_row is what was displayed
|
|
jpayne@68
|
3211 previously for the row. Note that the first
|
|
jpayne@68
|
3212 pass (pass == 0, really) will completely cover
|
|
jpayne@68
|
3213 the old row, so the rows do not have to be
|
|
jpayne@68
|
3214 initialized. After the first pass (and only
|
|
jpayne@68
|
3215 for interlaced images), you will have to pass
|
|
jpayne@68
|
3216 the current row, and the function will combine
|
|
jpayne@68
|
3217 the old row and the new row.
|
|
jpayne@68
|
3218
|
|
jpayne@68
|
3219 You can also call png_process_data_pause in this
|
|
jpayne@68
|
3220 callback - see above.
|
|
jpayne@68
|
3221 */
|
|
jpayne@68
|
3222 }
|
|
jpayne@68
|
3223
|
|
jpayne@68
|
3224 void
|
|
jpayne@68
|
3225 end_callback(png_structp png_ptr, png_infop info)
|
|
jpayne@68
|
3226 {
|
|
jpayne@68
|
3227 /* This function is called after the whole image
|
|
jpayne@68
|
3228 has been read, including any chunks after the
|
|
jpayne@68
|
3229 image (up to and including the IEND). You
|
|
jpayne@68
|
3230 will usually have the same info chunk as you
|
|
jpayne@68
|
3231 had in the header, although some data may have
|
|
jpayne@68
|
3232 been added to the comments and time fields.
|
|
jpayne@68
|
3233
|
|
jpayne@68
|
3234 Most people won't do much here, perhaps setting
|
|
jpayne@68
|
3235 a flag that marks the image as finished.
|
|
jpayne@68
|
3236 */
|
|
jpayne@68
|
3237 }
|
|
jpayne@68
|
3238
|
|
jpayne@68
|
3239
|
|
jpayne@68
|
3240
|
|
jpayne@68
|
3241 .SH IV. Writing
|
|
jpayne@68
|
3242
|
|
jpayne@68
|
3243 Much of this is very similar to reading. However, everything of
|
|
jpayne@68
|
3244 importance is repeated here, so you won't have to constantly look
|
|
jpayne@68
|
3245 back up in the reading section to understand writing.
|
|
jpayne@68
|
3246
|
|
jpayne@68
|
3247 .SS Setup
|
|
jpayne@68
|
3248
|
|
jpayne@68
|
3249 You will want to do the I/O initialization before you get into libpng,
|
|
jpayne@68
|
3250 so if it doesn't work, you don't have anything to undo. If you are not
|
|
jpayne@68
|
3251 using the standard I/O functions, you will need to replace them with
|
|
jpayne@68
|
3252 custom writing functions. See the discussion under Customizing libpng.
|
|
jpayne@68
|
3253
|
|
jpayne@68
|
3254 FILE *fp = fopen(file_name, "wb");
|
|
jpayne@68
|
3255
|
|
jpayne@68
|
3256 if (!fp)
|
|
jpayne@68
|
3257 return ERROR;
|
|
jpayne@68
|
3258
|
|
jpayne@68
|
3259 Next, png_struct and png_info need to be allocated and initialized.
|
|
jpayne@68
|
3260 As these can be both relatively large, you may not want to store these
|
|
jpayne@68
|
3261 on the stack, unless you have stack space to spare. Of course, you
|
|
jpayne@68
|
3262 will want to check if they return NULL. If you are also reading,
|
|
jpayne@68
|
3263 you won't want to name your read structure and your write structure
|
|
jpayne@68
|
3264 both "png_ptr"; you can call them anything you like, such as
|
|
jpayne@68
|
3265 "read_ptr" and "write_ptr". Look at pngtest.c, for example.
|
|
jpayne@68
|
3266
|
|
jpayne@68
|
3267 png_structp png_ptr = png_create_write_struct
|
|
jpayne@68
|
3268 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
jpayne@68
|
3269 user_error_fn, user_warning_fn);
|
|
jpayne@68
|
3270
|
|
jpayne@68
|
3271 if (!png_ptr)
|
|
jpayne@68
|
3272 return ERROR;
|
|
jpayne@68
|
3273
|
|
jpayne@68
|
3274 png_infop info_ptr = png_create_info_struct(png_ptr);
|
|
jpayne@68
|
3275 if (!info_ptr)
|
|
jpayne@68
|
3276 {
|
|
jpayne@68
|
3277 png_destroy_write_struct(&png_ptr, NULL);
|
|
jpayne@68
|
3278 return ERROR;
|
|
jpayne@68
|
3279 }
|
|
jpayne@68
|
3280
|
|
jpayne@68
|
3281 If you want to use your own memory allocation routines,
|
|
jpayne@68
|
3282 define PNG_USER_MEM_SUPPORTED and use
|
|
jpayne@68
|
3283 png_create_write_struct_2() instead of png_create_write_struct():
|
|
jpayne@68
|
3284
|
|
jpayne@68
|
3285 png_structp png_ptr = png_create_write_struct_2
|
|
jpayne@68
|
3286 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
jpayne@68
|
3287 user_error_fn, user_warning_fn, (png_voidp)
|
|
jpayne@68
|
3288 user_mem_ptr, user_malloc_fn, user_free_fn);
|
|
jpayne@68
|
3289
|
|
jpayne@68
|
3290 After you have these structures, you will need to set up the
|
|
jpayne@68
|
3291 error handling. When libpng encounters an error, it expects to
|
|
jpayne@68
|
3292 longjmp() back to your routine. Therefore, you will need to call
|
|
jpayne@68
|
3293 setjmp() and pass the png_jmpbuf(png_ptr). If you
|
|
jpayne@68
|
3294 write the file from different routines, you will need to update
|
|
jpayne@68
|
3295 the png_jmpbuf(png_ptr) every time you enter a new routine that will
|
|
jpayne@68
|
3296 call a png_*() function. See your documentation of setjmp/longjmp
|
|
jpayne@68
|
3297 for your compiler for more information on setjmp/longjmp. See
|
|
jpayne@68
|
3298 the discussion on libpng error handling in the Customizing Libpng
|
|
jpayne@68
|
3299 section below for more information on the libpng error handling.
|
|
jpayne@68
|
3300
|
|
jpayne@68
|
3301 if (setjmp(png_jmpbuf(png_ptr)))
|
|
jpayne@68
|
3302 {
|
|
jpayne@68
|
3303 png_destroy_write_struct(&png_ptr, &info_ptr);
|
|
jpayne@68
|
3304 fclose(fp);
|
|
jpayne@68
|
3305 return ERROR;
|
|
jpayne@68
|
3306 }
|
|
jpayne@68
|
3307 ...
|
|
jpayne@68
|
3308 return;
|
|
jpayne@68
|
3309
|
|
jpayne@68
|
3310 If you would rather avoid the complexity of setjmp/longjmp issues,
|
|
jpayne@68
|
3311 you can compile libpng with PNG_NO_SETJMP, in which case
|
|
jpayne@68
|
3312 errors will result in a call to PNG_ABORT() which defaults to abort().
|
|
jpayne@68
|
3313
|
|
jpayne@68
|
3314 You can #define PNG_ABORT() to a function that does something
|
|
jpayne@68
|
3315 more useful than abort(), as long as your function does not
|
|
jpayne@68
|
3316 return.
|
|
jpayne@68
|
3317
|
|
jpayne@68
|
3318 Checking for invalid palette index on write was added at libpng
|
|
jpayne@68
|
3319 1.5.10. If a pixel contains an invalid (out-of-range) index libpng issues
|
|
jpayne@68
|
3320 a benign error. This is enabled by default because this condition is an
|
|
jpayne@68
|
3321 error according to the PNG specification, Clause 11.3.2, but the error can
|
|
jpayne@68
|
3322 be ignored in each png_ptr with
|
|
jpayne@68
|
3323
|
|
jpayne@68
|
3324 png_set_check_for_invalid_index(png_ptr, 0);
|
|
jpayne@68
|
3325
|
|
jpayne@68
|
3326 If the error is ignored, or if png_benign_error() treats it as a warning,
|
|
jpayne@68
|
3327 any invalid pixels are written as-is by the encoder, resulting in an
|
|
jpayne@68
|
3328 invalid PNG datastream as output. In this case the application is
|
|
jpayne@68
|
3329 responsible for ensuring that the pixel indexes are in range when it writes
|
|
jpayne@68
|
3330 a PLTE chunk with fewer entries than the bit depth would allow.
|
|
jpayne@68
|
3331
|
|
jpayne@68
|
3332 Now you need to set up the output code. The default for libpng is to
|
|
jpayne@68
|
3333 use the C function fwrite(). If you use this, you will need to pass a
|
|
jpayne@68
|
3334 valid FILE * in the function png_init_io(). Be sure that the file is
|
|
jpayne@68
|
3335 opened in binary mode. Again, if you wish to handle writing data in
|
|
jpayne@68
|
3336 another way, see the discussion on libpng I/O handling in the Customizing
|
|
jpayne@68
|
3337 Libpng section below.
|
|
jpayne@68
|
3338
|
|
jpayne@68
|
3339 png_init_io(png_ptr, fp);
|
|
jpayne@68
|
3340
|
|
jpayne@68
|
3341 If you are embedding your PNG into a datastream such as MNG, and don't
|
|
jpayne@68
|
3342 want libpng to write the 8-byte signature, or if you have already
|
|
jpayne@68
|
3343 written the signature in your application, use
|
|
jpayne@68
|
3344
|
|
jpayne@68
|
3345 png_set_sig_bytes(png_ptr, 8);
|
|
jpayne@68
|
3346
|
|
jpayne@68
|
3347 to inform libpng that it should not write a signature.
|
|
jpayne@68
|
3348
|
|
jpayne@68
|
3349 .SS Write callbacks
|
|
jpayne@68
|
3350
|
|
jpayne@68
|
3351 At this point, you can set up a callback function that will be
|
|
jpayne@68
|
3352 called after each row has been written, which you can use to control
|
|
jpayne@68
|
3353 a progress meter or the like. It's demonstrated in pngtest.c.
|
|
jpayne@68
|
3354 You must supply a function
|
|
jpayne@68
|
3355
|
|
jpayne@68
|
3356 void write_row_callback(png_structp png_ptr, png_uint_32 row,
|
|
jpayne@68
|
3357 int pass)
|
|
jpayne@68
|
3358 {
|
|
jpayne@68
|
3359 /* put your code here */
|
|
jpayne@68
|
3360 }
|
|
jpayne@68
|
3361
|
|
jpayne@68
|
3362 (You can give it another name that you like instead of "write_row_callback")
|
|
jpayne@68
|
3363
|
|
jpayne@68
|
3364 To inform libpng about your function, use
|
|
jpayne@68
|
3365
|
|
jpayne@68
|
3366 png_set_write_status_fn(png_ptr, write_row_callback);
|
|
jpayne@68
|
3367
|
|
jpayne@68
|
3368 When this function is called the row has already been completely processed and
|
|
jpayne@68
|
3369 it has also been written out. The 'row' and 'pass' refer to the next row to be
|
|
jpayne@68
|
3370 handled. For the
|
|
jpayne@68
|
3371 non-interlaced case the row that was just handled is simply one less than the
|
|
jpayne@68
|
3372 passed in row number, and pass will always be 0. For the interlaced case the
|
|
jpayne@68
|
3373 same applies unless the row value is 0, in which case the row just handled was
|
|
jpayne@68
|
3374 the last one from one of the preceding passes. Because interlacing may skip a
|
|
jpayne@68
|
3375 pass you cannot be sure that the preceding pass is just 'pass\-1', if you really
|
|
jpayne@68
|
3376 need to know what the last pass is record (row,pass) from the callback and use
|
|
jpayne@68
|
3377 the last recorded value each time.
|
|
jpayne@68
|
3378
|
|
jpayne@68
|
3379 As with the user transform you can find the output row using the
|
|
jpayne@68
|
3380 PNG_ROW_FROM_PASS_ROW macro.
|
|
jpayne@68
|
3381
|
|
jpayne@68
|
3382 You now have the option of modifying how the compression library will
|
|
jpayne@68
|
3383 run. The following functions are mainly for testing, but may be useful
|
|
jpayne@68
|
3384 in some cases, like if you need to write PNG files extremely fast and
|
|
jpayne@68
|
3385 are willing to give up some compression, or if you want to get the
|
|
jpayne@68
|
3386 maximum possible compression at the expense of slower writing. If you
|
|
jpayne@68
|
3387 have no special needs in this area, let the library do what it wants by
|
|
jpayne@68
|
3388 not calling this function at all, as it has been tuned to deliver a good
|
|
jpayne@68
|
3389 speed/compression ratio. The second parameter to png_set_filter() is
|
|
jpayne@68
|
3390 the filter method, for which the only valid values are 0 (as of the
|
|
jpayne@68
|
3391 July 1999 PNG specification, version 1.2) or 64 (if you are writing
|
|
jpayne@68
|
3392 a PNG datastream that is to be embedded in a MNG datastream). The third
|
|
jpayne@68
|
3393 parameter is a flag that indicates which filter type(s) are to be tested
|
|
jpayne@68
|
3394 for each scanline. See the PNG specification for details on the specific
|
|
jpayne@68
|
3395 filter types.
|
|
jpayne@68
|
3396
|
|
jpayne@68
|
3397
|
|
jpayne@68
|
3398 /* turn on or off filtering, and/or choose
|
|
jpayne@68
|
3399 specific filters. You can use either a single
|
|
jpayne@68
|
3400 PNG_FILTER_VALUE_NAME or the bitwise OR of one
|
|
jpayne@68
|
3401 or more PNG_FILTER_NAME masks.
|
|
jpayne@68
|
3402 */
|
|
jpayne@68
|
3403 png_set_filter(png_ptr, 0,
|
|
jpayne@68
|
3404 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
|
|
jpayne@68
|
3405 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
|
|
jpayne@68
|
3406 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
|
|
jpayne@68
|
3407 PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
|
|
jpayne@68
|
3408 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
|
|
jpayne@68
|
3409 PNG_ALL_FILTERS | PNG_FAST_FILTERS);
|
|
jpayne@68
|
3410
|
|
jpayne@68
|
3411 If an application wants to start and stop using particular filters during
|
|
jpayne@68
|
3412 compression, it should start out with all of the filters (to ensure that
|
|
jpayne@68
|
3413 the previous row of pixels will be stored in case it's needed later),
|
|
jpayne@68
|
3414 and then add and remove them after the start of compression.
|
|
jpayne@68
|
3415
|
|
jpayne@68
|
3416 If you are writing a PNG datastream that is to be embedded in a MNG
|
|
jpayne@68
|
3417 datastream, the second parameter can be either 0 or 64.
|
|
jpayne@68
|
3418
|
|
jpayne@68
|
3419 The png_set_compression_*() functions interface to the zlib compression
|
|
jpayne@68
|
3420 library, and should mostly be ignored unless you really know what you are
|
|
jpayne@68
|
3421 doing. The only generally useful call is png_set_compression_level()
|
|
jpayne@68
|
3422 which changes how much time zlib spends on trying to compress the image
|
|
jpayne@68
|
3423 data. See the Compression Library (zlib.h and algorithm.txt, distributed
|
|
jpayne@68
|
3424 with zlib) for details on the compression levels.
|
|
jpayne@68
|
3425
|
|
jpayne@68
|
3426 #include zlib.h
|
|
jpayne@68
|
3427
|
|
jpayne@68
|
3428 /* Set the zlib compression level */
|
|
jpayne@68
|
3429 png_set_compression_level(png_ptr,
|
|
jpayne@68
|
3430 Z_BEST_COMPRESSION);
|
|
jpayne@68
|
3431
|
|
jpayne@68
|
3432 /* Set other zlib parameters for compressing IDAT */
|
|
jpayne@68
|
3433 png_set_compression_mem_level(png_ptr, 8);
|
|
jpayne@68
|
3434 png_set_compression_strategy(png_ptr,
|
|
jpayne@68
|
3435 Z_DEFAULT_STRATEGY);
|
|
jpayne@68
|
3436 png_set_compression_window_bits(png_ptr, 15);
|
|
jpayne@68
|
3437 png_set_compression_method(png_ptr, 8);
|
|
jpayne@68
|
3438 png_set_compression_buffer_size(png_ptr, 8192)
|
|
jpayne@68
|
3439
|
|
jpayne@68
|
3440 /* Set zlib parameters for text compression
|
|
jpayne@68
|
3441 * If you don't call these, the parameters
|
|
jpayne@68
|
3442 * fall back on those defined for IDAT chunks
|
|
jpayne@68
|
3443 */
|
|
jpayne@68
|
3444 png_set_text_compression_mem_level(png_ptr, 8);
|
|
jpayne@68
|
3445 png_set_text_compression_strategy(png_ptr,
|
|
jpayne@68
|
3446 Z_DEFAULT_STRATEGY);
|
|
jpayne@68
|
3447 png_set_text_compression_window_bits(png_ptr, 15);
|
|
jpayne@68
|
3448 png_set_text_compression_method(png_ptr, 8);
|
|
jpayne@68
|
3449
|
|
jpayne@68
|
3450 .SS Setting the contents of info for output
|
|
jpayne@68
|
3451
|
|
jpayne@68
|
3452 You now need to fill in the png_info structure with all the data you
|
|
jpayne@68
|
3453 wish to write before the actual image. Note that the only thing you
|
|
jpayne@68
|
3454 are allowed to write after the image is the text chunks and the time
|
|
jpayne@68
|
3455 chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
|
|
jpayne@68
|
3456 the latest PNG specification for more information on that. If you
|
|
jpayne@68
|
3457 wish to write them before the image, fill them in now, and flag that
|
|
jpayne@68
|
3458 data as being valid. If you want to wait until after the data, don't
|
|
jpayne@68
|
3459 fill them until png_write_end(). For all the fields in png_info and
|
|
jpayne@68
|
3460 their data types, see png.h. For explanations of what the fields
|
|
jpayne@68
|
3461 contain, see the PNG specification.
|
|
jpayne@68
|
3462
|
|
jpayne@68
|
3463 Some of the more important parts of the png_info are:
|
|
jpayne@68
|
3464
|
|
jpayne@68
|
3465 png_set_IHDR(png_ptr, info_ptr, width, height,
|
|
jpayne@68
|
3466 bit_depth, color_type, interlace_type,
|
|
jpayne@68
|
3467 compression_type, filter_method)
|
|
jpayne@68
|
3468
|
|
jpayne@68
|
3469 width - holds the width of the image
|
|
jpayne@68
|
3470 in pixels (up to 2^31).
|
|
jpayne@68
|
3471
|
|
jpayne@68
|
3472 height - holds the height of the image
|
|
jpayne@68
|
3473 in pixels (up to 2^31).
|
|
jpayne@68
|
3474
|
|
jpayne@68
|
3475 bit_depth - holds the bit depth of one of the
|
|
jpayne@68
|
3476 image channels.
|
|
jpayne@68
|
3477 (valid values are 1, 2, 4, 8, 16
|
|
jpayne@68
|
3478 and depend also on the
|
|
jpayne@68
|
3479 color_type. See also significant
|
|
jpayne@68
|
3480 bits (sBIT) below).
|
|
jpayne@68
|
3481
|
|
jpayne@68
|
3482 color_type - describes which color/alpha
|
|
jpayne@68
|
3483 channels are present.
|
|
jpayne@68
|
3484 PNG_COLOR_TYPE_GRAY
|
|
jpayne@68
|
3485 (bit depths 1, 2, 4, 8, 16)
|
|
jpayne@68
|
3486 PNG_COLOR_TYPE_GRAY_ALPHA
|
|
jpayne@68
|
3487 (bit depths 8, 16)
|
|
jpayne@68
|
3488 PNG_COLOR_TYPE_PALETTE
|
|
jpayne@68
|
3489 (bit depths 1, 2, 4, 8)
|
|
jpayne@68
|
3490 PNG_COLOR_TYPE_RGB
|
|
jpayne@68
|
3491 (bit_depths 8, 16)
|
|
jpayne@68
|
3492 PNG_COLOR_TYPE_RGB_ALPHA
|
|
jpayne@68
|
3493 (bit_depths 8, 16)
|
|
jpayne@68
|
3494
|
|
jpayne@68
|
3495 PNG_COLOR_MASK_PALETTE
|
|
jpayne@68
|
3496 PNG_COLOR_MASK_COLOR
|
|
jpayne@68
|
3497 PNG_COLOR_MASK_ALPHA
|
|
jpayne@68
|
3498
|
|
jpayne@68
|
3499 interlace_type - PNG_INTERLACE_NONE or
|
|
jpayne@68
|
3500 PNG_INTERLACE_ADAM7
|
|
jpayne@68
|
3501
|
|
jpayne@68
|
3502 compression_type - (must be
|
|
jpayne@68
|
3503 PNG_COMPRESSION_TYPE_DEFAULT)
|
|
jpayne@68
|
3504
|
|
jpayne@68
|
3505 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
|
|
jpayne@68
|
3506 or, if you are writing a PNG to
|
|
jpayne@68
|
3507 be embedded in a MNG datastream,
|
|
jpayne@68
|
3508 can also be
|
|
jpayne@68
|
3509 PNG_INTRAPIXEL_DIFFERENCING)
|
|
jpayne@68
|
3510
|
|
jpayne@68
|
3511 If you call png_set_IHDR(), the call must appear before any of the
|
|
jpayne@68
|
3512 other png_set_*() functions, because they might require access to some of
|
|
jpayne@68
|
3513 the IHDR settings. The remaining png_set_*() functions can be called
|
|
jpayne@68
|
3514 in any order.
|
|
jpayne@68
|
3515
|
|
jpayne@68
|
3516 If you wish, you can reset the compression_type, interlace_type, or
|
|
jpayne@68
|
3517 filter_method later by calling png_set_IHDR() again; if you do this, the
|
|
jpayne@68
|
3518 width, height, bit_depth, and color_type must be the same in each call.
|
|
jpayne@68
|
3519
|
|
jpayne@68
|
3520 png_set_PLTE(png_ptr, info_ptr, palette,
|
|
jpayne@68
|
3521 num_palette);
|
|
jpayne@68
|
3522
|
|
jpayne@68
|
3523 palette - the palette for the file
|
|
jpayne@68
|
3524 (array of png_color)
|
|
jpayne@68
|
3525 num_palette - number of entries in the palette
|
|
jpayne@68
|
3526
|
|
jpayne@68
|
3527
|
|
jpayne@68
|
3528 png_set_gAMA(png_ptr, info_ptr, file_gamma);
|
|
jpayne@68
|
3529 png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma);
|
|
jpayne@68
|
3530
|
|
jpayne@68
|
3531 file_gamma - the gamma at which the image was
|
|
jpayne@68
|
3532 created (PNG_INFO_gAMA)
|
|
jpayne@68
|
3533
|
|
jpayne@68
|
3534 int_file_gamma - 100,000 times the gamma at which
|
|
jpayne@68
|
3535 the image was created
|
|
jpayne@68
|
3536
|
|
jpayne@68
|
3537 png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y,
|
|
jpayne@68
|
3538 green_x, green_y, blue_x, blue_y)
|
|
jpayne@68
|
3539 png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X,
|
|
jpayne@68
|
3540 green_Y, green_Z, blue_X, blue_Y, blue_Z)
|
|
jpayne@68
|
3541 png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y,
|
|
jpayne@68
|
3542 int_red_x, int_red_y, int_green_x, int_green_y,
|
|
jpayne@68
|
3543 int_blue_x, int_blue_y)
|
|
jpayne@68
|
3544 png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y,
|
|
jpayne@68
|
3545 int_red_Z, int_green_X, int_green_Y, int_green_Z,
|
|
jpayne@68
|
3546 int_blue_X, int_blue_Y, int_blue_Z)
|
|
jpayne@68
|
3547
|
|
jpayne@68
|
3548 {white,red,green,blue}_{x,y}
|
|
jpayne@68
|
3549 A color space encoding specified using the chromaticities
|
|
jpayne@68
|
3550 of the end points and the white point.
|
|
jpayne@68
|
3551
|
|
jpayne@68
|
3552 {red,green,blue}_{X,Y,Z}
|
|
jpayne@68
|
3553 A color space encoding specified using the encoding end
|
|
jpayne@68
|
3554 points - the CIE tristimulus specification of the intended
|
|
jpayne@68
|
3555 color of the red, green and blue channels in the PNG RGB
|
|
jpayne@68
|
3556 data. The white point is simply the sum of the three end
|
|
jpayne@68
|
3557 points.
|
|
jpayne@68
|
3558
|
|
jpayne@68
|
3559 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
|
|
jpayne@68
|
3560
|
|
jpayne@68
|
3561 srgb_intent - the rendering intent
|
|
jpayne@68
|
3562 (PNG_INFO_sRGB) The presence of
|
|
jpayne@68
|
3563 the sRGB chunk means that the pixel
|
|
jpayne@68
|
3564 data is in the sRGB color space.
|
|
jpayne@68
|
3565 This chunk also implies specific
|
|
jpayne@68
|
3566 values of gAMA and cHRM. Rendering
|
|
jpayne@68
|
3567 intent is the CSS-1 property that
|
|
jpayne@68
|
3568 has been defined by the International
|
|
jpayne@68
|
3569 Color Consortium
|
|
jpayne@68
|
3570 (http://www.color.org).
|
|
jpayne@68
|
3571 It can be one of
|
|
jpayne@68
|
3572 PNG_sRGB_INTENT_SATURATION,
|
|
jpayne@68
|
3573 PNG_sRGB_INTENT_PERCEPTUAL,
|
|
jpayne@68
|
3574 PNG_sRGB_INTENT_ABSOLUTE, or
|
|
jpayne@68
|
3575 PNG_sRGB_INTENT_RELATIVE.
|
|
jpayne@68
|
3576
|
|
jpayne@68
|
3577
|
|
jpayne@68
|
3578 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
|
|
jpayne@68
|
3579 srgb_intent);
|
|
jpayne@68
|
3580
|
|
jpayne@68
|
3581 srgb_intent - the rendering intent
|
|
jpayne@68
|
3582 (PNG_INFO_sRGB) The presence of the
|
|
jpayne@68
|
3583 sRGB chunk means that the pixel
|
|
jpayne@68
|
3584 data is in the sRGB color space.
|
|
jpayne@68
|
3585 This function also causes gAMA and
|
|
jpayne@68
|
3586 cHRM chunks with the specific values
|
|
jpayne@68
|
3587 that are consistent with sRGB to be
|
|
jpayne@68
|
3588 written.
|
|
jpayne@68
|
3589
|
|
jpayne@68
|
3590 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
|
|
jpayne@68
|
3591 profile, proflen);
|
|
jpayne@68
|
3592
|
|
jpayne@68
|
3593 name - The profile name.
|
|
jpayne@68
|
3594
|
|
jpayne@68
|
3595 compression_type - The compression type; always
|
|
jpayne@68
|
3596 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
|
|
jpayne@68
|
3597 You may give NULL to this argument to
|
|
jpayne@68
|
3598 ignore it.
|
|
jpayne@68
|
3599
|
|
jpayne@68
|
3600 profile - International Color Consortium color
|
|
jpayne@68
|
3601 profile data. May contain NULs.
|
|
jpayne@68
|
3602
|
|
jpayne@68
|
3603 proflen - length of profile data in bytes.
|
|
jpayne@68
|
3604
|
|
jpayne@68
|
3605 png_set_sBIT(png_ptr, info_ptr, sig_bit);
|
|
jpayne@68
|
3606
|
|
jpayne@68
|
3607 sig_bit - the number of significant bits for
|
|
jpayne@68
|
3608 (PNG_INFO_sBIT) each of the gray, red,
|
|
jpayne@68
|
3609 green, and blue channels, whichever are
|
|
jpayne@68
|
3610 appropriate for the given color type
|
|
jpayne@68
|
3611 (png_color_16)
|
|
jpayne@68
|
3612
|
|
jpayne@68
|
3613 png_set_tRNS(png_ptr, info_ptr, trans_alpha,
|
|
jpayne@68
|
3614 num_trans, trans_color);
|
|
jpayne@68
|
3615
|
|
jpayne@68
|
3616 trans_alpha - array of alpha (transparency)
|
|
jpayne@68
|
3617 entries for palette (PNG_INFO_tRNS)
|
|
jpayne@68
|
3618
|
|
jpayne@68
|
3619 num_trans - number of transparent entries
|
|
jpayne@68
|
3620 (PNG_INFO_tRNS)
|
|
jpayne@68
|
3621
|
|
jpayne@68
|
3622 trans_color - graylevel or color sample values
|
|
jpayne@68
|
3623 (in order red, green, blue) of the
|
|
jpayne@68
|
3624 single transparent color for
|
|
jpayne@68
|
3625 non-paletted images (PNG_INFO_tRNS)
|
|
jpayne@68
|
3626
|
|
jpayne@68
|
3627 png_set_eXIf_1(png_ptr, info_ptr, num_exif, exif);
|
|
jpayne@68
|
3628
|
|
jpayne@68
|
3629 exif - Exif profile (array of png_byte)
|
|
jpayne@68
|
3630 (PNG_INFO_eXIf)
|
|
jpayne@68
|
3631
|
|
jpayne@68
|
3632 png_set_hIST(png_ptr, info_ptr, hist);
|
|
jpayne@68
|
3633
|
|
jpayne@68
|
3634 hist - histogram of palette (array of
|
|
jpayne@68
|
3635 png_uint_16) (PNG_INFO_hIST)
|
|
jpayne@68
|
3636
|
|
jpayne@68
|
3637 png_set_tIME(png_ptr, info_ptr, mod_time);
|
|
jpayne@68
|
3638
|
|
jpayne@68
|
3639 mod_time - time image was last modified
|
|
jpayne@68
|
3640 (PNG_INFO_tIME)
|
|
jpayne@68
|
3641
|
|
jpayne@68
|
3642 png_set_bKGD(png_ptr, info_ptr, background);
|
|
jpayne@68
|
3643
|
|
jpayne@68
|
3644 background - background color (of type
|
|
jpayne@68
|
3645 png_color_16p) (PNG_INFO_bKGD)
|
|
jpayne@68
|
3646
|
|
jpayne@68
|
3647 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
|
|
jpayne@68
|
3648
|
|
jpayne@68
|
3649 text_ptr - array of png_text holding image
|
|
jpayne@68
|
3650 comments
|
|
jpayne@68
|
3651
|
|
jpayne@68
|
3652 text_ptr[i].compression - type of compression used
|
|
jpayne@68
|
3653 on "text" PNG_TEXT_COMPRESSION_NONE
|
|
jpayne@68
|
3654 PNG_TEXT_COMPRESSION_zTXt
|
|
jpayne@68
|
3655 PNG_ITXT_COMPRESSION_NONE
|
|
jpayne@68
|
3656 PNG_ITXT_COMPRESSION_zTXt
|
|
jpayne@68
|
3657 text_ptr[i].key - keyword for comment. Must contain
|
|
jpayne@68
|
3658 1-79 characters.
|
|
jpayne@68
|
3659 text_ptr[i].text - text comments for current
|
|
jpayne@68
|
3660 keyword. Can be NULL or empty.
|
|
jpayne@68
|
3661 text_ptr[i].text_length - length of text string,
|
|
jpayne@68
|
3662 after decompression, 0 for iTXt
|
|
jpayne@68
|
3663 text_ptr[i].itxt_length - length of itxt string,
|
|
jpayne@68
|
3664 after decompression, 0 for tEXt/zTXt
|
|
jpayne@68
|
3665 text_ptr[i].lang - language of comment (NULL or
|
|
jpayne@68
|
3666 empty for unknown).
|
|
jpayne@68
|
3667 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
|
|
jpayne@68
|
3668 or empty for unknown).
|
|
jpayne@68
|
3669
|
|
jpayne@68
|
3670 Note that the itxt_length, lang, and lang_key
|
|
jpayne@68
|
3671 members of the text_ptr structure only exist when the
|
|
jpayne@68
|
3672 library is built with iTXt chunk support. Prior to
|
|
jpayne@68
|
3673 libpng-1.4.0 the library was built by default without
|
|
jpayne@68
|
3674 iTXt support. Also note that when iTXt is supported,
|
|
jpayne@68
|
3675 they contain NULL pointers when the "compression"
|
|
jpayne@68
|
3676 field contains PNG_TEXT_COMPRESSION_NONE or
|
|
jpayne@68
|
3677 PNG_TEXT_COMPRESSION_zTXt.
|
|
jpayne@68
|
3678
|
|
jpayne@68
|
3679 num_text - number of comments
|
|
jpayne@68
|
3680
|
|
jpayne@68
|
3681 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
|
|
jpayne@68
|
3682 num_spalettes);
|
|
jpayne@68
|
3683
|
|
jpayne@68
|
3684 palette_ptr - array of png_sPLT_struct structures
|
|
jpayne@68
|
3685 to be added to the list of palettes
|
|
jpayne@68
|
3686 in the info structure.
|
|
jpayne@68
|
3687 num_spalettes - number of palette structures to be
|
|
jpayne@68
|
3688 added.
|
|
jpayne@68
|
3689
|
|
jpayne@68
|
3690 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
|
|
jpayne@68
|
3691 unit_type);
|
|
jpayne@68
|
3692
|
|
jpayne@68
|
3693 offset_x - positive offset from the left
|
|
jpayne@68
|
3694 edge of the screen
|
|
jpayne@68
|
3695
|
|
jpayne@68
|
3696 offset_y - positive offset from the top
|
|
jpayne@68
|
3697 edge of the screen
|
|
jpayne@68
|
3698
|
|
jpayne@68
|
3699 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
|
|
jpayne@68
|
3700
|
|
jpayne@68
|
3701 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
|
|
jpayne@68
|
3702 unit_type);
|
|
jpayne@68
|
3703
|
|
jpayne@68
|
3704 res_x - pixels/unit physical resolution
|
|
jpayne@68
|
3705 in x direction
|
|
jpayne@68
|
3706
|
|
jpayne@68
|
3707 res_y - pixels/unit physical resolution
|
|
jpayne@68
|
3708 in y direction
|
|
jpayne@68
|
3709
|
|
jpayne@68
|
3710 unit_type - PNG_RESOLUTION_UNKNOWN,
|
|
jpayne@68
|
3711 PNG_RESOLUTION_METER
|
|
jpayne@68
|
3712
|
|
jpayne@68
|
3713 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
|
|
jpayne@68
|
3714
|
|
jpayne@68
|
3715 unit - physical scale units (an integer)
|
|
jpayne@68
|
3716
|
|
jpayne@68
|
3717 width - width of a pixel in physical scale units
|
|
jpayne@68
|
3718
|
|
jpayne@68
|
3719 height - height of a pixel in physical scale units
|
|
jpayne@68
|
3720 (width and height are doubles)
|
|
jpayne@68
|
3721
|
|
jpayne@68
|
3722 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
|
|
jpayne@68
|
3723
|
|
jpayne@68
|
3724 unit - physical scale units (an integer)
|
|
jpayne@68
|
3725
|
|
jpayne@68
|
3726 width - width of a pixel in physical scale units
|
|
jpayne@68
|
3727 expressed as a string
|
|
jpayne@68
|
3728
|
|
jpayne@68
|
3729 height - height of a pixel in physical scale units
|
|
jpayne@68
|
3730 (width and height are strings like "2.54")
|
|
jpayne@68
|
3731
|
|
jpayne@68
|
3732 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
|
|
jpayne@68
|
3733 num_unknowns)
|
|
jpayne@68
|
3734
|
|
jpayne@68
|
3735 unknowns - array of png_unknown_chunk
|
|
jpayne@68
|
3736 structures holding unknown chunks
|
|
jpayne@68
|
3737 unknowns[i].name - name of unknown chunk
|
|
jpayne@68
|
3738 unknowns[i].data - data of unknown chunk
|
|
jpayne@68
|
3739 unknowns[i].size - size of unknown chunk's data
|
|
jpayne@68
|
3740 unknowns[i].location - position to write chunk in file
|
|
jpayne@68
|
3741 0: do not write chunk
|
|
jpayne@68
|
3742 PNG_HAVE_IHDR: before PLTE
|
|
jpayne@68
|
3743 PNG_HAVE_PLTE: before IDAT
|
|
jpayne@68
|
3744 PNG_AFTER_IDAT: after IDAT
|
|
jpayne@68
|
3745
|
|
jpayne@68
|
3746 The "location" member is set automatically according to
|
|
jpayne@68
|
3747 what part of the output file has already been written.
|
|
jpayne@68
|
3748 You can change its value after calling png_set_unknown_chunks()
|
|
jpayne@68
|
3749 as demonstrated in pngtest.c. Within each of the "locations",
|
|
jpayne@68
|
3750 the chunks are sequenced according to their position in the
|
|
jpayne@68
|
3751 structure (that is, the value of "i", which is the order in which
|
|
jpayne@68
|
3752 the chunk was either read from the input file or defined with
|
|
jpayne@68
|
3753 png_set_unknown_chunks).
|
|
jpayne@68
|
3754
|
|
jpayne@68
|
3755 A quick word about text and num_text. text is an array of png_text
|
|
jpayne@68
|
3756 structures. num_text is the number of valid structures in the array.
|
|
jpayne@68
|
3757 Each png_text structure holds a language code, a keyword, a text value,
|
|
jpayne@68
|
3758 and a compression type.
|
|
jpayne@68
|
3759
|
|
jpayne@68
|
3760 The compression types have the same valid numbers as the compression
|
|
jpayne@68
|
3761 types of the image data. Currently, the only valid number is zero.
|
|
jpayne@68
|
3762 However, you can store text either compressed or uncompressed, unlike
|
|
jpayne@68
|
3763 images, which always have to be compressed. So if you don't want the
|
|
jpayne@68
|
3764 text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
|
|
jpayne@68
|
3765 Because tEXt and zTXt chunks don't have a language field, if you
|
|
jpayne@68
|
3766 specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
|
|
jpayne@68
|
3767 any language code or translated keyword will not be written out.
|
|
jpayne@68
|
3768
|
|
jpayne@68
|
3769 Until text gets around a few hundred bytes, it is not worth compressing it.
|
|
jpayne@68
|
3770 After the text has been written out to the file, the compression type
|
|
jpayne@68
|
3771 is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
|
|
jpayne@68
|
3772 so that it isn't written out again at the end (in case you are calling
|
|
jpayne@68
|
3773 png_write_end() with the same struct).
|
|
jpayne@68
|
3774
|
|
jpayne@68
|
3775 The keywords that are given in the PNG Specification are:
|
|
jpayne@68
|
3776
|
|
jpayne@68
|
3777 Title Short (one line) title or
|
|
jpayne@68
|
3778 caption for image
|
|
jpayne@68
|
3779
|
|
jpayne@68
|
3780 Author Name of image's creator
|
|
jpayne@68
|
3781
|
|
jpayne@68
|
3782 Description Description of image (possibly long)
|
|
jpayne@68
|
3783
|
|
jpayne@68
|
3784 Copyright Copyright notice
|
|
jpayne@68
|
3785
|
|
jpayne@68
|
3786 Creation Time Time of original image creation
|
|
jpayne@68
|
3787 (usually RFC 1123 format, see below)
|
|
jpayne@68
|
3788
|
|
jpayne@68
|
3789 Software Software used to create the image
|
|
jpayne@68
|
3790
|
|
jpayne@68
|
3791 Disclaimer Legal disclaimer
|
|
jpayne@68
|
3792
|
|
jpayne@68
|
3793 Warning Warning of nature of content
|
|
jpayne@68
|
3794
|
|
jpayne@68
|
3795 Source Device used to create the image
|
|
jpayne@68
|
3796
|
|
jpayne@68
|
3797 Comment Miscellaneous comment; conversion
|
|
jpayne@68
|
3798 from other image format
|
|
jpayne@68
|
3799
|
|
jpayne@68
|
3800 The keyword-text pairs work like this. Keywords should be short
|
|
jpayne@68
|
3801 simple descriptions of what the comment is about. Some typical
|
|
jpayne@68
|
3802 keywords are found in the PNG specification, as is some recommendations
|
|
jpayne@68
|
3803 on keywords. You can repeat keywords in a file. You can even write
|
|
jpayne@68
|
3804 some text before the image and some after. For example, you may want
|
|
jpayne@68
|
3805 to put a description of the image before the image, but leave the
|
|
jpayne@68
|
3806 disclaimer until after, so viewers working over modem connections
|
|
jpayne@68
|
3807 don't have to wait for the disclaimer to go over the modem before
|
|
jpayne@68
|
3808 they start seeing the image. Finally, keywords should be full
|
|
jpayne@68
|
3809 words, not abbreviations. Keywords and text are in the ISO 8859-1
|
|
jpayne@68
|
3810 (Latin-1) character set (a superset of regular ASCII) and can not
|
|
jpayne@68
|
3811 contain NUL characters, and should not contain control or other
|
|
jpayne@68
|
3812 unprintable characters. To make the comments widely readable, stick
|
|
jpayne@68
|
3813 with basic ASCII, and avoid machine specific character set extensions
|
|
jpayne@68
|
3814 like the IBM-PC character set. The keyword must be present, but
|
|
jpayne@68
|
3815 you can leave off the text string on non-compressed pairs.
|
|
jpayne@68
|
3816 Compressed pairs must have a text string, as only the text string
|
|
jpayne@68
|
3817 is compressed anyway, so the compression would be meaningless.
|
|
jpayne@68
|
3818
|
|
jpayne@68
|
3819 PNG supports modification time via the png_time structure. Two
|
|
jpayne@68
|
3820 conversion routines are provided, png_convert_from_time_t() for
|
|
jpayne@68
|
3821 time_t and png_convert_from_struct_tm() for struct tm. The
|
|
jpayne@68
|
3822 time_t routine uses gmtime(). You don't have to use either of
|
|
jpayne@68
|
3823 these, but if you wish to fill in the png_time structure directly,
|
|
jpayne@68
|
3824 you should provide the time in universal time (GMT) if possible
|
|
jpayne@68
|
3825 instead of your local time. Note that the year number is the full
|
|
jpayne@68
|
3826 year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
|
|
jpayne@68
|
3827 that months start with 1.
|
|
jpayne@68
|
3828
|
|
jpayne@68
|
3829 If you want to store the time of the original image creation, you should
|
|
jpayne@68
|
3830 use a plain tEXt chunk with the "Creation Time" keyword. This is
|
|
jpayne@68
|
3831 necessary because the "creation time" of a PNG image is somewhat vague,
|
|
jpayne@68
|
3832 depending on whether you mean the PNG file, the time the image was
|
|
jpayne@68
|
3833 created in a non-PNG format, a still photo from which the image was
|
|
jpayne@68
|
3834 scanned, or possibly the subject matter itself. In order to facilitate
|
|
jpayne@68
|
3835 machine-readable dates, it is recommended that the "Creation Time"
|
|
jpayne@68
|
3836 tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
|
|
jpayne@68
|
3837 although this isn't a requirement. Unlike the tIME chunk, the
|
|
jpayne@68
|
3838 "Creation Time" tEXt chunk is not expected to be automatically changed
|
|
jpayne@68
|
3839 by the software. To facilitate the use of RFC 1123 dates, a function
|
|
jpayne@68
|
3840 png_convert_to_rfc1123_buffer(buffer, png_timep) is provided to
|
|
jpayne@68
|
3841 convert from PNG time to an RFC 1123 format string. The caller must provide
|
|
jpayne@68
|
3842 a writeable buffer of at least 29 bytes.
|
|
jpayne@68
|
3843
|
|
jpayne@68
|
3844 .SS Writing unknown chunks
|
|
jpayne@68
|
3845
|
|
jpayne@68
|
3846 You can use the png_set_unknown_chunks function to queue up private chunks
|
|
jpayne@68
|
3847 for writing. You give it a chunk name, location, raw data, and a size. You
|
|
jpayne@68
|
3848 also must use png_set_keep_unknown_chunks() to ensure that libpng will
|
|
jpayne@68
|
3849 handle them. That's all there is to it. The chunks will be written by the
|
|
jpayne@68
|
3850 next following png_write_info_before_PLTE, png_write_info, or png_write_end
|
|
jpayne@68
|
3851 function, depending upon the specified location. Any chunks previously
|
|
jpayne@68
|
3852 read into the info structure's unknown-chunk list will also be written out
|
|
jpayne@68
|
3853 in a sequence that satisfies the PNG specification's ordering rules.
|
|
jpayne@68
|
3854
|
|
jpayne@68
|
3855 Here is an example of writing two private chunks, prVt and miNE:
|
|
jpayne@68
|
3856
|
|
jpayne@68
|
3857 #ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
|
|
jpayne@68
|
3858 /* Set unknown chunk data */
|
|
jpayne@68
|
3859 png_unknown_chunk unk_chunk[2];
|
|
jpayne@68
|
3860 strcpy((char *) unk_chunk[0].name, "prVt";
|
|
jpayne@68
|
3861 unk_chunk[0].data = (unsigned char *) "PRIVATE DATA";
|
|
jpayne@68
|
3862 unk_chunk[0].size = strlen(unk_chunk[0].data)+1;
|
|
jpayne@68
|
3863 unk_chunk[0].location = PNG_HAVE_IHDR;
|
|
jpayne@68
|
3864 strcpy((char *) unk_chunk[1].name, "miNE";
|
|
jpayne@68
|
3865 unk_chunk[1].data = (unsigned char *) "MY CHUNK DATA";
|
|
jpayne@68
|
3866 unk_chunk[1].size = strlen(unk_chunk[0].data)+1;
|
|
jpayne@68
|
3867 unk_chunk[1].location = PNG_AFTER_IDAT;
|
|
jpayne@68
|
3868 png_set_unknown_chunks(write_ptr, write_info_ptr,
|
|
jpayne@68
|
3869 unk_chunk, 2);
|
|
jpayne@68
|
3870 /* Needed because miNE is not safe-to-copy */
|
|
jpayne@68
|
3871 png_set_keep_unknown_chunks(png, PNG_HANDLE_CHUNK_ALWAYS,
|
|
jpayne@68
|
3872 (png_bytep) "miNE", 1);
|
|
jpayne@68
|
3873 # if PNG_LIBPNG_VER < 10600
|
|
jpayne@68
|
3874 /* Deal with unknown chunk location bug in 1.5.x and earlier */
|
|
jpayne@68
|
3875 png_set_unknown_chunk_location(png, info, 0, PNG_HAVE_IHDR);
|
|
jpayne@68
|
3876 png_set_unknown_chunk_location(png, info, 1, PNG_AFTER_IDAT);
|
|
jpayne@68
|
3877 # endif
|
|
jpayne@68
|
3878 # if PNG_LIBPNG_VER < 10500
|
|
jpayne@68
|
3879 /* PNG_AFTER_IDAT writes two copies of the chunk prior to libpng-1.5.0,
|
|
jpayne@68
|
3880 * one before IDAT and another after IDAT, so don't use it; only use
|
|
jpayne@68
|
3881 * PNG_HAVE_IHDR location. This call resets the location previously
|
|
jpayne@68
|
3882 * set by assignment and png_set_unknown_chunk_location() for chunk 1.
|
|
jpayne@68
|
3883 */
|
|
jpayne@68
|
3884 png_set_unknown_chunk_location(png, info, 1, PNG_HAVE_IHDR);
|
|
jpayne@68
|
3885 # endif
|
|
jpayne@68
|
3886 #endif
|
|
jpayne@68
|
3887
|
|
jpayne@68
|
3888 .SS The high-level write interface
|
|
jpayne@68
|
3889
|
|
jpayne@68
|
3890 At this point there are two ways to proceed; through the high-level
|
|
jpayne@68
|
3891 write interface, or through a sequence of low-level write operations.
|
|
jpayne@68
|
3892 You can use the high-level interface if your image data is present
|
|
jpayne@68
|
3893 in the info structure. All defined output
|
|
jpayne@68
|
3894 transformations are permitted, enabled by the following masks.
|
|
jpayne@68
|
3895
|
|
jpayne@68
|
3896 PNG_TRANSFORM_IDENTITY No transformation
|
|
jpayne@68
|
3897 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
|
|
jpayne@68
|
3898 PNG_TRANSFORM_PACKSWAP Change order of packed
|
|
jpayne@68
|
3899 pixels to LSB first
|
|
jpayne@68
|
3900 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
|
|
jpayne@68
|
3901 PNG_TRANSFORM_SHIFT Normalize pixels to the
|
|
jpayne@68
|
3902 sBIT depth
|
|
jpayne@68
|
3903 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
|
|
jpayne@68
|
3904 to BGRA
|
|
jpayne@68
|
3905 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
|
|
jpayne@68
|
3906 to AG
|
|
jpayne@68
|
3907 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
|
|
jpayne@68
|
3908 to transparency
|
|
jpayne@68
|
3909 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
|
|
jpayne@68
|
3910 PNG_TRANSFORM_STRIP_FILLER Strip out filler
|
|
jpayne@68
|
3911 bytes (deprecated).
|
|
jpayne@68
|
3912 PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
|
|
jpayne@68
|
3913 filler bytes
|
|
jpayne@68
|
3914 PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
|
|
jpayne@68
|
3915 filler bytes
|
|
jpayne@68
|
3916
|
|
jpayne@68
|
3917 If you have valid image data in the info structure (you can use
|
|
jpayne@68
|
3918 png_set_rows() to put image data in the info structure), simply do this:
|
|
jpayne@68
|
3919
|
|
jpayne@68
|
3920 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
|
|
jpayne@68
|
3921
|
|
jpayne@68
|
3922 where png_transforms is an integer containing the bitwise OR of some set of
|
|
jpayne@68
|
3923 transformation flags. This call is equivalent to png_write_info(),
|
|
jpayne@68
|
3924 followed the set of transformations indicated by the transform mask,
|
|
jpayne@68
|
3925 then png_write_image(), and finally png_write_end().
|
|
jpayne@68
|
3926
|
|
jpayne@68
|
3927 (The final parameter of this call is not yet used. Someday it might point
|
|
jpayne@68
|
3928 to transformation parameters required by some future output transform.)
|
|
jpayne@68
|
3929
|
|
jpayne@68
|
3930 You must use png_transforms and not call any png_set_transform() functions
|
|
jpayne@68
|
3931 when you use png_write_png().
|
|
jpayne@68
|
3932
|
|
jpayne@68
|
3933 .SS The low-level write interface
|
|
jpayne@68
|
3934
|
|
jpayne@68
|
3935 If you are going the low-level route instead, you are now ready to
|
|
jpayne@68
|
3936 write all the file information up to the actual image data. You do
|
|
jpayne@68
|
3937 this with a call to png_write_info().
|
|
jpayne@68
|
3938
|
|
jpayne@68
|
3939 png_write_info(png_ptr, info_ptr);
|
|
jpayne@68
|
3940
|
|
jpayne@68
|
3941 Note that there is one transformation you may need to do before
|
|
jpayne@68
|
3942 png_write_info(). In PNG files, the alpha channel in an image is the
|
|
jpayne@68
|
3943 level of opacity. If your data is supplied as a level of transparency,
|
|
jpayne@68
|
3944 you can invert the alpha channel before you write it, so that 0 is
|
|
jpayne@68
|
3945 fully transparent and 255 (in 8-bit or paletted images) or 65535
|
|
jpayne@68
|
3946 (in 16-bit images) is fully opaque, with
|
|
jpayne@68
|
3947
|
|
jpayne@68
|
3948 png_set_invert_alpha(png_ptr);
|
|
jpayne@68
|
3949
|
|
jpayne@68
|
3950 This must appear before png_write_info() instead of later with the
|
|
jpayne@68
|
3951 other transformations because in the case of paletted images the tRNS
|
|
jpayne@68
|
3952 chunk data has to be inverted before the tRNS chunk is written. If
|
|
jpayne@68
|
3953 your image is not a paletted image, the tRNS data (which in such cases
|
|
jpayne@68
|
3954 represents a single color to be rendered as transparent) won't need to
|
|
jpayne@68
|
3955 be changed, and you can safely do this transformation after your
|
|
jpayne@68
|
3956 png_write_info() call.
|
|
jpayne@68
|
3957
|
|
jpayne@68
|
3958 If you need to write a private chunk that you want to appear before
|
|
jpayne@68
|
3959 the PLTE chunk when PLTE is present, you can write the PNG info in
|
|
jpayne@68
|
3960 two steps, and insert code to write your own chunk between them:
|
|
jpayne@68
|
3961
|
|
jpayne@68
|
3962 png_write_info_before_PLTE(png_ptr, info_ptr);
|
|
jpayne@68
|
3963 png_set_unknown_chunks(png_ptr, info_ptr, ...);
|
|
jpayne@68
|
3964 png_write_info(png_ptr, info_ptr);
|
|
jpayne@68
|
3965
|
|
jpayne@68
|
3966 After you've written the file information, you can set up the library
|
|
jpayne@68
|
3967 to handle any special transformations of the image data. The various
|
|
jpayne@68
|
3968 ways to transform the data will be described in the order that they
|
|
jpayne@68
|
3969 should occur. This is important, as some of these change the color
|
|
jpayne@68
|
3970 type and/or bit depth of the data, and some others only work on
|
|
jpayne@68
|
3971 certain color types and bit depths. Even though each transformation
|
|
jpayne@68
|
3972 checks to see if it has data that it can do something with, you should
|
|
jpayne@68
|
3973 make sure to only enable a transformation if it will be valid for the
|
|
jpayne@68
|
3974 data. For example, don't swap red and blue on grayscale data.
|
|
jpayne@68
|
3975
|
|
jpayne@68
|
3976 PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
|
|
jpayne@68
|
3977 the library to strip input data that has 4 or 8 bytes per pixel down
|
|
jpayne@68
|
3978 to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
|
|
jpayne@68
|
3979 bytes per pixel).
|
|
jpayne@68
|
3980
|
|
jpayne@68
|
3981 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
|
|
jpayne@68
|
3982
|
|
jpayne@68
|
3983 where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
|
|
jpayne@68
|
3984 PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
|
|
jpayne@68
|
3985 is stored XRGB or RGBX.
|
|
jpayne@68
|
3986
|
|
jpayne@68
|
3987 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
|
|
jpayne@68
|
3988 they can, resulting in, for example, 8 pixels per byte for 1 bit files.
|
|
jpayne@68
|
3989 If the data is supplied at 1 pixel per byte, use this code, which will
|
|
jpayne@68
|
3990 correctly pack the pixels into a single byte:
|
|
jpayne@68
|
3991
|
|
jpayne@68
|
3992 png_set_packing(png_ptr);
|
|
jpayne@68
|
3993
|
|
jpayne@68
|
3994 PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
|
|
jpayne@68
|
3995 data is of another bit depth, you can write an sBIT chunk into the
|
|
jpayne@68
|
3996 file so that decoders can recover the original data if desired.
|
|
jpayne@68
|
3997
|
|
jpayne@68
|
3998 /* Set the true bit depth of the image data */
|
|
jpayne@68
|
3999 if (color_type & PNG_COLOR_MASK_COLOR)
|
|
jpayne@68
|
4000 {
|
|
jpayne@68
|
4001 sig_bit.red = true_bit_depth;
|
|
jpayne@68
|
4002 sig_bit.green = true_bit_depth;
|
|
jpayne@68
|
4003 sig_bit.blue = true_bit_depth;
|
|
jpayne@68
|
4004 }
|
|
jpayne@68
|
4005
|
|
jpayne@68
|
4006 else
|
|
jpayne@68
|
4007 {
|
|
jpayne@68
|
4008 sig_bit.gray = true_bit_depth;
|
|
jpayne@68
|
4009 }
|
|
jpayne@68
|
4010
|
|
jpayne@68
|
4011 if (color_type & PNG_COLOR_MASK_ALPHA)
|
|
jpayne@68
|
4012 {
|
|
jpayne@68
|
4013 sig_bit.alpha = true_bit_depth;
|
|
jpayne@68
|
4014 }
|
|
jpayne@68
|
4015
|
|
jpayne@68
|
4016 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
|
|
jpayne@68
|
4017
|
|
jpayne@68
|
4018 If the data is stored in the row buffer in a bit depth other than
|
|
jpayne@68
|
4019 one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
|
|
jpayne@68
|
4020 this will scale the values to appear to be the correct bit depth as
|
|
jpayne@68
|
4021 is required by PNG.
|
|
jpayne@68
|
4022
|
|
jpayne@68
|
4023 png_set_shift(png_ptr, &sig_bit);
|
|
jpayne@68
|
4024
|
|
jpayne@68
|
4025 PNG files store 16-bit pixels in network byte order (big-endian,
|
|
jpayne@68
|
4026 ie. most significant bits first). This code would be used if they are
|
|
jpayne@68
|
4027 supplied the other way (little-endian, i.e. least significant bits
|
|
jpayne@68
|
4028 first, the way PCs store them):
|
|
jpayne@68
|
4029
|
|
jpayne@68
|
4030 if (bit_depth > 8)
|
|
jpayne@68
|
4031 png_set_swap(png_ptr);
|
|
jpayne@68
|
4032
|
|
jpayne@68
|
4033 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
|
|
jpayne@68
|
4034 need to change the order the pixels are packed into bytes, you can use:
|
|
jpayne@68
|
4035
|
|
jpayne@68
|
4036 if (bit_depth < 8)
|
|
jpayne@68
|
4037 png_set_packswap(png_ptr);
|
|
jpayne@68
|
4038
|
|
jpayne@68
|
4039 PNG files store 3 color pixels in red, green, blue order. This code
|
|
jpayne@68
|
4040 would be used if they are supplied as blue, green, red:
|
|
jpayne@68
|
4041
|
|
jpayne@68
|
4042 png_set_bgr(png_ptr);
|
|
jpayne@68
|
4043
|
|
jpayne@68
|
4044 PNG files describe monochrome as black being zero and white being
|
|
jpayne@68
|
4045 one. This code would be used if the pixels are supplied with this reversed
|
|
jpayne@68
|
4046 (black being one and white being zero):
|
|
jpayne@68
|
4047
|
|
jpayne@68
|
4048 png_set_invert_mono(png_ptr);
|
|
jpayne@68
|
4049
|
|
jpayne@68
|
4050 Finally, you can write your own transformation function if none of
|
|
jpayne@68
|
4051 the existing ones meets your needs. This is done by setting a callback
|
|
jpayne@68
|
4052 with
|
|
jpayne@68
|
4053
|
|
jpayne@68
|
4054 png_set_write_user_transform_fn(png_ptr,
|
|
jpayne@68
|
4055 write_transform_fn);
|
|
jpayne@68
|
4056
|
|
jpayne@68
|
4057 You must supply the function
|
|
jpayne@68
|
4058
|
|
jpayne@68
|
4059 void write_transform_fn(png_structp png_ptr, png_row_infop
|
|
jpayne@68
|
4060 row_info, png_bytep data)
|
|
jpayne@68
|
4061
|
|
jpayne@68
|
4062 See pngtest.c for a working example. Your function will be called
|
|
jpayne@68
|
4063 before any of the other transformations are processed. If supported
|
|
jpayne@68
|
4064 libpng also supplies an information routine that may be called from
|
|
jpayne@68
|
4065 your callback:
|
|
jpayne@68
|
4066
|
|
jpayne@68
|
4067 png_get_current_row_number(png_ptr);
|
|
jpayne@68
|
4068 png_get_current_pass_number(png_ptr);
|
|
jpayne@68
|
4069
|
|
jpayne@68
|
4070 This returns the current row passed to the transform. With interlaced
|
|
jpayne@68
|
4071 images the value returned is the row in the input sub-image image. Use
|
|
jpayne@68
|
4072 PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
|
|
jpayne@68
|
4073 find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
|
|
jpayne@68
|
4074
|
|
jpayne@68
|
4075 The discussion of interlace handling above contains more information on how to
|
|
jpayne@68
|
4076 use these values.
|
|
jpayne@68
|
4077
|
|
jpayne@68
|
4078 You can also set up a pointer to a user structure for use by your
|
|
jpayne@68
|
4079 callback function.
|
|
jpayne@68
|
4080
|
|
jpayne@68
|
4081 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
|
|
jpayne@68
|
4082
|
|
jpayne@68
|
4083 The user_channels and user_depth parameters of this function are ignored
|
|
jpayne@68
|
4084 when writing; you can set them to zero as shown.
|
|
jpayne@68
|
4085
|
|
jpayne@68
|
4086 You can retrieve the pointer via the function png_get_user_transform_ptr().
|
|
jpayne@68
|
4087 For example:
|
|
jpayne@68
|
4088
|
|
jpayne@68
|
4089 voidp write_user_transform_ptr =
|
|
jpayne@68
|
4090 png_get_user_transform_ptr(png_ptr);
|
|
jpayne@68
|
4091
|
|
jpayne@68
|
4092 It is possible to have libpng flush any pending output, either manually,
|
|
jpayne@68
|
4093 or automatically after a certain number of lines have been written. To
|
|
jpayne@68
|
4094 flush the output stream a single time call:
|
|
jpayne@68
|
4095
|
|
jpayne@68
|
4096 png_write_flush(png_ptr);
|
|
jpayne@68
|
4097
|
|
jpayne@68
|
4098 and to have libpng flush the output stream periodically after a certain
|
|
jpayne@68
|
4099 number of scanlines have been written, call:
|
|
jpayne@68
|
4100
|
|
jpayne@68
|
4101 png_set_flush(png_ptr, nrows);
|
|
jpayne@68
|
4102
|
|
jpayne@68
|
4103 Note that the distance between rows is from the last time png_write_flush()
|
|
jpayne@68
|
4104 was called, or the first row of the image if it has never been called.
|
|
jpayne@68
|
4105 So if you write 50 lines, and then png_set_flush 25, it will flush the
|
|
jpayne@68
|
4106 output on the next scanline, and every 25 lines thereafter, unless
|
|
jpayne@68
|
4107 png_write_flush() is called before 25 more lines have been written.
|
|
jpayne@68
|
4108 If nrows is too small (less than about 10 lines for a 640 pixel wide
|
|
jpayne@68
|
4109 RGB image) the image compression may decrease noticeably (although this
|
|
jpayne@68
|
4110 may be acceptable for real-time applications). Infrequent flushing will
|
|
jpayne@68
|
4111 only degrade the compression performance by a few percent over images
|
|
jpayne@68
|
4112 that do not use flushing.
|
|
jpayne@68
|
4113
|
|
jpayne@68
|
4114 .SS Writing the image data
|
|
jpayne@68
|
4115
|
|
jpayne@68
|
4116 That's it for the transformations. Now you can write the image data.
|
|
jpayne@68
|
4117 The simplest way to do this is in one function call. If you have the
|
|
jpayne@68
|
4118 whole image in memory, you can just call png_write_image() and libpng
|
|
jpayne@68
|
4119 will write the image. You will need to pass in an array of pointers to
|
|
jpayne@68
|
4120 each row. This function automatically handles interlacing, so you don't
|
|
jpayne@68
|
4121 need to call png_set_interlace_handling() or call this function multiple
|
|
jpayne@68
|
4122 times, or any of that other stuff necessary with png_write_rows().
|
|
jpayne@68
|
4123
|
|
jpayne@68
|
4124 png_write_image(png_ptr, row_pointers);
|
|
jpayne@68
|
4125
|
|
jpayne@68
|
4126 where row_pointers is:
|
|
jpayne@68
|
4127
|
|
jpayne@68
|
4128 png_byte *row_pointers[height];
|
|
jpayne@68
|
4129
|
|
jpayne@68
|
4130 You can point to void or char or whatever you use for pixels.
|
|
jpayne@68
|
4131
|
|
jpayne@68
|
4132 If you don't want to write the whole image at once, you can
|
|
jpayne@68
|
4133 use png_write_rows() instead. If the file is not interlaced,
|
|
jpayne@68
|
4134 this is simple:
|
|
jpayne@68
|
4135
|
|
jpayne@68
|
4136 png_write_rows(png_ptr, row_pointers,
|
|
jpayne@68
|
4137 number_of_rows);
|
|
jpayne@68
|
4138
|
|
jpayne@68
|
4139 row_pointers is the same as in the png_write_image() call.
|
|
jpayne@68
|
4140
|
|
jpayne@68
|
4141 If you are just writing one row at a time, you can do this with
|
|
jpayne@68
|
4142 a single row_pointer instead of an array of row_pointers:
|
|
jpayne@68
|
4143
|
|
jpayne@68
|
4144 png_bytep row_pointer = row;
|
|
jpayne@68
|
4145
|
|
jpayne@68
|
4146 png_write_row(png_ptr, row_pointer);
|
|
jpayne@68
|
4147
|
|
jpayne@68
|
4148 When the file is interlaced, things can get a good deal more complicated.
|
|
jpayne@68
|
4149 The only currently (as of the PNG Specification version 1.2, dated July
|
|
jpayne@68
|
4150 1999) defined interlacing scheme for PNG files is the "Adam7" interlace
|
|
jpayne@68
|
4151 scheme, that breaks down an image into seven smaller images of varying
|
|
jpayne@68
|
4152 size. libpng will build these images for you, or you can do them
|
|
jpayne@68
|
4153 yourself. If you want to build them yourself, see the PNG specification
|
|
jpayne@68
|
4154 for details of which pixels to write when.
|
|
jpayne@68
|
4155
|
|
jpayne@68
|
4156 If you don't want libpng to handle the interlacing details, just
|
|
jpayne@68
|
4157 use png_set_interlace_handling() and call png_write_rows() the
|
|
jpayne@68
|
4158 correct number of times to write all the sub-images
|
|
jpayne@68
|
4159 (png_set_interlace_handling() returns the number of sub-images.)
|
|
jpayne@68
|
4160
|
|
jpayne@68
|
4161 If you want libpng to build the sub-images, call this before you start
|
|
jpayne@68
|
4162 writing any rows:
|
|
jpayne@68
|
4163
|
|
jpayne@68
|
4164 number_of_passes = png_set_interlace_handling(png_ptr);
|
|
jpayne@68
|
4165
|
|
jpayne@68
|
4166 This will return the number of passes needed. Currently, this is seven,
|
|
jpayne@68
|
4167 but may change if another interlace type is added.
|
|
jpayne@68
|
4168
|
|
jpayne@68
|
4169 Then write the complete image number_of_passes times.
|
|
jpayne@68
|
4170
|
|
jpayne@68
|
4171 png_write_rows(png_ptr, row_pointers, number_of_rows);
|
|
jpayne@68
|
4172
|
|
jpayne@68
|
4173 Think carefully before you write an interlaced image. Typically code that
|
|
jpayne@68
|
4174 reads such images reads all the image data into memory, uncompressed, before
|
|
jpayne@68
|
4175 doing any processing. Only code that can display an image on the fly can
|
|
jpayne@68
|
4176 take advantage of the interlacing and even then the image has to be exactly
|
|
jpayne@68
|
4177 the correct size for the output device, because scaling an image requires
|
|
jpayne@68
|
4178 adjacent pixels and these are not available until all the passes have been
|
|
jpayne@68
|
4179 read.
|
|
jpayne@68
|
4180
|
|
jpayne@68
|
4181 If you do write an interlaced image you will hardly ever need to handle
|
|
jpayne@68
|
4182 the interlacing yourself. Call png_set_interlace_handling() and use the
|
|
jpayne@68
|
4183 approach described above.
|
|
jpayne@68
|
4184
|
|
jpayne@68
|
4185 The only time it is conceivable that you will really need to write an
|
|
jpayne@68
|
4186 interlaced image pass-by-pass is when you have read one pass by pass and
|
|
jpayne@68
|
4187 made some pixel-by-pixel transformation to it, as described in the read
|
|
jpayne@68
|
4188 code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros
|
|
jpayne@68
|
4189 to determine the size of each sub-image in turn and simply write the rows
|
|
jpayne@68
|
4190 you obtained from the read code.
|
|
jpayne@68
|
4191
|
|
jpayne@68
|
4192 .SS Finishing a sequential write
|
|
jpayne@68
|
4193
|
|
jpayne@68
|
4194 After you are finished writing the image, you should finish writing
|
|
jpayne@68
|
4195 the file. If you are interested in writing comments or time, you should
|
|
jpayne@68
|
4196 pass an appropriately filled png_info pointer. If you are not interested,
|
|
jpayne@68
|
4197 you can pass NULL.
|
|
jpayne@68
|
4198
|
|
jpayne@68
|
4199 png_write_end(png_ptr, info_ptr);
|
|
jpayne@68
|
4200
|
|
jpayne@68
|
4201 When you are done, you can free all memory used by libpng like this:
|
|
jpayne@68
|
4202
|
|
jpayne@68
|
4203 png_destroy_write_struct(&png_ptr, &info_ptr);
|
|
jpayne@68
|
4204
|
|
jpayne@68
|
4205 It is also possible to individually free the info_ptr members that
|
|
jpayne@68
|
4206 point to libpng-allocated storage with the following function:
|
|
jpayne@68
|
4207
|
|
jpayne@68
|
4208 png_free_data(png_ptr, info_ptr, mask, seq)
|
|
jpayne@68
|
4209
|
|
jpayne@68
|
4210 mask - identifies data to be freed, a mask
|
|
jpayne@68
|
4211 containing the bitwise OR of one or
|
|
jpayne@68
|
4212 more of
|
|
jpayne@68
|
4213 PNG_FREE_PLTE, PNG_FREE_TRNS,
|
|
jpayne@68
|
4214 PNG_FREE_HIST, PNG_FREE_ICCP,
|
|
jpayne@68
|
4215 PNG_FREE_PCAL, PNG_FREE_ROWS,
|
|
jpayne@68
|
4216 PNG_FREE_SCAL, PNG_FREE_SPLT,
|
|
jpayne@68
|
4217 PNG_FREE_TEXT, PNG_FREE_UNKN,
|
|
jpayne@68
|
4218 or simply PNG_FREE_ALL
|
|
jpayne@68
|
4219
|
|
jpayne@68
|
4220 seq - sequence number of item to be freed
|
|
jpayne@68
|
4221 (\-1 for all items)
|
|
jpayne@68
|
4222
|
|
jpayne@68
|
4223 This function may be safely called when the relevant storage has
|
|
jpayne@68
|
4224 already been freed, or has not yet been allocated, or was allocated
|
|
jpayne@68
|
4225 by the user and not by libpng, and will in those cases do nothing.
|
|
jpayne@68
|
4226 The "seq" parameter is ignored if only one item of the selected data
|
|
jpayne@68
|
4227 type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items
|
|
jpayne@68
|
4228 are allowed for the data type identified in the mask, such as text or
|
|
jpayne@68
|
4229 sPLT, only the n'th item in the structure is freed, where n is "seq".
|
|
jpayne@68
|
4230
|
|
jpayne@68
|
4231 If you allocated data such as a palette that you passed in to libpng
|
|
jpayne@68
|
4232 with png_set_*, you must not free it until just before the call to
|
|
jpayne@68
|
4233 png_destroy_write_struct().
|
|
jpayne@68
|
4234
|
|
jpayne@68
|
4235 The default behavior is only to free data that was allocated internally
|
|
jpayne@68
|
4236 by libpng. This can be changed, so that libpng will not free the data,
|
|
jpayne@68
|
4237 or so that it will free data that was allocated by the user with png_malloc()
|
|
jpayne@68
|
4238 or png_calloc() and passed in via a png_set_*() function, with
|
|
jpayne@68
|
4239
|
|
jpayne@68
|
4240 png_data_freer(png_ptr, info_ptr, freer, mask)
|
|
jpayne@68
|
4241
|
|
jpayne@68
|
4242 freer - one of
|
|
jpayne@68
|
4243 PNG_DESTROY_WILL_FREE_DATA
|
|
jpayne@68
|
4244 PNG_SET_WILL_FREE_DATA
|
|
jpayne@68
|
4245 PNG_USER_WILL_FREE_DATA
|
|
jpayne@68
|
4246
|
|
jpayne@68
|
4247 mask - which data elements are affected
|
|
jpayne@68
|
4248 same choices as in png_free_data()
|
|
jpayne@68
|
4249
|
|
jpayne@68
|
4250 For example, to transfer responsibility for some data from a read structure
|
|
jpayne@68
|
4251 to a write structure, you could use
|
|
jpayne@68
|
4252
|
|
jpayne@68
|
4253 png_data_freer(read_ptr, read_info_ptr,
|
|
jpayne@68
|
4254 PNG_USER_WILL_FREE_DATA,
|
|
jpayne@68
|
4255 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
|
|
jpayne@68
|
4256
|
|
jpayne@68
|
4257 png_data_freer(write_ptr, write_info_ptr,
|
|
jpayne@68
|
4258 PNG_DESTROY_WILL_FREE_DATA,
|
|
jpayne@68
|
4259 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
|
|
jpayne@68
|
4260
|
|
jpayne@68
|
4261 thereby briefly reassigning responsibility for freeing to the user but
|
|
jpayne@68
|
4262 immediately afterwards reassigning it once more to the write_destroy
|
|
jpayne@68
|
4263 function. Having done this, it would then be safe to destroy the read
|
|
jpayne@68
|
4264 structure and continue to use the PLTE, tRNS, and hIST data in the write
|
|
jpayne@68
|
4265 structure.
|
|
jpayne@68
|
4266
|
|
jpayne@68
|
4267 This function only affects data that has already been allocated.
|
|
jpayne@68
|
4268 You can call this function before calling after the png_set_*() functions
|
|
jpayne@68
|
4269 to control whether the user or png_destroy_*() is supposed to free the data.
|
|
jpayne@68
|
4270 When the user assumes responsibility for libpng-allocated data, the
|
|
jpayne@68
|
4271 application must use
|
|
jpayne@68
|
4272 png_free() to free it, and when the user transfers responsibility to libpng
|
|
jpayne@68
|
4273 for data that the user has allocated, the user must have used png_malloc()
|
|
jpayne@68
|
4274 or png_calloc() to allocate it.
|
|
jpayne@68
|
4275
|
|
jpayne@68
|
4276 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
|
|
jpayne@68
|
4277 separately, do not transfer responsibility for freeing text_ptr to libpng,
|
|
jpayne@68
|
4278 because when libpng fills a png_text structure it combines these members with
|
|
jpayne@68
|
4279 the key member, and png_free_data() will free only text_ptr.key. Similarly,
|
|
jpayne@68
|
4280 if you transfer responsibility for free'ing text_ptr from libpng to your
|
|
jpayne@68
|
4281 application, your application must not separately free those members.
|
|
jpayne@68
|
4282 For a more compact example of writing a PNG image, see the file example.c.
|
|
jpayne@68
|
4283
|
|
jpayne@68
|
4284 .SH V. Simplified API
|
|
jpayne@68
|
4285
|
|
jpayne@68
|
4286 The simplified API, which became available in libpng-1.6.0, hides the details
|
|
jpayne@68
|
4287 of both libpng and the PNG file format itself.
|
|
jpayne@68
|
4288 It allows PNG files to be read into a very limited number of
|
|
jpayne@68
|
4289 in-memory bitmap formats or to be written from the same formats. If these
|
|
jpayne@68
|
4290 formats do not accommodate your needs then you can, and should, use the more
|
|
jpayne@68
|
4291 sophisticated APIs above - these support a wide variety of in-memory formats
|
|
jpayne@68
|
4292 and a wide variety of sophisticated transformations to those formats as well
|
|
jpayne@68
|
4293 as a wide variety of APIs to manipulate ancillary information.
|
|
jpayne@68
|
4294
|
|
jpayne@68
|
4295 To read a PNG file using the simplified API:
|
|
jpayne@68
|
4296
|
|
jpayne@68
|
4297 1) Declare a 'png_image' structure (see below) on the stack, set the
|
|
jpayne@68
|
4298 version field to PNG_IMAGE_VERSION and the 'opaque' pointer to NULL
|
|
jpayne@68
|
4299 (this is REQUIRED, your program may crash if you don't do it.)
|
|
jpayne@68
|
4300
|
|
jpayne@68
|
4301 2) Call the appropriate png_image_begin_read... function.
|
|
jpayne@68
|
4302
|
|
jpayne@68
|
4303 3) Set the png_image 'format' member to the required sample format.
|
|
jpayne@68
|
4304
|
|
jpayne@68
|
4305 4) Allocate a buffer for the image and, if required, the color-map.
|
|
jpayne@68
|
4306
|
|
jpayne@68
|
4307 5) Call png_image_finish_read to read the image and, if required, the
|
|
jpayne@68
|
4308 color-map into your buffers.
|
|
jpayne@68
|
4309
|
|
jpayne@68
|
4310 There are no restrictions on the format of the PNG input itself; all valid
|
|
jpayne@68
|
4311 color types, bit depths, and interlace methods are acceptable, and the
|
|
jpayne@68
|
4312 input image is transformed as necessary to the requested in-memory format
|
|
jpayne@68
|
4313 during the png_image_finish_read() step. The only caveat is that if you
|
|
jpayne@68
|
4314 request a color-mapped image from a PNG that is full-color or makes
|
|
jpayne@68
|
4315 complex use of an alpha channel the transformation is extremely lossy and the
|
|
jpayne@68
|
4316 result may look terrible.
|
|
jpayne@68
|
4317
|
|
jpayne@68
|
4318 To write a PNG file using the simplified API:
|
|
jpayne@68
|
4319
|
|
jpayne@68
|
4320 1) Declare a 'png_image' structure on the stack and memset()
|
|
jpayne@68
|
4321 it to all zero.
|
|
jpayne@68
|
4322
|
|
jpayne@68
|
4323 2) Initialize the members of the structure that describe the
|
|
jpayne@68
|
4324 image, setting the 'format' member to the format of the
|
|
jpayne@68
|
4325 image samples.
|
|
jpayne@68
|
4326
|
|
jpayne@68
|
4327 3) Call the appropriate png_image_write... function with a
|
|
jpayne@68
|
4328 pointer to the image and, if necessary, the color-map to write
|
|
jpayne@68
|
4329 the PNG data.
|
|
jpayne@68
|
4330
|
|
jpayne@68
|
4331 png_image is a structure that describes the in-memory format of an image
|
|
jpayne@68
|
4332 when it is being read or defines the in-memory format of an image that you
|
|
jpayne@68
|
4333 need to write. The "png_image" structure contains the following members:
|
|
jpayne@68
|
4334
|
|
jpayne@68
|
4335 png_controlp opaque Initialize to NULL, free with png_image_free
|
|
jpayne@68
|
4336 png_uint_32 version Set to PNG_IMAGE_VERSION
|
|
jpayne@68
|
4337 png_uint_32 width Image width in pixels (columns)
|
|
jpayne@68
|
4338 png_uint_32 height Image height in pixels (rows)
|
|
jpayne@68
|
4339 png_uint_32 format Image format as defined below
|
|
jpayne@68
|
4340 png_uint_32 flags A bit mask containing informational flags
|
|
jpayne@68
|
4341 png_uint_32 colormap_entries; Number of entries in the color-map
|
|
jpayne@68
|
4342 png_uint_32 warning_or_error;
|
|
jpayne@68
|
4343 char message[64];
|
|
jpayne@68
|
4344
|
|
jpayne@68
|
4345 In the event of an error or warning the "warning_or_error"
|
|
jpayne@68
|
4346 field will be set to a non-zero value and the 'message' field will contain
|
|
jpayne@68
|
4347 a '\0' terminated string with the libpng error or warning message. If both
|
|
jpayne@68
|
4348 warnings and an error were encountered, only the error is recorded. If there
|
|
jpayne@68
|
4349 are multiple warnings, only the first one is recorded.
|
|
jpayne@68
|
4350
|
|
jpayne@68
|
4351 The upper 30 bits of the "warning_or_error" value are reserved; the low two
|
|
jpayne@68
|
4352 bits contain a two bit code such that a value more than 1 indicates a failure
|
|
jpayne@68
|
4353 in the API just called:
|
|
jpayne@68
|
4354
|
|
jpayne@68
|
4355 0 - no warning or error
|
|
jpayne@68
|
4356 1 - warning
|
|
jpayne@68
|
4357 2 - error
|
|
jpayne@68
|
4358 3 - error preceded by warning
|
|
jpayne@68
|
4359
|
|
jpayne@68
|
4360 The pixels (samples) of the image have one to four channels whose components
|
|
jpayne@68
|
4361 have original values in the range 0 to 1.0:
|
|
jpayne@68
|
4362
|
|
jpayne@68
|
4363 1: A single gray or luminance channel (G).
|
|
jpayne@68
|
4364 2: A gray/luminance channel and an alpha channel (GA).
|
|
jpayne@68
|
4365 3: Three red, green, blue color channels (RGB).
|
|
jpayne@68
|
4366 4: Three color channels and an alpha channel (RGBA).
|
|
jpayne@68
|
4367
|
|
jpayne@68
|
4368 The channels are encoded in one of two ways:
|
|
jpayne@68
|
4369
|
|
jpayne@68
|
4370 a) As a small integer, value 0..255, contained in a single byte. For the
|
|
jpayne@68
|
4371 alpha channel the original value is simply value/255. For the color or
|
|
jpayne@68
|
4372 luminance channels the value is encoded according to the sRGB specification
|
|
jpayne@68
|
4373 and matches the 8-bit format expected by typical display devices.
|
|
jpayne@68
|
4374
|
|
jpayne@68
|
4375 The color/gray channels are not scaled (pre-multiplied) by the alpha
|
|
jpayne@68
|
4376 channel and are suitable for passing to color management software.
|
|
jpayne@68
|
4377
|
|
jpayne@68
|
4378 b) As a value in the range 0..65535, contained in a 2-byte integer, in
|
|
jpayne@68
|
4379 the native byte order of the platform on which the application is running.
|
|
jpayne@68
|
4380 All channels can be converted to the original value by dividing by 65535; all
|
|
jpayne@68
|
4381 channels are linear. Color channels use the RGB encoding (RGB end-points) of
|
|
jpayne@68
|
4382 the sRGB specification. This encoding is identified by the
|
|
jpayne@68
|
4383 PNG_FORMAT_FLAG_LINEAR flag below.
|
|
jpayne@68
|
4384
|
|
jpayne@68
|
4385 When the simplified API needs to convert between sRGB and linear colorspaces,
|
|
jpayne@68
|
4386 the actual sRGB transfer curve defined in the sRGB specification (see the
|
|
jpayne@68
|
4387 article at https://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2
|
|
jpayne@68
|
4388 approximation used elsewhere in libpng.
|
|
jpayne@68
|
4389
|
|
jpayne@68
|
4390 When an alpha channel is present it is expected to denote pixel coverage
|
|
jpayne@68
|
4391 of the color or luminance channels and is returned as an associated alpha
|
|
jpayne@68
|
4392 channel: the color/gray channels are scaled (pre-multiplied) by the alpha
|
|
jpayne@68
|
4393 value.
|
|
jpayne@68
|
4394
|
|
jpayne@68
|
4395 The samples are either contained directly in the image data, between 1 and 8
|
|
jpayne@68
|
4396 bytes per pixel according to the encoding, or are held in a color-map indexed
|
|
jpayne@68
|
4397 by bytes in the image data. In the case of a color-map the color-map entries
|
|
jpayne@68
|
4398 are individual samples, encoded as above, and the image data has one byte per
|
|
jpayne@68
|
4399 pixel to select the relevant sample from the color-map.
|
|
jpayne@68
|
4400
|
|
jpayne@68
|
4401 PNG_FORMAT_*
|
|
jpayne@68
|
4402
|
|
jpayne@68
|
4403 The #defines to be used in png_image::format. Each #define identifies a
|
|
jpayne@68
|
4404 particular layout of channel data and, if present, alpha values. There are
|
|
jpayne@68
|
4405 separate defines for each of the two component encodings.
|
|
jpayne@68
|
4406
|
|
jpayne@68
|
4407 A format is built up using single bit flag values. All combinations are
|
|
jpayne@68
|
4408 valid. Formats can be built up from the flag values or you can use one of
|
|
jpayne@68
|
4409 the predefined values below. When testing formats always use the FORMAT_FLAG
|
|
jpayne@68
|
4410 macros to test for individual features - future versions of the library may
|
|
jpayne@68
|
4411 add new flags.
|
|
jpayne@68
|
4412
|
|
jpayne@68
|
4413 When reading or writing color-mapped images the format should be set to the
|
|
jpayne@68
|
4414 format of the entries in the color-map then png_image_{read,write}_colormap
|
|
jpayne@68
|
4415 called to read or write the color-map and set the format correctly for the
|
|
jpayne@68
|
4416 image data. Do not set the PNG_FORMAT_FLAG_COLORMAP bit directly!
|
|
jpayne@68
|
4417
|
|
jpayne@68
|
4418 NOTE: libpng can be built with particular features disabled. If you see
|
|
jpayne@68
|
4419 compiler errors because the definition of one of the following flags has been
|
|
jpayne@68
|
4420 compiled out it is because libpng does not have the required support. It is
|
|
jpayne@68
|
4421 possible, however, for the libpng configuration to enable the format on just
|
|
jpayne@68
|
4422 read or just write; in that case you may see an error at run time.
|
|
jpayne@68
|
4423 You can guard against this by checking for the definition of the
|
|
jpayne@68
|
4424 appropriate "_SUPPORTED" macro, one of:
|
|
jpayne@68
|
4425
|
|
jpayne@68
|
4426 PNG_SIMPLIFIED_{READ,WRITE}_{BGR,AFIRST}_SUPPORTED
|
|
jpayne@68
|
4427
|
|
jpayne@68
|
4428 PNG_FORMAT_FLAG_ALPHA format with an alpha channel
|
|
jpayne@68
|
4429 PNG_FORMAT_FLAG_COLOR color format: otherwise grayscale
|
|
jpayne@68
|
4430 PNG_FORMAT_FLAG_LINEAR 2-byte channels else 1-byte
|
|
jpayne@68
|
4431 PNG_FORMAT_FLAG_COLORMAP image data is color-mapped
|
|
jpayne@68
|
4432 PNG_FORMAT_FLAG_BGR BGR colors, else order is RGB
|
|
jpayne@68
|
4433 PNG_FORMAT_FLAG_AFIRST alpha channel comes first
|
|
jpayne@68
|
4434
|
|
jpayne@68
|
4435 Supported formats are as follows. Future versions of libpng may support more
|
|
jpayne@68
|
4436 formats; for compatibility with older versions simply check if the format
|
|
jpayne@68
|
4437 macro is defined using #ifdef. These defines describe the in-memory layout
|
|
jpayne@68
|
4438 of the components of the pixels of the image.
|
|
jpayne@68
|
4439
|
|
jpayne@68
|
4440 First the single byte (sRGB) formats:
|
|
jpayne@68
|
4441
|
|
jpayne@68
|
4442 PNG_FORMAT_GRAY
|
|
jpayne@68
|
4443 PNG_FORMAT_GA
|
|
jpayne@68
|
4444 PNG_FORMAT_AG
|
|
jpayne@68
|
4445 PNG_FORMAT_RGB
|
|
jpayne@68
|
4446 PNG_FORMAT_BGR
|
|
jpayne@68
|
4447 PNG_FORMAT_RGBA
|
|
jpayne@68
|
4448 PNG_FORMAT_ARGB
|
|
jpayne@68
|
4449 PNG_FORMAT_BGRA
|
|
jpayne@68
|
4450 PNG_FORMAT_ABGR
|
|
jpayne@68
|
4451
|
|
jpayne@68
|
4452 Then the linear 2-byte formats. When naming these "Y" is used to
|
|
jpayne@68
|
4453 indicate a luminance (gray) channel. The component order within the pixel
|
|
jpayne@68
|
4454 is always the same - there is no provision for swapping the order of the
|
|
jpayne@68
|
4455 components in the linear format. The components are 16-bit integers in
|
|
jpayne@68
|
4456 the native byte order for your platform, and there is no provision for
|
|
jpayne@68
|
4457 swapping the bytes to a different endian condition.
|
|
jpayne@68
|
4458
|
|
jpayne@68
|
4459 PNG_FORMAT_LINEAR_Y
|
|
jpayne@68
|
4460 PNG_FORMAT_LINEAR_Y_ALPHA
|
|
jpayne@68
|
4461 PNG_FORMAT_LINEAR_RGB
|
|
jpayne@68
|
4462 PNG_FORMAT_LINEAR_RGB_ALPHA
|
|
jpayne@68
|
4463
|
|
jpayne@68
|
4464 With color-mapped formats the image data is one byte for each pixel. The byte
|
|
jpayne@68
|
4465 is an index into the color-map which is formatted as above. To obtain a
|
|
jpayne@68
|
4466 color-mapped format it is sufficient just to add the PNG_FOMAT_FLAG_COLORMAP
|
|
jpayne@68
|
4467 to one of the above definitions, or you can use one of the definitions below.
|
|
jpayne@68
|
4468
|
|
jpayne@68
|
4469 PNG_FORMAT_RGB_COLORMAP
|
|
jpayne@68
|
4470 PNG_FORMAT_BGR_COLORMAP
|
|
jpayne@68
|
4471 PNG_FORMAT_RGBA_COLORMAP
|
|
jpayne@68
|
4472 PNG_FORMAT_ARGB_COLORMAP
|
|
jpayne@68
|
4473 PNG_FORMAT_BGRA_COLORMAP
|
|
jpayne@68
|
4474 PNG_FORMAT_ABGR_COLORMAP
|
|
jpayne@68
|
4475
|
|
jpayne@68
|
4476 PNG_IMAGE macros
|
|
jpayne@68
|
4477
|
|
jpayne@68
|
4478 These are convenience macros to derive information from a png_image
|
|
jpayne@68
|
4479 structure. The PNG_IMAGE_SAMPLE_ macros return values appropriate to the
|
|
jpayne@68
|
4480 actual image sample values - either the entries in the color-map or the
|
|
jpayne@68
|
4481 pixels in the image. The PNG_IMAGE_PIXEL_ macros return corresponding values
|
|
jpayne@68
|
4482 for the pixels and will always return 1 for color-mapped formats. The
|
|
jpayne@68
|
4483 remaining macros return information about the rows in the image and the
|
|
jpayne@68
|
4484 complete image.
|
|
jpayne@68
|
4485
|
|
jpayne@68
|
4486 NOTE: All the macros that take a png_image::format parameter are compile time
|
|
jpayne@68
|
4487 constants if the format parameter is, itself, a constant. Therefore these
|
|
jpayne@68
|
4488 macros can be used in array declarations and case labels where required.
|
|
jpayne@68
|
4489 Similarly the macros are also pre-processor constants (sizeof is not used) so
|
|
jpayne@68
|
4490 they can be used in #if tests.
|
|
jpayne@68
|
4491
|
|
jpayne@68
|
4492 PNG_IMAGE_SAMPLE_CHANNELS(fmt)
|
|
jpayne@68
|
4493 Returns the total number of channels in a given format: 1..4
|
|
jpayne@68
|
4494
|
|
jpayne@68
|
4495 PNG_IMAGE_SAMPLE_COMPONENT_SIZE(fmt)
|
|
jpayne@68
|
4496 Returns the size in bytes of a single component of a pixel or color-map
|
|
jpayne@68
|
4497 entry (as appropriate) in the image: 1 or 2.
|
|
jpayne@68
|
4498
|
|
jpayne@68
|
4499 PNG_IMAGE_SAMPLE_SIZE(fmt)
|
|
jpayne@68
|
4500 This is the size of the sample data for one sample. If the image is
|
|
jpayne@68
|
4501 color-mapped it is the size of one color-map entry (and image pixels are
|
|
jpayne@68
|
4502 one byte in size), otherwise it is the size of one image pixel.
|
|
jpayne@68
|
4503
|
|
jpayne@68
|
4504 PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(fmt)
|
|
jpayne@68
|
4505 The maximum size of the color-map required by the format expressed in a
|
|
jpayne@68
|
4506 count of components. This can be used to compile-time allocate a
|
|
jpayne@68
|
4507 color-map:
|
|
jpayne@68
|
4508
|
|
jpayne@68
|
4509 png_uint_16 colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(linear_fmt)];
|
|
jpayne@68
|
4510
|
|
jpayne@68
|
4511 png_byte colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(sRGB_fmt)];
|
|
jpayne@68
|
4512
|
|
jpayne@68
|
4513 Alternatively use the PNG_IMAGE_COLORMAP_SIZE macro below to use the
|
|
jpayne@68
|
4514 information from one of the png_image_begin_read_ APIs and dynamically
|
|
jpayne@68
|
4515 allocate the required memory.
|
|
jpayne@68
|
4516
|
|
jpayne@68
|
4517 PNG_IMAGE_COLORMAP_SIZE(fmt)
|
|
jpayne@68
|
4518 The size of the color-map required by the format; this is the size of the
|
|
jpayne@68
|
4519 color-map buffer passed to the png_image_{read,write}_colormap APIs. It is
|
|
jpayne@68
|
4520 a fixed number determined by the format so can easily be allocated on the
|
|
jpayne@68
|
4521 stack if necessary.
|
|
jpayne@68
|
4522
|
|
jpayne@68
|
4523 Corresponding information about the pixels
|
|
jpayne@68
|
4524
|
|
jpayne@68
|
4525 PNG_IMAGE_PIXEL_CHANNELS(fmt)
|
|
jpayne@68
|
4526 The number of separate channels (components) in a pixel; 1 for a
|
|
jpayne@68
|
4527 color-mapped image.
|
|
jpayne@68
|
4528
|
|
jpayne@68
|
4529 PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt)\
|
|
jpayne@68
|
4530 The size, in bytes, of each component in a pixel; 1 for a color-mapped
|
|
jpayne@68
|
4531 image.
|
|
jpayne@68
|
4532
|
|
jpayne@68
|
4533 PNG_IMAGE_PIXEL_SIZE(fmt)
|
|
jpayne@68
|
4534 The size, in bytes, of a complete pixel; 1 for a color-mapped image.
|
|
jpayne@68
|
4535
|
|
jpayne@68
|
4536 Information about the whole row, or whole image
|
|
jpayne@68
|
4537
|
|
jpayne@68
|
4538 PNG_IMAGE_ROW_STRIDE(image)
|
|
jpayne@68
|
4539 Returns the total number of components in a single row of the image; this
|
|
jpayne@68
|
4540 is the minimum 'row stride', the minimum count of components between each
|
|
jpayne@68
|
4541 row. For a color-mapped image this is the minimum number of bytes in a
|
|
jpayne@68
|
4542 row.
|
|
jpayne@68
|
4543
|
|
jpayne@68
|
4544 If you need the stride measured in bytes, row_stride_bytes is
|
|
jpayne@68
|
4545 PNG_IMAGE_ROW_STRIDE(image) * PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt)
|
|
jpayne@68
|
4546 plus any padding bytes that your application might need, for example
|
|
jpayne@68
|
4547 to start the next row on a 4-byte boundary.
|
|
jpayne@68
|
4548
|
|
jpayne@68
|
4549 PNG_IMAGE_BUFFER_SIZE(image, row_stride)
|
|
jpayne@68
|
4550 Return the size, in bytes, of an image buffer given a png_image and a row
|
|
jpayne@68
|
4551 stride - the number of components to leave space for in each row.
|
|
jpayne@68
|
4552
|
|
jpayne@68
|
4553 PNG_IMAGE_SIZE(image)
|
|
jpayne@68
|
4554 Return the size, in bytes, of the image in memory given just a png_image;
|
|
jpayne@68
|
4555 the row stride is the minimum stride required for the image.
|
|
jpayne@68
|
4556
|
|
jpayne@68
|
4557 PNG_IMAGE_COLORMAP_SIZE(image)
|
|
jpayne@68
|
4558 Return the size, in bytes, of the color-map of this image. If the image
|
|
jpayne@68
|
4559 format is not a color-map format this will return a size sufficient for
|
|
jpayne@68
|
4560 256 entries in the given format; check PNG_FORMAT_FLAG_COLORMAP if
|
|
jpayne@68
|
4561 you don't want to allocate a color-map in this case.
|
|
jpayne@68
|
4562
|
|
jpayne@68
|
4563 PNG_IMAGE_FLAG_*
|
|
jpayne@68
|
4564
|
|
jpayne@68
|
4565 Flags containing additional information about the image are held in
|
|
jpayne@68
|
4566 the 'flags' field of png_image.
|
|
jpayne@68
|
4567
|
|
jpayne@68
|
4568 PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB == 0x01
|
|
jpayne@68
|
4569 This indicates that the RGB values of the in-memory bitmap do not
|
|
jpayne@68
|
4570 correspond to the red, green and blue end-points defined by sRGB.
|
|
jpayne@68
|
4571
|
|
jpayne@68
|
4572 PNG_IMAGE_FLAG_FAST == 0x02
|
|
jpayne@68
|
4573 On write emphasise speed over compression; the resultant PNG file will be
|
|
jpayne@68
|
4574 larger but will be produced significantly faster, particular for large
|
|
jpayne@68
|
4575 images. Do not use this option for images which will be distributed, only
|
|
jpayne@68
|
4576 used it when producing intermediate files that will be read back in
|
|
jpayne@68
|
4577 repeatedly. For a typical 24-bit image the option will double the read
|
|
jpayne@68
|
4578 speed at the cost of increasing the image size by 25%, however for many
|
|
jpayne@68
|
4579 more compressible images the PNG file can be 10 times larger with only a
|
|
jpayne@68
|
4580 slight speed gain.
|
|
jpayne@68
|
4581
|
|
jpayne@68
|
4582 PNG_IMAGE_FLAG_16BIT_sRGB == 0x04
|
|
jpayne@68
|
4583 On read if the image is a 16-bit per component image and there is no gAMA
|
|
jpayne@68
|
4584 or sRGB chunk assume that the components are sRGB encoded. Notice that
|
|
jpayne@68
|
4585 images output by the simplified API always have gamma information; setting
|
|
jpayne@68
|
4586 this flag only affects the interpretation of 16-bit images from an
|
|
jpayne@68
|
4587 external source. It is recommended that the application expose this flag
|
|
jpayne@68
|
4588 to the user; the user can normally easily recognize the difference between
|
|
jpayne@68
|
4589 linear and sRGB encoding. This flag has no effect on write - the data
|
|
jpayne@68
|
4590 passed to the write APIs must have the correct encoding (as defined
|
|
jpayne@68
|
4591 above.)
|
|
jpayne@68
|
4592
|
|
jpayne@68
|
4593 If the flag is not set (the default) input 16-bit per component data is
|
|
jpayne@68
|
4594 assumed to be linear.
|
|
jpayne@68
|
4595
|
|
jpayne@68
|
4596 NOTE: the flag can only be set after the png_image_begin_read_ call,
|
|
jpayne@68
|
4597 because that call initializes the 'flags' field.
|
|
jpayne@68
|
4598
|
|
jpayne@68
|
4599 READ APIs
|
|
jpayne@68
|
4600
|
|
jpayne@68
|
4601 The png_image passed to the read APIs must have been initialized by setting
|
|
jpayne@68
|
4602 the png_controlp field 'opaque' to NULL (or, better, memset the whole thing.)
|
|
jpayne@68
|
4603
|
|
jpayne@68
|
4604 int png_image_begin_read_from_file( png_imagep image,
|
|
jpayne@68
|
4605 const char *file_name)
|
|
jpayne@68
|
4606
|
|
jpayne@68
|
4607 The named file is opened for read and the image header
|
|
jpayne@68
|
4608 is filled in from the PNG header in the file.
|
|
jpayne@68
|
4609
|
|
jpayne@68
|
4610 int png_image_begin_read_from_stdio (png_imagep image,
|
|
jpayne@68
|
4611 FILE* file)
|
|
jpayne@68
|
4612
|
|
jpayne@68
|
4613 The PNG header is read from the stdio FILE object.
|
|
jpayne@68
|
4614
|
|
jpayne@68
|
4615 int png_image_begin_read_from_memory(png_imagep image,
|
|
jpayne@68
|
4616 png_const_voidp memory, size_t size)
|
|
jpayne@68
|
4617
|
|
jpayne@68
|
4618 The PNG header is read from the given memory buffer.
|
|
jpayne@68
|
4619
|
|
jpayne@68
|
4620 int png_image_finish_read(png_imagep image,
|
|
jpayne@68
|
4621 png_colorp background, void *buffer,
|
|
jpayne@68
|
4622 png_int_32 row_stride, void *colormap));
|
|
jpayne@68
|
4623
|
|
jpayne@68
|
4624 Finish reading the image into the supplied buffer and
|
|
jpayne@68
|
4625 clean up the png_image structure.
|
|
jpayne@68
|
4626
|
|
jpayne@68
|
4627 row_stride is the step, in png_byte or png_uint_16 units
|
|
jpayne@68
|
4628 as appropriate, between adjacent rows. A positive stride
|
|
jpayne@68
|
4629 indicates that the top-most row is first in the buffer -
|
|
jpayne@68
|
4630 the normal top-down arrangement. A negative stride
|
|
jpayne@68
|
4631 indicates that the bottom-most row is first in the buffer.
|
|
jpayne@68
|
4632
|
|
jpayne@68
|
4633 background need only be supplied if an alpha channel must
|
|
jpayne@68
|
4634 be removed from a png_byte format and the removal is to be
|
|
jpayne@68
|
4635 done by compositing on a solid color; otherwise it may be
|
|
jpayne@68
|
4636 NULL and any composition will be done directly onto the
|
|
jpayne@68
|
4637 buffer. The value is an sRGB color to use for the
|
|
jpayne@68
|
4638 background, for grayscale output the green channel is used.
|
|
jpayne@68
|
4639
|
|
jpayne@68
|
4640 For linear output removing the alpha channel is always done
|
|
jpayne@68
|
4641 by compositing on black.
|
|
jpayne@68
|
4642
|
|
jpayne@68
|
4643 void png_image_free(png_imagep image)
|
|
jpayne@68
|
4644
|
|
jpayne@68
|
4645 Free any data allocated by libpng in image->opaque,
|
|
jpayne@68
|
4646 setting the pointer to NULL. May be called at any time
|
|
jpayne@68
|
4647 after the structure is initialized.
|
|
jpayne@68
|
4648
|
|
jpayne@68
|
4649 When the simplified API needs to convert between sRGB and linear colorspaces,
|
|
jpayne@68
|
4650 the actual sRGB transfer curve defined in the sRGB specification (see the
|
|
jpayne@68
|
4651 article at https://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2
|
|
jpayne@68
|
4652 approximation used elsewhere in libpng.
|
|
jpayne@68
|
4653
|
|
jpayne@68
|
4654 WRITE APIS
|
|
jpayne@68
|
4655
|
|
jpayne@68
|
4656 For write you must initialize a png_image structure to describe the image to
|
|
jpayne@68
|
4657 be written:
|
|
jpayne@68
|
4658
|
|
jpayne@68
|
4659 version: must be set to PNG_IMAGE_VERSION
|
|
jpayne@68
|
4660 opaque: must be initialized to NULL
|
|
jpayne@68
|
4661 width: image width in pixels
|
|
jpayne@68
|
4662 height: image height in rows
|
|
jpayne@68
|
4663 format: the format of the data you wish to write
|
|
jpayne@68
|
4664 flags: set to 0 unless one of the defined flags applies; set
|
|
jpayne@68
|
4665 PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB for color format images
|
|
jpayne@68
|
4666 where the RGB values do not correspond to the colors in sRGB.
|
|
jpayne@68
|
4667 colormap_entries: set to the number of entries in the color-map (0 to 256)
|
|
jpayne@68
|
4668
|
|
jpayne@68
|
4669 int png_image_write_to_file, (png_imagep image,
|
|
jpayne@68
|
4670 const char *file, int convert_to_8bit, const void *buffer,
|
|
jpayne@68
|
4671 png_int_32 row_stride, const void *colormap));
|
|
jpayne@68
|
4672
|
|
jpayne@68
|
4673 Write the image to the named file.
|
|
jpayne@68
|
4674
|
|
jpayne@68
|
4675 int png_image_write_to_memory (png_imagep image, void *memory,
|
|
jpayne@68
|
4676 png_alloc_size_t * PNG_RESTRICT memory_bytes,
|
|
jpayne@68
|
4677 int convert_to_8_bit, const void *buffer, ptrdiff_t row_stride,
|
|
jpayne@68
|
4678 const void *colormap));
|
|
jpayne@68
|
4679
|
|
jpayne@68
|
4680 Write the image to memory.
|
|
jpayne@68
|
4681
|
|
jpayne@68
|
4682 int png_image_write_to_stdio(png_imagep image, FILE *file,
|
|
jpayne@68
|
4683 int convert_to_8_bit, const void *buffer,
|
|
jpayne@68
|
4684 png_int_32 row_stride, const void *colormap)
|
|
jpayne@68
|
4685
|
|
jpayne@68
|
4686 Write the image to the given (FILE*).
|
|
jpayne@68
|
4687
|
|
jpayne@68
|
4688 With all write APIs if image is in one of the linear formats with
|
|
jpayne@68
|
4689 (png_uint_16) data then setting convert_to_8_bit will cause the output to be
|
|
jpayne@68
|
4690 a (png_byte) PNG gamma encoded according to the sRGB specification, otherwise
|
|
jpayne@68
|
4691 a 16-bit linear encoded PNG file is written.
|
|
jpayne@68
|
4692
|
|
jpayne@68
|
4693 With all APIs row_stride is handled as in the read APIs - it is the spacing
|
|
jpayne@68
|
4694 from one row to the next in component sized units (float) and if negative
|
|
jpayne@68
|
4695 indicates a bottom-up row layout in the buffer. If you pass zero, libpng will
|
|
jpayne@68
|
4696 calculate the row_stride for you from the width and number of channels.
|
|
jpayne@68
|
4697
|
|
jpayne@68
|
4698 Note that the write API does not support interlacing, sub-8-bit pixels,
|
|
jpayne@68
|
4699 indexed (paletted) images, or most ancillary chunks.
|
|
jpayne@68
|
4700
|
|
jpayne@68
|
4701 .SH VI. Modifying/Customizing libpng
|
|
jpayne@68
|
4702
|
|
jpayne@68
|
4703 There are two issues here. The first is changing how libpng does
|
|
jpayne@68
|
4704 standard things like memory allocation, input/output, and error handling.
|
|
jpayne@68
|
4705 The second deals with more complicated things like adding new chunks,
|
|
jpayne@68
|
4706 adding new transformations, and generally changing how libpng works.
|
|
jpayne@68
|
4707 Both of those are compile-time issues; that is, they are generally
|
|
jpayne@68
|
4708 determined at the time the code is written, and there is rarely a need
|
|
jpayne@68
|
4709 to provide the user with a means of changing them.
|
|
jpayne@68
|
4710
|
|
jpayne@68
|
4711 Memory allocation, input/output, and error handling
|
|
jpayne@68
|
4712
|
|
jpayne@68
|
4713 All of the memory allocation, input/output, and error handling in libpng
|
|
jpayne@68
|
4714 goes through callbacks that are user-settable. The default routines are
|
|
jpayne@68
|
4715 in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
|
|
jpayne@68
|
4716 these functions, call the appropriate png_set_*_fn() function.
|
|
jpayne@68
|
4717
|
|
jpayne@68
|
4718 Memory allocation is done through the functions png_malloc(), png_calloc(),
|
|
jpayne@68
|
4719 and png_free(). The png_malloc() and png_free() functions currently just
|
|
jpayne@68
|
4720 call the standard C functions and png_calloc() calls png_malloc() and then
|
|
jpayne@68
|
4721 clears the newly allocated memory to zero; note that png_calloc(png_ptr, size)
|
|
jpayne@68
|
4722 is not the same as the calloc(number, size) function provided by stdlib.h.
|
|
jpayne@68
|
4723 There is limited support for certain systems with segmented memory
|
|
jpayne@68
|
4724 architectures and the types of pointers declared by png.h match this; you
|
|
jpayne@68
|
4725 will have to use appropriate pointers in your application. If you prefer
|
|
jpayne@68
|
4726 to use a different method of allocating and freeing data, you can use
|
|
jpayne@68
|
4727 png_create_read_struct_2() or png_create_write_struct_2() to register your
|
|
jpayne@68
|
4728 own functions as described above. These functions also provide a void
|
|
jpayne@68
|
4729 pointer that can be retrieved via
|
|
jpayne@68
|
4730
|
|
jpayne@68
|
4731 mem_ptr = png_get_mem_ptr(png_ptr);
|
|
jpayne@68
|
4732
|
|
jpayne@68
|
4733 Your replacement memory functions must have prototypes as follows:
|
|
jpayne@68
|
4734
|
|
jpayne@68
|
4735 png_voidp malloc_fn(png_structp png_ptr,
|
|
jpayne@68
|
4736 png_alloc_size_t size);
|
|
jpayne@68
|
4737
|
|
jpayne@68
|
4738 void free_fn(png_structp png_ptr, png_voidp ptr);
|
|
jpayne@68
|
4739
|
|
jpayne@68
|
4740 Your malloc_fn() must return NULL in case of failure. The png_malloc()
|
|
jpayne@68
|
4741 function will normally call png_error() if it receives a NULL from the
|
|
jpayne@68
|
4742 system memory allocator or from your replacement malloc_fn().
|
|
jpayne@68
|
4743
|
|
jpayne@68
|
4744 Your free_fn() will never be called with a NULL ptr, since libpng's
|
|
jpayne@68
|
4745 png_free() checks for NULL before calling free_fn().
|
|
jpayne@68
|
4746
|
|
jpayne@68
|
4747 Input/Output in libpng is done through png_read() and png_write(),
|
|
jpayne@68
|
4748 which currently just call fread() and fwrite(). The FILE * is stored in
|
|
jpayne@68
|
4749 png_struct and is initialized via png_init_io(). If you wish to change
|
|
jpayne@68
|
4750 the method of I/O, the library supplies callbacks that you can set
|
|
jpayne@68
|
4751 through the function png_set_read_fn() and png_set_write_fn() at run
|
|
jpayne@68
|
4752 time, instead of calling the png_init_io() function. These functions
|
|
jpayne@68
|
4753 also provide a void pointer that can be retrieved via the function
|
|
jpayne@68
|
4754 png_get_io_ptr(). For example:
|
|
jpayne@68
|
4755
|
|
jpayne@68
|
4756 png_set_read_fn(png_structp read_ptr,
|
|
jpayne@68
|
4757 voidp read_io_ptr, png_rw_ptr read_data_fn)
|
|
jpayne@68
|
4758
|
|
jpayne@68
|
4759 png_set_write_fn(png_structp write_ptr,
|
|
jpayne@68
|
4760 voidp write_io_ptr, png_rw_ptr write_data_fn,
|
|
jpayne@68
|
4761 png_flush_ptr output_flush_fn);
|
|
jpayne@68
|
4762
|
|
jpayne@68
|
4763 voidp read_io_ptr = png_get_io_ptr(read_ptr);
|
|
jpayne@68
|
4764 voidp write_io_ptr = png_get_io_ptr(write_ptr);
|
|
jpayne@68
|
4765
|
|
jpayne@68
|
4766 The replacement I/O functions must have prototypes as follows:
|
|
jpayne@68
|
4767
|
|
jpayne@68
|
4768 void user_read_data(png_structp png_ptr,
|
|
jpayne@68
|
4769 png_bytep data, size_t length);
|
|
jpayne@68
|
4770
|
|
jpayne@68
|
4771 void user_write_data(png_structp png_ptr,
|
|
jpayne@68
|
4772 png_bytep data, size_t length);
|
|
jpayne@68
|
4773
|
|
jpayne@68
|
4774 void user_flush_data(png_structp png_ptr);
|
|
jpayne@68
|
4775
|
|
jpayne@68
|
4776 The user_read_data() function is responsible for detecting and
|
|
jpayne@68
|
4777 handling end-of-data errors.
|
|
jpayne@68
|
4778
|
|
jpayne@68
|
4779 Supplying NULL for the read, write, or flush functions sets them back
|
|
jpayne@68
|
4780 to using the default C stream functions, which expect the io_ptr to
|
|
jpayne@68
|
4781 point to a standard *FILE structure. It is probably a mistake
|
|
jpayne@68
|
4782 to use NULL for one of write_data_fn and output_flush_fn but not both
|
|
jpayne@68
|
4783 of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
|
|
jpayne@68
|
4784 It is an error to read from a write stream, and vice versa.
|
|
jpayne@68
|
4785
|
|
jpayne@68
|
4786 Error handling in libpng is done through png_error() and png_warning().
|
|
jpayne@68
|
4787 Errors handled through png_error() are fatal, meaning that png_error()
|
|
jpayne@68
|
4788 should never return to its caller. Currently, this is handled via
|
|
jpayne@68
|
4789 setjmp() and longjmp() (unless you have compiled libpng with
|
|
jpayne@68
|
4790 PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()),
|
|
jpayne@68
|
4791 but you could change this to do things like exit() if you should wish,
|
|
jpayne@68
|
4792 as long as your function does not return.
|
|
jpayne@68
|
4793
|
|
jpayne@68
|
4794 On non-fatal errors, png_warning() is called
|
|
jpayne@68
|
4795 to print a warning message, and then control returns to the calling code.
|
|
jpayne@68
|
4796 By default png_error() and png_warning() print a message on stderr via
|
|
jpayne@68
|
4797 fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
|
|
jpayne@68
|
4798 (because you don't want the messages) or PNG_NO_STDIO defined (because
|
|
jpayne@68
|
4799 fprintf() isn't available). If you wish to change the behavior of the error
|
|
jpayne@68
|
4800 functions, you will need to set up your own message callbacks. These
|
|
jpayne@68
|
4801 functions are normally supplied at the time that the png_struct is created.
|
|
jpayne@68
|
4802 It is also possible to redirect errors and warnings to your own replacement
|
|
jpayne@68
|
4803 functions after png_create_*_struct() has been called by calling:
|
|
jpayne@68
|
4804
|
|
jpayne@68
|
4805 png_set_error_fn(png_structp png_ptr,
|
|
jpayne@68
|
4806 png_voidp error_ptr, png_error_ptr error_fn,
|
|
jpayne@68
|
4807 png_error_ptr warning_fn);
|
|
jpayne@68
|
4808
|
|
jpayne@68
|
4809 If NULL is supplied for either error_fn or warning_fn, then the libpng
|
|
jpayne@68
|
4810 default function will be used, calling fprintf() and/or longjmp() if a
|
|
jpayne@68
|
4811 problem is encountered. The replacement error functions should have
|
|
jpayne@68
|
4812 parameters as follows:
|
|
jpayne@68
|
4813
|
|
jpayne@68
|
4814 void user_error_fn(png_structp png_ptr,
|
|
jpayne@68
|
4815 png_const_charp error_msg);
|
|
jpayne@68
|
4816
|
|
jpayne@68
|
4817 void user_warning_fn(png_structp png_ptr,
|
|
jpayne@68
|
4818 png_const_charp warning_msg);
|
|
jpayne@68
|
4819
|
|
jpayne@68
|
4820 Then, within your user_error_fn or user_warning_fn, you can retrieve
|
|
jpayne@68
|
4821 the error_ptr if you need it, by calling
|
|
jpayne@68
|
4822
|
|
jpayne@68
|
4823 png_voidp error_ptr = png_get_error_ptr(png_ptr);
|
|
jpayne@68
|
4824
|
|
jpayne@68
|
4825 The motivation behind using setjmp() and longjmp() is the C++ throw and
|
|
jpayne@68
|
4826 catch exception handling methods. This makes the code much easier to write,
|
|
jpayne@68
|
4827 as there is no need to check every return code of every function call.
|
|
jpayne@68
|
4828 However, there are some uncertainties about the status of local variables
|
|
jpayne@68
|
4829 after a longjmp, so the user may want to be careful about doing anything
|
|
jpayne@68
|
4830 after setjmp returns non-zero besides returning itself. Consult your
|
|
jpayne@68
|
4831 compiler documentation for more details. For an alternative approach, you
|
|
jpayne@68
|
4832 may wish to use the "cexcept" facility (see https://cexcept.sourceforge.io/),
|
|
jpayne@68
|
4833 which is illustrated in pngvalid.c and in contrib/visupng.
|
|
jpayne@68
|
4834
|
|
jpayne@68
|
4835 Beginning in libpng-1.4.0, the png_set_benign_errors() API became available.
|
|
jpayne@68
|
4836 You can use this to handle certain errors (normally handled as errors)
|
|
jpayne@68
|
4837 as warnings.
|
|
jpayne@68
|
4838
|
|
jpayne@68
|
4839 png_set_benign_errors (png_ptr, int allowed);
|
|
jpayne@68
|
4840
|
|
jpayne@68
|
4841 allowed: 0: treat png_benign_error() as an error.
|
|
jpayne@68
|
4842 1: treat png_benign_error() as a warning.
|
|
jpayne@68
|
4843
|
|
jpayne@68
|
4844 As of libpng-1.6.0, the default condition is to treat benign errors as
|
|
jpayne@68
|
4845 warnings while reading and as errors while writing.
|
|
jpayne@68
|
4846
|
|
jpayne@68
|
4847 .SS Custom chunks
|
|
jpayne@68
|
4848
|
|
jpayne@68
|
4849 If you need to read or write custom chunks, you may need to get deeper
|
|
jpayne@68
|
4850 into the libpng code. The library now has mechanisms for storing
|
|
jpayne@68
|
4851 and writing chunks of unknown type; you can even declare callbacks
|
|
jpayne@68
|
4852 for custom chunks. However, this may not be good enough if the
|
|
jpayne@68
|
4853 library code itself needs to know about interactions between your
|
|
jpayne@68
|
4854 chunk and existing `intrinsic' chunks.
|
|
jpayne@68
|
4855
|
|
jpayne@68
|
4856 If you need to write a new intrinsic chunk, first read the PNG
|
|
jpayne@68
|
4857 specification. Acquire a first level of understanding of how it works.
|
|
jpayne@68
|
4858 Pay particular attention to the sections that describe chunk names,
|
|
jpayne@68
|
4859 and look at how other chunks were designed, so you can do things
|
|
jpayne@68
|
4860 similarly. Second, check out the sections of libpng that read and
|
|
jpayne@68
|
4861 write chunks. Try to find a chunk that is similar to yours and use
|
|
jpayne@68
|
4862 it as a template. More details can be found in the comments inside
|
|
jpayne@68
|
4863 the code. It is best to handle private or unknown chunks in a generic method,
|
|
jpayne@68
|
4864 via callback functions, instead of by modifying libpng functions. This
|
|
jpayne@68
|
4865 is illustrated in pngtest.c, which uses a callback function to handle a
|
|
jpayne@68
|
4866 private "vpAg" chunk and the new "sTER" chunk, which are both unknown to
|
|
jpayne@68
|
4867 libpng.
|
|
jpayne@68
|
4868
|
|
jpayne@68
|
4869 If you wish to write your own transformation for the data, look through
|
|
jpayne@68
|
4870 the part of the code that does the transformations, and check out some of
|
|
jpayne@68
|
4871 the simpler ones to get an idea of how they work. Try to find a similar
|
|
jpayne@68
|
4872 transformation to the one you want to add and copy off of it. More details
|
|
jpayne@68
|
4873 can be found in the comments inside the code itself.
|
|
jpayne@68
|
4874
|
|
jpayne@68
|
4875 .SS Configuring for gui/windowing platforms:
|
|
jpayne@68
|
4876
|
|
jpayne@68
|
4877 You will need to write new error and warning functions that use the GUI
|
|
jpayne@68
|
4878 interface, as described previously, and set them to be the error and
|
|
jpayne@68
|
4879 warning functions at the time that png_create_*_struct() is called,
|
|
jpayne@68
|
4880 in order to have them available during the structure initialization.
|
|
jpayne@68
|
4881 They can be changed later via png_set_error_fn(). On some compilers,
|
|
jpayne@68
|
4882 you may also have to change the memory allocators (png_malloc, etc.).
|
|
jpayne@68
|
4883
|
|
jpayne@68
|
4884 .SS Configuring zlib:
|
|
jpayne@68
|
4885
|
|
jpayne@68
|
4886 There are special functions to configure the compression. Perhaps the
|
|
jpayne@68
|
4887 most useful one changes the compression level, which currently uses
|
|
jpayne@68
|
4888 input compression values in the range 0 - 9. The library normally
|
|
jpayne@68
|
4889 uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
|
|
jpayne@68
|
4890 have shown that for a large majority of images, compression values in
|
|
jpayne@68
|
4891 the range 3-6 compress nearly as well as higher levels, and do so much
|
|
jpayne@68
|
4892 faster. For online applications it may be desirable to have maximum speed
|
|
jpayne@68
|
4893 (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
|
|
jpayne@68
|
4894 specify no compression (Z_NO_COMPRESSION = 0), but this would create
|
|
jpayne@68
|
4895 files larger than just storing the raw bitmap. You can specify the
|
|
jpayne@68
|
4896 compression level by calling:
|
|
jpayne@68
|
4897
|
|
jpayne@68
|
4898 #include zlib.h
|
|
jpayne@68
|
4899 png_set_compression_level(png_ptr, level);
|
|
jpayne@68
|
4900
|
|
jpayne@68
|
4901 Another useful one is to reduce the memory level used by the library.
|
|
jpayne@68
|
4902 The memory level defaults to 8, but it can be lowered if you are
|
|
jpayne@68
|
4903 short on memory (running DOS, for example, where you only have 640K).
|
|
jpayne@68
|
4904 Note that the memory level does have an effect on compression; among
|
|
jpayne@68
|
4905 other things, lower levels will result in sections of incompressible
|
|
jpayne@68
|
4906 data being emitted in smaller stored blocks, with a correspondingly
|
|
jpayne@68
|
4907 larger relative overhead of up to 15% in the worst case.
|
|
jpayne@68
|
4908
|
|
jpayne@68
|
4909 #include zlib.h
|
|
jpayne@68
|
4910 png_set_compression_mem_level(png_ptr, level);
|
|
jpayne@68
|
4911
|
|
jpayne@68
|
4912 The other functions are for configuring zlib. They are not recommended
|
|
jpayne@68
|
4913 for normal use and may result in writing an invalid PNG file. See
|
|
jpayne@68
|
4914 zlib.h for more information on what these mean.
|
|
jpayne@68
|
4915
|
|
jpayne@68
|
4916 #include zlib.h
|
|
jpayne@68
|
4917 png_set_compression_strategy(png_ptr,
|
|
jpayne@68
|
4918 strategy);
|
|
jpayne@68
|
4919
|
|
jpayne@68
|
4920 png_set_compression_window_bits(png_ptr,
|
|
jpayne@68
|
4921 window_bits);
|
|
jpayne@68
|
4922
|
|
jpayne@68
|
4923 png_set_compression_method(png_ptr, method);
|
|
jpayne@68
|
4924
|
|
jpayne@68
|
4925 This controls the size of the IDAT chunks (default 8192):
|
|
jpayne@68
|
4926
|
|
jpayne@68
|
4927 png_set_compression_buffer_size(png_ptr, size);
|
|
jpayne@68
|
4928
|
|
jpayne@68
|
4929 As of libpng version 1.5.4, additional APIs became
|
|
jpayne@68
|
4930 available to set these separately for non-IDAT
|
|
jpayne@68
|
4931 compressed chunks such as zTXt, iTXt, and iCCP:
|
|
jpayne@68
|
4932
|
|
jpayne@68
|
4933 #include zlib.h
|
|
jpayne@68
|
4934 #if PNG_LIBPNG_VER >= 10504
|
|
jpayne@68
|
4935 png_set_text_compression_level(png_ptr, level);
|
|
jpayne@68
|
4936
|
|
jpayne@68
|
4937 png_set_text_compression_mem_level(png_ptr, level);
|
|
jpayne@68
|
4938
|
|
jpayne@68
|
4939 png_set_text_compression_strategy(png_ptr,
|
|
jpayne@68
|
4940 strategy);
|
|
jpayne@68
|
4941
|
|
jpayne@68
|
4942 png_set_text_compression_window_bits(png_ptr,
|
|
jpayne@68
|
4943 window_bits);
|
|
jpayne@68
|
4944
|
|
jpayne@68
|
4945 png_set_text_compression_method(png_ptr, method);
|
|
jpayne@68
|
4946 #endif
|
|
jpayne@68
|
4947
|
|
jpayne@68
|
4948 .SS Controlling row filtering
|
|
jpayne@68
|
4949
|
|
jpayne@68
|
4950 If you want to control whether libpng uses filtering or not, which
|
|
jpayne@68
|
4951 filters are used, and how it goes about picking row filters, you
|
|
jpayne@68
|
4952 can call one of these functions. The selection and configuration
|
|
jpayne@68
|
4953 of row filters can have a significant impact on the size and
|
|
jpayne@68
|
4954 encoding speed and a somewhat lesser impact on the decoding speed
|
|
jpayne@68
|
4955 of an image. Filtering is enabled by default for RGB and grayscale
|
|
jpayne@68
|
4956 images (with and without alpha), but not for paletted images nor
|
|
jpayne@68
|
4957 for any images with bit depths less than 8 bits/pixel.
|
|
jpayne@68
|
4958
|
|
jpayne@68
|
4959 The 'method' parameter sets the main filtering method, which is
|
|
jpayne@68
|
4960 currently only '0' in the PNG 1.2 specification. The 'filters'
|
|
jpayne@68
|
4961 parameter sets which filter(s), if any, should be used for each
|
|
jpayne@68
|
4962 scanline. Possible values are PNG_ALL_FILTERS, PNG_NO_FILTERS,
|
|
jpayne@68
|
4963 or PNG_FAST_FILTERS to turn filtering on and off, or to turn on
|
|
jpayne@68
|
4964 just the fast-decoding subset of filters, respectively.
|
|
jpayne@68
|
4965
|
|
jpayne@68
|
4966 Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
|
|
jpayne@68
|
4967 PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
|
|
jpayne@68
|
4968 ORed together with '|' to specify one or more filters to use.
|
|
jpayne@68
|
4969 These filters are described in more detail in the PNG specification.
|
|
jpayne@68
|
4970 If you intend to change the filter type during the course of writing
|
|
jpayne@68
|
4971 the image, you should start with flags set for all of the filters
|
|
jpayne@68
|
4972 you intend to use so that libpng can initialize its internal
|
|
jpayne@68
|
4973 structures appropriately for all of the filter types. (Note that this
|
|
jpayne@68
|
4974 means the first row must always be adaptively filtered, because libpng
|
|
jpayne@68
|
4975 currently does not allocate the filter buffers until png_write_row()
|
|
jpayne@68
|
4976 is called for the first time.)
|
|
jpayne@68
|
4977
|
|
jpayne@68
|
4978 filters = PNG_NO_FILTERS;
|
|
jpayne@68
|
4979 filters = PNG_ALL_FILTERS;
|
|
jpayne@68
|
4980 filters = PNG_FAST_FILTERS;
|
|
jpayne@68
|
4981
|
|
jpayne@68
|
4982 or
|
|
jpayne@68
|
4983
|
|
jpayne@68
|
4984 filters = PNG_FILTER_NONE | PNG_FILTER_SUB |
|
|
jpayne@68
|
4985 PNG_FILTER_UP | PNG_FILTER_AVG |
|
|
jpayne@68
|
4986 PNG_FILTER_PAETH;
|
|
jpayne@68
|
4987
|
|
jpayne@68
|
4988 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
|
|
jpayne@68
|
4989 filters);
|
|
jpayne@68
|
4990
|
|
jpayne@68
|
4991 The second parameter can also be
|
|
jpayne@68
|
4992 PNG_INTRAPIXEL_DIFFERENCING if you are
|
|
jpayne@68
|
4993 writing a PNG to be embedded in a MNG
|
|
jpayne@68
|
4994 datastream. This parameter must be the
|
|
jpayne@68
|
4995 same as the value of filter_method used
|
|
jpayne@68
|
4996 in png_set_IHDR().
|
|
jpayne@68
|
4997
|
|
jpayne@68
|
4998 .SS Requesting debug printout
|
|
jpayne@68
|
4999
|
|
jpayne@68
|
5000 The macro definition PNG_DEBUG can be used to request debugging
|
|
jpayne@68
|
5001 printout. Set it to an integer value in the range 0 to 3. Higher
|
|
jpayne@68
|
5002 numbers result in increasing amounts of debugging information. The
|
|
jpayne@68
|
5003 information is printed to the "stderr" file, unless another file
|
|
jpayne@68
|
5004 name is specified in the PNG_DEBUG_FILE macro definition.
|
|
jpayne@68
|
5005
|
|
jpayne@68
|
5006 When PNG_DEBUG > 0, the following functions (macros) become available:
|
|
jpayne@68
|
5007
|
|
jpayne@68
|
5008 png_debug(level, message)
|
|
jpayne@68
|
5009 png_debug1(level, message, p1)
|
|
jpayne@68
|
5010 png_debug2(level, message, p1, p2)
|
|
jpayne@68
|
5011
|
|
jpayne@68
|
5012 in which "level" is compared to PNG_DEBUG to decide whether to print
|
|
jpayne@68
|
5013 the message, "message" is the formatted string to be printed,
|
|
jpayne@68
|
5014 and p1 and p2 are parameters that are to be embedded in the string
|
|
jpayne@68
|
5015 according to printf-style formatting directives. For example,
|
|
jpayne@68
|
5016
|
|
jpayne@68
|
5017 png_debug1(2, "foo=%d", foo);
|
|
jpayne@68
|
5018
|
|
jpayne@68
|
5019 is expanded to
|
|
jpayne@68
|
5020
|
|
jpayne@68
|
5021 if (PNG_DEBUG > 2)
|
|
jpayne@68
|
5022 fprintf(PNG_DEBUG_FILE, "foo=%d\en", foo);
|
|
jpayne@68
|
5023
|
|
jpayne@68
|
5024 When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
|
|
jpayne@68
|
5025 can still use PNG_DEBUG to control your own debugging:
|
|
jpayne@68
|
5026
|
|
jpayne@68
|
5027 #ifdef PNG_DEBUG
|
|
jpayne@68
|
5028 fprintf(stderr, ...);
|
|
jpayne@68
|
5029 #endif
|
|
jpayne@68
|
5030
|
|
jpayne@68
|
5031 When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
|
|
jpayne@68
|
5032 having level = 0 will be printed. There aren't any such statements in
|
|
jpayne@68
|
5033 this version of libpng, but if you insert some they will be printed.
|
|
jpayne@68
|
5034
|
|
jpayne@68
|
5035 .SH VII. MNG support
|
|
jpayne@68
|
5036
|
|
jpayne@68
|
5037 The MNG specification (available at http://www.libpng.org/pub/mng) allows
|
|
jpayne@68
|
5038 certain extensions to PNG for PNG images that are embedded in MNG datastreams.
|
|
jpayne@68
|
5039 Libpng can support some of these extensions. To enable them, use the
|
|
jpayne@68
|
5040 png_permit_mng_features() function:
|
|
jpayne@68
|
5041
|
|
jpayne@68
|
5042 feature_set = png_permit_mng_features(png_ptr, mask)
|
|
jpayne@68
|
5043
|
|
jpayne@68
|
5044 mask is a png_uint_32 containing the bitwise OR of the
|
|
jpayne@68
|
5045 features you want to enable. These include
|
|
jpayne@68
|
5046 PNG_FLAG_MNG_EMPTY_PLTE
|
|
jpayne@68
|
5047 PNG_FLAG_MNG_FILTER_64
|
|
jpayne@68
|
5048 PNG_ALL_MNG_FEATURES
|
|
jpayne@68
|
5049
|
|
jpayne@68
|
5050 feature_set is a png_uint_32 that is the bitwise AND of
|
|
jpayne@68
|
5051 your mask with the set of MNG features that is
|
|
jpayne@68
|
5052 supported by the version of libpng that you are using.
|
|
jpayne@68
|
5053
|
|
jpayne@68
|
5054 It is an error to use this function when reading or writing a standalone
|
|
jpayne@68
|
5055 PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
|
|
jpayne@68
|
5056 in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
|
|
jpayne@68
|
5057 and the MHDR and MEND chunks. Libpng does not provide support for these
|
|
jpayne@68
|
5058 or any other MNG chunks; your application must provide its own support for
|
|
jpayne@68
|
5059 them. You may wish to consider using libmng (available at
|
|
jpayne@68
|
5060 https://www.libmng.com/) instead.
|
|
jpayne@68
|
5061
|
|
jpayne@68
|
5062 .SH VIII. Changes to Libpng from version 0.88
|
|
jpayne@68
|
5063
|
|
jpayne@68
|
5064 It should be noted that versions of libpng later than 0.96 are not
|
|
jpayne@68
|
5065 distributed by the original libpng author, Guy Schalnat, nor by
|
|
jpayne@68
|
5066 Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
|
|
jpayne@68
|
5067 distributed versions 0.89 through 0.96, but rather by another member
|
|
jpayne@68
|
5068 of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
|
|
jpayne@68
|
5069 still alive and well, but they have moved on to other things.
|
|
jpayne@68
|
5070
|
|
jpayne@68
|
5071 The old libpng functions png_read_init(), png_write_init(),
|
|
jpayne@68
|
5072 png_info_init(), png_read_destroy(), and png_write_destroy() have been
|
|
jpayne@68
|
5073 moved to PNG_INTERNAL in version 0.95 to discourage their use. These
|
|
jpayne@68
|
5074 functions will be removed from libpng version 1.4.0.
|
|
jpayne@68
|
5075
|
|
jpayne@68
|
5076 The preferred method of creating and initializing the libpng structures is
|
|
jpayne@68
|
5077 via the png_create_read_struct(), png_create_write_struct(), and
|
|
jpayne@68
|
5078 png_create_info_struct() because they isolate the size of the structures
|
|
jpayne@68
|
5079 from the application, allow version error checking, and also allow the
|
|
jpayne@68
|
5080 use of custom error handling routines during the initialization, which
|
|
jpayne@68
|
5081 the old functions do not. The functions png_read_destroy() and
|
|
jpayne@68
|
5082 png_write_destroy() do not actually free the memory that libpng
|
|
jpayne@68
|
5083 allocated for these structs, but just reset the data structures, so they
|
|
jpayne@68
|
5084 can be used instead of png_destroy_read_struct() and
|
|
jpayne@68
|
5085 png_destroy_write_struct() if you feel there is too much system overhead
|
|
jpayne@68
|
5086 allocating and freeing the png_struct for each image read.
|
|
jpayne@68
|
5087
|
|
jpayne@68
|
5088 Setting the error callbacks via png_set_message_fn() before
|
|
jpayne@68
|
5089 png_read_init() as was suggested in libpng-0.88 is no longer supported
|
|
jpayne@68
|
5090 because this caused applications that do not use custom error functions
|
|
jpayne@68
|
5091 to fail if the png_ptr was not initialized to zero. It is still possible
|
|
jpayne@68
|
5092 to set the error callbacks AFTER png_read_init(), or to change them with
|
|
jpayne@68
|
5093 png_set_error_fn(), which is essentially the same function, but with a new
|
|
jpayne@68
|
5094 name to force compilation errors with applications that try to use the old
|
|
jpayne@68
|
5095 method.
|
|
jpayne@68
|
5096
|
|
jpayne@68
|
5097 Support for the sCAL, iCCP, iTXt, and sPLT chunks was added at libpng-1.0.6;
|
|
jpayne@68
|
5098 however, iTXt support was not enabled by default.
|
|
jpayne@68
|
5099
|
|
jpayne@68
|
5100 Starting with version 1.0.7, you can find out which version of the library
|
|
jpayne@68
|
5101 you are using at run-time:
|
|
jpayne@68
|
5102
|
|
jpayne@68
|
5103 png_uint_32 libpng_vn = png_access_version_number();
|
|
jpayne@68
|
5104
|
|
jpayne@68
|
5105 The number libpng_vn is constructed from the major version, minor
|
|
jpayne@68
|
5106 version with leading zero, and release number with leading zero,
|
|
jpayne@68
|
5107 (e.g., libpng_vn for version 1.0.7 is 10007).
|
|
jpayne@68
|
5108
|
|
jpayne@68
|
5109 Note that this function does not take a png_ptr, so you can call it
|
|
jpayne@68
|
5110 before you've created one.
|
|
jpayne@68
|
5111
|
|
jpayne@68
|
5112 You can also check which version of png.h you used when compiling your
|
|
jpayne@68
|
5113 application:
|
|
jpayne@68
|
5114
|
|
jpayne@68
|
5115 png_uint_32 application_vn = PNG_LIBPNG_VER;
|
|
jpayne@68
|
5116
|
|
jpayne@68
|
5117 .SH IX. Changes to Libpng from version 1.0.x to 1.2.x
|
|
jpayne@68
|
5118
|
|
jpayne@68
|
5119 Support for user memory management was enabled by default. To
|
|
jpayne@68
|
5120 accomplish this, the functions png_create_read_struct_2(),
|
|
jpayne@68
|
5121 png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
|
|
jpayne@68
|
5122 png_malloc_default(), and png_free_default() were added.
|
|
jpayne@68
|
5123
|
|
jpayne@68
|
5124 Support for the iTXt chunk has been enabled by default as of
|
|
jpayne@68
|
5125 version 1.2.41.
|
|
jpayne@68
|
5126
|
|
jpayne@68
|
5127 Support for certain MNG features was enabled.
|
|
jpayne@68
|
5128
|
|
jpayne@68
|
5129 Support for numbered error messages was added. However, we never got
|
|
jpayne@68
|
5130 around to actually numbering the error messages. The function
|
|
jpayne@68
|
5131 png_set_strip_error_numbers() was added (Note: the prototype for this
|
|
jpayne@68
|
5132 function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
|
|
jpayne@68
|
5133 builds of libpng-1.2.15. It was restored in libpng-1.2.36).
|
|
jpayne@68
|
5134
|
|
jpayne@68
|
5135 The png_malloc_warn() function was added at libpng-1.2.3. This issues
|
|
jpayne@68
|
5136 a png_warning and returns NULL instead of aborting when it fails to
|
|
jpayne@68
|
5137 acquire the requested memory allocation.
|
|
jpayne@68
|
5138
|
|
jpayne@68
|
5139 Support for setting user limits on image width and height was enabled
|
|
jpayne@68
|
5140 by default. The functions png_set_user_limits(), png_get_user_width_max(),
|
|
jpayne@68
|
5141 and png_get_user_height_max() were added at libpng-1.2.6.
|
|
jpayne@68
|
5142
|
|
jpayne@68
|
5143 The png_set_add_alpha() function was added at libpng-1.2.7.
|
|
jpayne@68
|
5144
|
|
jpayne@68
|
5145 The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
|
|
jpayne@68
|
5146 Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
|
|
jpayne@68
|
5147 tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
|
|
jpayne@68
|
5148 deprecated.
|
|
jpayne@68
|
5149
|
|
jpayne@68
|
5150 A number of macro definitions in support of runtime selection of
|
|
jpayne@68
|
5151 assembler code features (especially Intel MMX code support) were
|
|
jpayne@68
|
5152 added at libpng-1.2.0:
|
|
jpayne@68
|
5153
|
|
jpayne@68
|
5154 PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
|
|
jpayne@68
|
5155 PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
|
|
jpayne@68
|
5156 PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
|
|
jpayne@68
|
5157 PNG_ASM_FLAG_MMX_READ_INTERLACE
|
|
jpayne@68
|
5158 PNG_ASM_FLAG_MMX_READ_FILTER_SUB
|
|
jpayne@68
|
5159 PNG_ASM_FLAG_MMX_READ_FILTER_UP
|
|
jpayne@68
|
5160 PNG_ASM_FLAG_MMX_READ_FILTER_AVG
|
|
jpayne@68
|
5161 PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
|
|
jpayne@68
|
5162 PNG_ASM_FLAGS_INITIALIZED
|
|
jpayne@68
|
5163 PNG_MMX_READ_FLAGS
|
|
jpayne@68
|
5164 PNG_MMX_FLAGS
|
|
jpayne@68
|
5165 PNG_MMX_WRITE_FLAGS
|
|
jpayne@68
|
5166 PNG_MMX_FLAGS
|
|
jpayne@68
|
5167
|
|
jpayne@68
|
5168 We added the following functions in support of runtime
|
|
jpayne@68
|
5169 selection of assembler code features:
|
|
jpayne@68
|
5170
|
|
jpayne@68
|
5171 png_get_mmx_flagmask()
|
|
jpayne@68
|
5172 png_set_mmx_thresholds()
|
|
jpayne@68
|
5173 png_get_asm_flags()
|
|
jpayne@68
|
5174 png_get_mmx_bitdepth_threshold()
|
|
jpayne@68
|
5175 png_get_mmx_rowbytes_threshold()
|
|
jpayne@68
|
5176 png_set_asm_flags()
|
|
jpayne@68
|
5177
|
|
jpayne@68
|
5178 We replaced all of these functions with simple stubs in libpng-1.2.20,
|
|
jpayne@68
|
5179 when the Intel assembler code was removed due to a licensing issue.
|
|
jpayne@68
|
5180
|
|
jpayne@68
|
5181 These macros are deprecated:
|
|
jpayne@68
|
5182
|
|
jpayne@68
|
5183 PNG_READ_TRANSFORMS_NOT_SUPPORTED
|
|
jpayne@68
|
5184 PNG_PROGRESSIVE_READ_NOT_SUPPORTED
|
|
jpayne@68
|
5185 PNG_NO_SEQUENTIAL_READ_SUPPORTED
|
|
jpayne@68
|
5186 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
|
|
jpayne@68
|
5187 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
|
|
jpayne@68
|
5188 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
|
|
jpayne@68
|
5189
|
|
jpayne@68
|
5190 They have been replaced, respectively, by:
|
|
jpayne@68
|
5191
|
|
jpayne@68
|
5192 PNG_NO_READ_TRANSFORMS
|
|
jpayne@68
|
5193 PNG_NO_PROGRESSIVE_READ
|
|
jpayne@68
|
5194 PNG_NO_SEQUENTIAL_READ
|
|
jpayne@68
|
5195 PNG_NO_WRITE_TRANSFORMS
|
|
jpayne@68
|
5196 PNG_NO_READ_ANCILLARY_CHUNKS
|
|
jpayne@68
|
5197 PNG_NO_WRITE_ANCILLARY_CHUNKS
|
|
jpayne@68
|
5198
|
|
jpayne@68
|
5199 PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
|
|
jpayne@68
|
5200 deprecated since libpng-1.0.16 and libpng-1.2.6.
|
|
jpayne@68
|
5201
|
|
jpayne@68
|
5202 The function
|
|
jpayne@68
|
5203 png_check_sig(sig, num)
|
|
jpayne@68
|
5204 was replaced with
|
|
jpayne@68
|
5205 png_sig_cmp(sig, 0, num) == 0
|
|
jpayne@68
|
5206 It has been deprecated since libpng-0.90.
|
|
jpayne@68
|
5207
|
|
jpayne@68
|
5208 The function
|
|
jpayne@68
|
5209 png_set_gray_1_2_4_to_8()
|
|
jpayne@68
|
5210 which also expands tRNS to alpha was replaced with
|
|
jpayne@68
|
5211 png_set_expand_gray_1_2_4_to_8()
|
|
jpayne@68
|
5212 which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
|
|
jpayne@68
|
5213
|
|
jpayne@68
|
5214 .SH X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
|
|
jpayne@68
|
5215
|
|
jpayne@68
|
5216 Private libpng prototypes and macro definitions were moved from
|
|
jpayne@68
|
5217 png.h and pngconf.h into a new pngpriv.h header file.
|
|
jpayne@68
|
5218
|
|
jpayne@68
|
5219 Functions png_set_benign_errors(), png_benign_error(), and
|
|
jpayne@68
|
5220 png_chunk_benign_error() were added.
|
|
jpayne@68
|
5221
|
|
jpayne@68
|
5222 Support for setting the maximum amount of memory that the application
|
|
jpayne@68
|
5223 will allocate for reading chunks was added, as a security measure.
|
|
jpayne@68
|
5224 The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()
|
|
jpayne@68
|
5225 were added to the library.
|
|
jpayne@68
|
5226
|
|
jpayne@68
|
5227 We implemented support for I/O states by adding png_ptr member io_state
|
|
jpayne@68
|
5228 and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
|
|
jpayne@68
|
5229
|
|
jpayne@68
|
5230 We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level
|
|
jpayne@68
|
5231 input transforms.
|
|
jpayne@68
|
5232
|
|
jpayne@68
|
5233 Checking for and reporting of errors in the IHDR chunk is more thorough.
|
|
jpayne@68
|
5234
|
|
jpayne@68
|
5235 Support for global arrays was removed, to improve thread safety.
|
|
jpayne@68
|
5236
|
|
jpayne@68
|
5237 Some obsolete/deprecated macros and functions have been removed.
|
|
jpayne@68
|
5238
|
|
jpayne@68
|
5239 Typecasted NULL definitions such as
|
|
jpayne@68
|
5240 #define png_voidp_NULL (png_voidp)NULL
|
|
jpayne@68
|
5241 were eliminated. If you used these in your application, just use
|
|
jpayne@68
|
5242 NULL instead.
|
|
jpayne@68
|
5243
|
|
jpayne@68
|
5244 The png_struct and info_struct members "trans" and "trans_values" were
|
|
jpayne@68
|
5245 changed to "trans_alpha" and "trans_color", respectively.
|
|
jpayne@68
|
5246
|
|
jpayne@68
|
5247 The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles
|
|
jpayne@68
|
5248 were removed.
|
|
jpayne@68
|
5249
|
|
jpayne@68
|
5250 The PNG_1_0_X and PNG_1_2_X macros were eliminated.
|
|
jpayne@68
|
5251
|
|
jpayne@68
|
5252 The PNG_LEGACY_SUPPORTED macro was eliminated.
|
|
jpayne@68
|
5253
|
|
jpayne@68
|
5254 Many WIN32_WCE #ifdefs were removed.
|
|
jpayne@68
|
5255
|
|
jpayne@68
|
5256 The functions png_read_init(info_ptr), png_write_init(info_ptr),
|
|
jpayne@68
|
5257 png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
|
|
jpayne@68
|
5258 have been removed. They have been deprecated since libpng-0.95.
|
|
jpayne@68
|
5259
|
|
jpayne@68
|
5260 The png_permit_empty_plte() was removed. It has been deprecated
|
|
jpayne@68
|
5261 since libpng-1.0.9. Use png_permit_mng_features() instead.
|
|
jpayne@68
|
5262
|
|
jpayne@68
|
5263 We removed the obsolete stub functions png_get_mmx_flagmask(),
|
|
jpayne@68
|
5264 png_set_mmx_thresholds(), png_get_asm_flags(),
|
|
jpayne@68
|
5265 png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
|
|
jpayne@68
|
5266 png_set_asm_flags(), and png_mmx_supported()
|
|
jpayne@68
|
5267
|
|
jpayne@68
|
5268 We removed the obsolete png_check_sig(), png_memcpy_check(), and
|
|
jpayne@68
|
5269 png_memset_check() functions. Instead use png_sig_cmp() == 0,
|
|
jpayne@68
|
5270 memcpy(), and memset(), respectively.
|
|
jpayne@68
|
5271
|
|
jpayne@68
|
5272 The function png_set_gray_1_2_4_to_8() was removed. It has been
|
|
jpayne@68
|
5273 deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
|
|
jpayne@68
|
5274 png_set_expand_gray_1_2_4_to_8() because the former function also
|
|
jpayne@68
|
5275 expanded any tRNS chunk to an alpha channel.
|
|
jpayne@68
|
5276
|
|
jpayne@68
|
5277 Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32
|
|
jpayne@68
|
5278 were added and are used by default instead of the corresponding
|
|
jpayne@68
|
5279 functions. Unfortunately,
|
|
jpayne@68
|
5280 from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
|
|
jpayne@68
|
5281 function) incorrectly returned a value of type png_uint_32.
|
|
jpayne@68
|
5282
|
|
jpayne@68
|
5283 We changed the prototype for png_malloc() from
|
|
jpayne@68
|
5284 png_malloc(png_structp png_ptr, png_uint_32 size)
|
|
jpayne@68
|
5285 to
|
|
jpayne@68
|
5286 png_malloc(png_structp png_ptr, png_alloc_size_t size)
|
|
jpayne@68
|
5287
|
|
jpayne@68
|
5288 This also applies to the prototype for the user replacement malloc_fn().
|
|
jpayne@68
|
5289
|
|
jpayne@68
|
5290 The png_calloc() function was added and is used in place of
|
|
jpayne@68
|
5291 of "png_malloc(); memset();" except in the case in png_read_png()
|
|
jpayne@68
|
5292 where the array consists of pointers; in this case a "for" loop is used
|
|
jpayne@68
|
5293 after the png_malloc() to set the pointers to NULL, to give robust.
|
|
jpayne@68
|
5294 behavior in case the application runs out of memory part-way through
|
|
jpayne@68
|
5295 the process.
|
|
jpayne@68
|
5296
|
|
jpayne@68
|
5297 We changed the prototypes of png_get_compression_buffer_size() and
|
|
jpayne@68
|
5298 png_set_compression_buffer_size() to work with size_t instead of
|
|
jpayne@68
|
5299 png_uint_32.
|
|
jpayne@68
|
5300
|
|
jpayne@68
|
5301 Support for numbered error messages was removed by default, since we
|
|
jpayne@68
|
5302 never got around to actually numbering the error messages. The function
|
|
jpayne@68
|
5303 png_set_strip_error_numbers() was removed from the library by default.
|
|
jpayne@68
|
5304
|
|
jpayne@68
|
5305 The png_zalloc() and png_zfree() functions are no longer exported.
|
|
jpayne@68
|
5306 The png_zalloc() function no longer zeroes out the memory that it
|
|
jpayne@68
|
5307 allocates. Applications that called png_zalloc(png_ptr, number, size)
|
|
jpayne@68
|
5308 can call png_calloc(png_ptr, number*size) instead, and can call
|
|
jpayne@68
|
5309 png_free() instead of png_zfree().
|
|
jpayne@68
|
5310
|
|
jpayne@68
|
5311 Support for dithering was disabled by default in libpng-1.4.0, because
|
|
jpayne@68
|
5312 it has not been well tested and doesn't actually "dither".
|
|
jpayne@68
|
5313 The code was not
|
|
jpayne@68
|
5314 removed, however, and could be enabled by building libpng with
|
|
jpayne@68
|
5315 PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
|
|
jpayne@68
|
5316 was re-enabled, but the function was renamed png_set_quantize() to
|
|
jpayne@68
|
5317 reflect more accurately what it actually does. At the same time,
|
|
jpayne@68
|
5318 the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
|
|
jpayne@68
|
5319 PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED
|
|
jpayne@68
|
5320 was renamed to PNG_READ_QUANTIZE_SUPPORTED.
|
|
jpayne@68
|
5321
|
|
jpayne@68
|
5322 We removed the trailing '.' from the warning and error messages.
|
|
jpayne@68
|
5323
|
|
jpayne@68
|
5324 .SH XI. Changes to Libpng from version 1.4.x to 1.5.x
|
|
jpayne@68
|
5325
|
|
jpayne@68
|
5326 From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
|
|
jpayne@68
|
5327 function) incorrectly returned a value of type png_uint_32.
|
|
jpayne@68
|
5328 The incorrect macro was removed from libpng-1.4.5.
|
|
jpayne@68
|
5329
|
|
jpayne@68
|
5330 Checking for invalid palette index on write was added at libpng
|
|
jpayne@68
|
5331 1.5.10. If a pixel contains an invalid (out-of-range) index libpng issues
|
|
jpayne@68
|
5332 a benign error. This is enabled by default because this condition is an
|
|
jpayne@68
|
5333 error according to the PNG specification, Clause 11.3.2, but the error can
|
|
jpayne@68
|
5334 be ignored in each png_ptr with
|
|
jpayne@68
|
5335
|
|
jpayne@68
|
5336 png_set_check_for_invalid_index(png_ptr, allowed);
|
|
jpayne@68
|
5337
|
|
jpayne@68
|
5338 allowed - one of
|
|
jpayne@68
|
5339 0: disable benign error (accept the
|
|
jpayne@68
|
5340 invalid data without warning).
|
|
jpayne@68
|
5341 1: enable benign error (treat the
|
|
jpayne@68
|
5342 invalid data as an error or a
|
|
jpayne@68
|
5343 warning).
|
|
jpayne@68
|
5344
|
|
jpayne@68
|
5345 If the error is ignored, or if png_benign_error() treats it as a warning,
|
|
jpayne@68
|
5346 any invalid pixels are decoded as opaque black by the decoder and written
|
|
jpayne@68
|
5347 as-is by the encoder.
|
|
jpayne@68
|
5348
|
|
jpayne@68
|
5349 Retrieving the maximum palette index found was added at libpng-1.5.15.
|
|
jpayne@68
|
5350 This statement must appear after png_read_png() or png_read_image() while
|
|
jpayne@68
|
5351 reading, and after png_write_png() or png_write_image() while writing.
|
|
jpayne@68
|
5352
|
|
jpayne@68
|
5353 int max_palette = png_get_palette_max(png_ptr, info_ptr);
|
|
jpayne@68
|
5354
|
|
jpayne@68
|
5355 This will return the maximum palette index found in the image, or "\-1" if
|
|
jpayne@68
|
5356 the palette was not checked, or "0" if no palette was found. Note that this
|
|
jpayne@68
|
5357 does not account for any palette index used by ancillary chunks such as the
|
|
jpayne@68
|
5358 bKGD chunk; you must check those separately to determine the maximum
|
|
jpayne@68
|
5359 palette index actually used.
|
|
jpayne@68
|
5360
|
|
jpayne@68
|
5361 There are no substantial API changes between the non-deprecated parts of
|
|
jpayne@68
|
5362 the 1.4.5 API and the 1.5.0 API; however, the ability to directly access
|
|
jpayne@68
|
5363 members of the main libpng control structures, png_struct and png_info,
|
|
jpayne@68
|
5364 deprecated in earlier versions of libpng, has been completely removed from
|
|
jpayne@68
|
5365 libpng 1.5, and new private "pngstruct.h", "pnginfo.h", and "pngdebug.h"
|
|
jpayne@68
|
5366 header files were created.
|
|
jpayne@68
|
5367
|
|
jpayne@68
|
5368 We no longer include zlib.h in png.h. The include statement has been moved
|
|
jpayne@68
|
5369 to pngstruct.h, where it is not accessible by applications. Applications that
|
|
jpayne@68
|
5370 need access to information in zlib.h will need to add the '#include "zlib.h"'
|
|
jpayne@68
|
5371 directive. It does not matter whether this is placed prior to or after
|
|
jpayne@68
|
5372 the '"#include png.h"' directive.
|
|
jpayne@68
|
5373
|
|
jpayne@68
|
5374 The png_sprintf(), png_strcpy(), and png_strncpy() macros are no longer used
|
|
jpayne@68
|
5375 and were removed.
|
|
jpayne@68
|
5376
|
|
jpayne@68
|
5377 We moved the png_strlen(), png_memcpy(), png_memset(), and png_memcmp()
|
|
jpayne@68
|
5378 macros into a private header file (pngpriv.h) that is not accessible to
|
|
jpayne@68
|
5379 applications.
|
|
jpayne@68
|
5380
|
|
jpayne@68
|
5381 In png_get_iCCP, the type of "profile" was changed from png_charpp
|
|
jpayne@68
|
5382 to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
|
|
jpayne@68
|
5383
|
|
jpayne@68
|
5384 There are changes of form in png.h, including new and changed macros to
|
|
jpayne@68
|
5385 declare parts of the API. Some API functions with arguments that are
|
|
jpayne@68
|
5386 pointers to data not modified within the function have been corrected to
|
|
jpayne@68
|
5387 declare these arguments with const.
|
|
jpayne@68
|
5388
|
|
jpayne@68
|
5389 Much of the internal use of C macros to control the library build has also
|
|
jpayne@68
|
5390 changed and some of this is visible in the exported header files, in
|
|
jpayne@68
|
5391 particular the use of macros to control data and API elements visible
|
|
jpayne@68
|
5392 during application compilation may require significant revision to
|
|
jpayne@68
|
5393 application code. (It is extremely rare for an application to do this.)
|
|
jpayne@68
|
5394
|
|
jpayne@68
|
5395 Any program that compiled against libpng 1.4 and did not use deprecated
|
|
jpayne@68
|
5396 features or access internal library structures should compile and work
|
|
jpayne@68
|
5397 against libpng 1.5, except for the change in the prototype for
|
|
jpayne@68
|
5398 png_get_iCCP() and png_set_iCCP() API functions mentioned above.
|
|
jpayne@68
|
5399
|
|
jpayne@68
|
5400 libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of
|
|
jpayne@68
|
5401 interlaced images. The macros return the number of rows and columns in
|
|
jpayne@68
|
5402 each pass and information that can be used to de-interlace and (if
|
|
jpayne@68
|
5403 absolutely necessary) interlace an image.
|
|
jpayne@68
|
5404
|
|
jpayne@68
|
5405 libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls
|
|
jpayne@68
|
5406 the application-provided png_longjmp_ptr on the internal, but application
|
|
jpayne@68
|
5407 initialized, longjmp buffer. It is provided as a convenience to avoid
|
|
jpayne@68
|
5408 the need to use the png_jmpbuf macro, which had the unnecessary side
|
|
jpayne@68
|
5409 effect of resetting the internal png_longjmp_ptr value.
|
|
jpayne@68
|
5410
|
|
jpayne@68
|
5411 libpng 1.5.0 includes a complete fixed point API. By default this is
|
|
jpayne@68
|
5412 present along with the corresponding floating point API. In general the
|
|
jpayne@68
|
5413 fixed point API is faster and smaller than the floating point one because
|
|
jpayne@68
|
5414 the PNG file format used fixed point, not floating point. This applies
|
|
jpayne@68
|
5415 even if the library uses floating point in internal calculations. A new
|
|
jpayne@68
|
5416 macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library
|
|
jpayne@68
|
5417 uses floating point arithmetic (the default) or fixed point arithmetic
|
|
jpayne@68
|
5418 internally for performance critical calculations such as gamma correction.
|
|
jpayne@68
|
5419 In some cases, the gamma calculations may produce slightly different
|
|
jpayne@68
|
5420 results. This has changed the results in png_rgb_to_gray and in alpha
|
|
jpayne@68
|
5421 composition (png_set_background for example). This applies even if the
|
|
jpayne@68
|
5422 original image was already linear (gamma == 1.0) and, therefore, it is
|
|
jpayne@68
|
5423 not necessary to linearize the image. This is because libpng has *not*
|
|
jpayne@68
|
5424 been changed to optimize that case correctly, yet.
|
|
jpayne@68
|
5425
|
|
jpayne@68
|
5426 Fixed point support for the sCAL chunk comes with an important caveat;
|
|
jpayne@68
|
5427 the sCAL specification uses a decimal encoding of floating point values
|
|
jpayne@68
|
5428 and the accuracy of PNG fixed point values is insufficient for
|
|
jpayne@68
|
5429 representation of these values. Consequently a "string" API
|
|
jpayne@68
|
5430 (png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading
|
|
jpayne@68
|
5431 arbitrary sCAL chunks in the absence of either the floating point API or
|
|
jpayne@68
|
5432 internal floating point calculations. Starting with libpng-1.5.0, both
|
|
jpayne@68
|
5433 of these functions are present when PNG_sCAL_SUPPORTED is defined. Prior
|
|
jpayne@68
|
5434 to libpng-1.5.0, their presence also depended upon PNG_FIXED_POINT_SUPPORTED
|
|
jpayne@68
|
5435 being defined and PNG_FLOATING_POINT_SUPPORTED not being defined.
|
|
jpayne@68
|
5436
|
|
jpayne@68
|
5437 Applications no longer need to include the optional distribution header
|
|
jpayne@68
|
5438 file pngusr.h or define the corresponding macros during application
|
|
jpayne@68
|
5439 build in order to see the correct variant of the libpng API. From 1.5.0
|
|
jpayne@68
|
5440 application code can check for the corresponding _SUPPORTED macro:
|
|
jpayne@68
|
5441
|
|
jpayne@68
|
5442 #ifdef PNG_INCH_CONVERSIONS_SUPPORTED
|
|
jpayne@68
|
5443 /* code that uses the inch conversion APIs. */
|
|
jpayne@68
|
5444 #endif
|
|
jpayne@68
|
5445
|
|
jpayne@68
|
5446 This macro will only be defined if the inch conversion functions have been
|
|
jpayne@68
|
5447 compiled into libpng. The full set of macros, and whether or not support
|
|
jpayne@68
|
5448 has been compiled in, are available in the header file pnglibconf.h.
|
|
jpayne@68
|
5449 This header file is specific to the libpng build. Notice that prior to
|
|
jpayne@68
|
5450 1.5.0 the _SUPPORTED macros would always have the default definition unless
|
|
jpayne@68
|
5451 reset by pngusr.h or by explicit settings on the compiler command line.
|
|
jpayne@68
|
5452 These settings may produce compiler warnings or errors in 1.5.0 because
|
|
jpayne@68
|
5453 of macro redefinition.
|
|
jpayne@68
|
5454
|
|
jpayne@68
|
5455 Applications can now choose whether to use these macros or to call the
|
|
jpayne@68
|
5456 corresponding function by defining PNG_USE_READ_MACROS or
|
|
jpayne@68
|
5457 PNG_NO_USE_READ_MACROS before including png.h. Notice that this is
|
|
jpayne@68
|
5458 only supported from 1.5.0; defining PNG_NO_USE_READ_MACROS prior to 1.5.0
|
|
jpayne@68
|
5459 will lead to a link failure.
|
|
jpayne@68
|
5460
|
|
jpayne@68
|
5461 Prior to libpng-1.5.4, the zlib compressor used the same set of parameters
|
|
jpayne@68
|
5462 when compressing the IDAT data and textual data such as zTXt and iCCP.
|
|
jpayne@68
|
5463 In libpng-1.5.4 we reinitialized the zlib stream for each type of data.
|
|
jpayne@68
|
5464 We added five png_set_text_*() functions for setting the parameters to
|
|
jpayne@68
|
5465 use with textual data.
|
|
jpayne@68
|
5466
|
|
jpayne@68
|
5467 Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
|
|
jpayne@68
|
5468 option was off by default, and slightly inaccurate scaling occurred.
|
|
jpayne@68
|
5469 This option can no longer be turned off, and the choice of accurate
|
|
jpayne@68
|
5470 or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8()
|
|
jpayne@68
|
5471 API for accurate scaling or the old png_set_strip_16_to_8() API for simple
|
|
jpayne@68
|
5472 chopping. In libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
|
|
jpayne@68
|
5473 macro became PNG_READ_SCALE_16_TO_8_SUPPORTED, and the PNG_READ_16_TO_8
|
|
jpayne@68
|
5474 macro became PNG_READ_STRIP_16_TO_8_SUPPORTED, to enable the two
|
|
jpayne@68
|
5475 png_set_*_16_to_8() functions separately.
|
|
jpayne@68
|
5476
|
|
jpayne@68
|
5477 Prior to libpng-1.5.4, the png_set_user_limits() function could only be
|
|
jpayne@68
|
5478 used to reduce the width and height limits from the value of
|
|
jpayne@68
|
5479 PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said
|
|
jpayne@68
|
5480 that it could be used to override them. Now this function will reduce or
|
|
jpayne@68
|
5481 increase the limits.
|
|
jpayne@68
|
5482
|
|
jpayne@68
|
5483 Starting in libpng-1.5.22, default user limits were established. These
|
|
jpayne@68
|
5484 can be overridden by application calls to png_set_user_limits(),
|
|
jpayne@68
|
5485 png_set_user_chunk_cache_max(), and/or png_set_user_malloc_max().
|
|
jpayne@68
|
5486 The limits are now
|
|
jpayne@68
|
5487 max possible default
|
|
jpayne@68
|
5488 png_user_width_max 0x7fffffff 1,000,000
|
|
jpayne@68
|
5489 png_user_height_max 0x7fffffff 1,000,000
|
|
jpayne@68
|
5490 png_user_chunk_cache_max 0 (unlimited) 1000
|
|
jpayne@68
|
5491 png_user_chunk_malloc_max 0 (unlimited) 8,000,000
|
|
jpayne@68
|
5492
|
|
jpayne@68
|
5493 The png_set_option() function (and the "options" member of the png struct) was
|
|
jpayne@68
|
5494 added to libpng-1.5.15, with option PNG_ARM_NEON.
|
|
jpayne@68
|
5495
|
|
jpayne@68
|
5496 The library now supports a complete fixed point implementation and can
|
|
jpayne@68
|
5497 thus be used on systems that have no floating point support or very
|
|
jpayne@68
|
5498 limited or slow support. Previously gamma correction, an essential part
|
|
jpayne@68
|
5499 of complete PNG support, required reasonably fast floating point.
|
|
jpayne@68
|
5500
|
|
jpayne@68
|
5501 As part of this the choice of internal implementation has been made
|
|
jpayne@68
|
5502 independent of the choice of fixed versus floating point APIs and all the
|
|
jpayne@68
|
5503 missing fixed point APIs have been implemented.
|
|
jpayne@68
|
5504
|
|
jpayne@68
|
5505 The exact mechanism used to control attributes of API functions has
|
|
jpayne@68
|
5506 changed, as described in the INSTALL file.
|
|
jpayne@68
|
5507
|
|
jpayne@68
|
5508 A new test program, pngvalid, is provided in addition to pngtest.
|
|
jpayne@68
|
5509 pngvalid validates the arithmetic accuracy of the gamma correction
|
|
jpayne@68
|
5510 calculations and includes a number of validations of the file format.
|
|
jpayne@68
|
5511 A subset of the full range of tests is run when "make check" is done
|
|
jpayne@68
|
5512 (in the 'configure' build.) pngvalid also allows total allocated memory
|
|
jpayne@68
|
5513 usage to be evaluated and performs additional memory overwrite validation.
|
|
jpayne@68
|
5514
|
|
jpayne@68
|
5515 Many changes to individual feature macros have been made. The following
|
|
jpayne@68
|
5516 are the changes most likely to be noticed by library builders who
|
|
jpayne@68
|
5517 configure libpng:
|
|
jpayne@68
|
5518
|
|
jpayne@68
|
5519 1) All feature macros now have consistent naming:
|
|
jpayne@68
|
5520
|
|
jpayne@68
|
5521 #define PNG_NO_feature turns the feature off
|
|
jpayne@68
|
5522 #define PNG_feature_SUPPORTED turns the feature on
|
|
jpayne@68
|
5523
|
|
jpayne@68
|
5524 pnglibconf.h contains one line for each feature macro which is either:
|
|
jpayne@68
|
5525
|
|
jpayne@68
|
5526 #define PNG_feature_SUPPORTED
|
|
jpayne@68
|
5527
|
|
jpayne@68
|
5528 if the feature is supported or:
|
|
jpayne@68
|
5529
|
|
jpayne@68
|
5530 /*#undef PNG_feature_SUPPORTED*/
|
|
jpayne@68
|
5531
|
|
jpayne@68
|
5532 if it is not. Library code consistently checks for the 'SUPPORTED' macro.
|
|
jpayne@68
|
5533 It does not, and libpng applications should not, check for the 'NO' macro
|
|
jpayne@68
|
5534 which will not normally be defined even if the feature is not supported.
|
|
jpayne@68
|
5535 The 'NO' macros are only used internally for setting or not setting the
|
|
jpayne@68
|
5536 corresponding 'SUPPORTED' macros.
|
|
jpayne@68
|
5537
|
|
jpayne@68
|
5538 Compatibility with the old names is provided as follows:
|
|
jpayne@68
|
5539
|
|
jpayne@68
|
5540 PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
|
|
jpayne@68
|
5541
|
|
jpayne@68
|
5542 And the following definitions disable the corresponding feature:
|
|
jpayne@68
|
5543
|
|
jpayne@68
|
5544 PNG_SETJMP_NOT_SUPPORTED disables SETJMP
|
|
jpayne@68
|
5545 PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS
|
|
jpayne@68
|
5546 PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV
|
|
jpayne@68
|
5547 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS
|
|
jpayne@68
|
5548 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS
|
|
jpayne@68
|
5549 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
|
|
jpayne@68
|
5550
|
|
jpayne@68
|
5551 Library builders should remove use of the above, inconsistent, names.
|
|
jpayne@68
|
5552
|
|
jpayne@68
|
5553 2) Warning and error message formatting was previously conditional on
|
|
jpayne@68
|
5554 the STDIO feature. The library has been changed to use the
|
|
jpayne@68
|
5555 CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled
|
|
jpayne@68
|
5556 the library no longer uses the printf(3) functions, even though the
|
|
jpayne@68
|
5557 default read/write implementations use (FILE) style stdio.h functions.
|
|
jpayne@68
|
5558
|
|
jpayne@68
|
5559 3) Three feature macros now control the fixed/floating point decisions:
|
|
jpayne@68
|
5560
|
|
jpayne@68
|
5561 PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
|
|
jpayne@68
|
5562
|
|
jpayne@68
|
5563 PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in
|
|
jpayne@68
|
5564 practice these are normally required internally anyway (because the PNG
|
|
jpayne@68
|
5565 file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT
|
|
jpayne@68
|
5566 merely stops the function from being exported.
|
|
jpayne@68
|
5567
|
|
jpayne@68
|
5568 PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating
|
|
jpayne@68
|
5569 point implementation or the fixed point one. Typically the fixed point
|
|
jpayne@68
|
5570 implementation is larger and slower than the floating point implementation
|
|
jpayne@68
|
5571 on a system that supports floating point; however, it may be faster on a
|
|
jpayne@68
|
5572 system which lacks floating point hardware and therefore uses a software
|
|
jpayne@68
|
5573 emulation.
|
|
jpayne@68
|
5574
|
|
jpayne@68
|
5575 4) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the
|
|
jpayne@68
|
5576 functions to read and write ints to be disabled independently of
|
|
jpayne@68
|
5577 PNG_USE_READ_MACROS, which allows libpng to be built with the functions
|
|
jpayne@68
|
5578 even though the default is to use the macros - this allows applications
|
|
jpayne@68
|
5579 to choose at app buildtime whether or not to use macros (previously
|
|
jpayne@68
|
5580 impossible because the functions weren't in the default build.)
|
|
jpayne@68
|
5581
|
|
jpayne@68
|
5582 .SH XII. Changes to Libpng from version 1.5.x to 1.6.x
|
|
jpayne@68
|
5583
|
|
jpayne@68
|
5584 A "simplified API" has been added (see documentation in png.h and a simple
|
|
jpayne@68
|
5585 example in contrib/examples/pngtopng.c). The new publicly visible API
|
|
jpayne@68
|
5586 includes the following:
|
|
jpayne@68
|
5587
|
|
jpayne@68
|
5588 macros:
|
|
jpayne@68
|
5589 PNG_FORMAT_*
|
|
jpayne@68
|
5590 PNG_IMAGE_*
|
|
jpayne@68
|
5591 structures:
|
|
jpayne@68
|
5592 png_control
|
|
jpayne@68
|
5593 png_image
|
|
jpayne@68
|
5594 read functions
|
|
jpayne@68
|
5595 png_image_begin_read_from_file()
|
|
jpayne@68
|
5596 png_image_begin_read_from_stdio()
|
|
jpayne@68
|
5597 png_image_begin_read_from_memory()
|
|
jpayne@68
|
5598 png_image_finish_read()
|
|
jpayne@68
|
5599 png_image_free()
|
|
jpayne@68
|
5600 write functions
|
|
jpayne@68
|
5601 png_image_write_to_file()
|
|
jpayne@68
|
5602 png_image_write_to_memory()
|
|
jpayne@68
|
5603 png_image_write_to_stdio()
|
|
jpayne@68
|
5604
|
|
jpayne@68
|
5605 Starting with libpng-1.6.0, you can configure libpng to prefix all exported
|
|
jpayne@68
|
5606 symbols, using the PNG_PREFIX macro.
|
|
jpayne@68
|
5607
|
|
jpayne@68
|
5608 We no longer include string.h in png.h. The include statement has been moved
|
|
jpayne@68
|
5609 to pngpriv.h, where it is not accessible by applications. Applications that
|
|
jpayne@68
|
5610 need access to information in string.h must add an '#include <string.h>'
|
|
jpayne@68
|
5611 directive. It does not matter whether this is placed prior to or after
|
|
jpayne@68
|
5612 the '#include "png.h"' directive.
|
|
jpayne@68
|
5613
|
|
jpayne@68
|
5614 The following API are now DEPRECATED:
|
|
jpayne@68
|
5615 png_info_init_3()
|
|
jpayne@68
|
5616 png_convert_to_rfc1123() which has been replaced
|
|
jpayne@68
|
5617 with png_convert_to_rfc1123_buffer()
|
|
jpayne@68
|
5618 png_malloc_default()
|
|
jpayne@68
|
5619 png_free_default()
|
|
jpayne@68
|
5620 png_reset_zstream()
|
|
jpayne@68
|
5621
|
|
jpayne@68
|
5622 The following have been removed:
|
|
jpayne@68
|
5623 png_get_io_chunk_name(), which has been replaced
|
|
jpayne@68
|
5624 with png_get_io_chunk_type(). The new
|
|
jpayne@68
|
5625 function returns a 32-bit integer instead of
|
|
jpayne@68
|
5626 a string.
|
|
jpayne@68
|
5627 The png_sizeof(), png_strlen(), png_memcpy(), png_memcmp(), and
|
|
jpayne@68
|
5628 png_memset() macros are no longer used in the libpng sources and
|
|
jpayne@68
|
5629 have been removed. These had already been made invisible to applications
|
|
jpayne@68
|
5630 (i.e., defined in the private pngpriv.h header file) since libpng-1.5.0.
|
|
jpayne@68
|
5631
|
|
jpayne@68
|
5632 The signatures of many exported functions were changed, such that
|
|
jpayne@68
|
5633 png_structp became png_structrp or png_const_structrp
|
|
jpayne@68
|
5634 png_infop became png_inforp or png_const_inforp
|
|
jpayne@68
|
5635 where "rp" indicates a "restricted pointer".
|
|
jpayne@68
|
5636
|
|
jpayne@68
|
5637 Dropped support for 16-bit platforms. The support for FAR/far types has
|
|
jpayne@68
|
5638 been eliminated and the definition of png_alloc_size_t is now controlled
|
|
jpayne@68
|
5639 by a flag so that 'small size_t' systems can select it if necessary.
|
|
jpayne@68
|
5640
|
|
jpayne@68
|
5641 Error detection in some chunks has improved; in particular the iCCP chunk
|
|
jpayne@68
|
5642 reader now does pretty complete validation of the basic format. Some bad
|
|
jpayne@68
|
5643 profiles that were previously accepted are now accepted with a warning or
|
|
jpayne@68
|
5644 rejected, depending upon the png_set_benign_errors() setting, in particular
|
|
jpayne@68
|
5645 the very old broken Microsoft/HP 3144-byte sRGB profile. Starting with
|
|
jpayne@68
|
5646 libpng-1.6.11, recognizing and checking sRGB profiles can be avoided by
|
|
jpayne@68
|
5647 means of
|
|
jpayne@68
|
5648
|
|
jpayne@68
|
5649 #if defined(PNG_SKIP_sRGB_CHECK_PROFILE) && \
|
|
jpayne@68
|
5650 defined(PNG_SET_OPTION_SUPPORTED)
|
|
jpayne@68
|
5651 png_set_option(png_ptr, PNG_SKIP_sRGB_CHECK_PROFILE,
|
|
jpayne@68
|
5652 PNG_OPTION_ON);
|
|
jpayne@68
|
5653 #endif
|
|
jpayne@68
|
5654
|
|
jpayne@68
|
5655 It's not a good idea to do this if you are using the "simplified API",
|
|
jpayne@68
|
5656 which needs to be able to recognize sRGB profiles conveyed via the iCCP
|
|
jpayne@68
|
5657 chunk.
|
|
jpayne@68
|
5658
|
|
jpayne@68
|
5659 The PNG spec requirement that only grayscale profiles may appear in images
|
|
jpayne@68
|
5660 with color type 0 or 4 and that even if the image only contains gray pixels,
|
|
jpayne@68
|
5661 only RGB profiles may appear in images with color type 2, 3, or 6, is now
|
|
jpayne@68
|
5662 enforced. The sRGB chunk is allowed to appear in images with any color type
|
|
jpayne@68
|
5663 and is interpreted by libpng to convey a one-tracer-curve gray profile or a
|
|
jpayne@68
|
5664 three-tracer-curve RGB profile as appropriate.
|
|
jpayne@68
|
5665
|
|
jpayne@68
|
5666 Libpng 1.5.x erroneously used /MD for Debug DLL builds; if you used the debug
|
|
jpayne@68
|
5667 builds in your app and you changed your app to use /MD you will need to
|
|
jpayne@68
|
5668 change it back to /MDd for libpng 1.6.x.
|
|
jpayne@68
|
5669
|
|
jpayne@68
|
5670 Prior to libpng-1.6.0 a warning would be issued if the iTXt chunk contained
|
|
jpayne@68
|
5671 an empty language field or an empty translated keyword. Both of these
|
|
jpayne@68
|
5672 are allowed by the PNG specification, so these warnings are no longer issued.
|
|
jpayne@68
|
5673
|
|
jpayne@68
|
5674 The library now issues an error if the application attempts to set a
|
|
jpayne@68
|
5675 transform after it calls png_read_update_info() or if it attempts to call
|
|
jpayne@68
|
5676 both png_read_update_info() and png_start_read_image() or to call either
|
|
jpayne@68
|
5677 of them more than once.
|
|
jpayne@68
|
5678
|
|
jpayne@68
|
5679 The default condition for benign_errors is now to treat benign errors as
|
|
jpayne@68
|
5680 warnings while reading and as errors while writing.
|
|
jpayne@68
|
5681
|
|
jpayne@68
|
5682 The library now issues a warning if both background processing and RGB to
|
|
jpayne@68
|
5683 gray are used when gamma correction happens. As with previous versions of
|
|
jpayne@68
|
5684 the library the results are numerically very incorrect in this case.
|
|
jpayne@68
|
5685
|
|
jpayne@68
|
5686 There are some minor arithmetic changes in some transforms such as
|
|
jpayne@68
|
5687 png_set_background(), that might be detected by certain regression tests.
|
|
jpayne@68
|
5688
|
|
jpayne@68
|
5689 Unknown chunk handling has been improved internally, without any API change.
|
|
jpayne@68
|
5690 This adds more correct option control of the unknown handling, corrects
|
|
jpayne@68
|
5691 a pre-existing bug where the per-chunk 'keep' setting is ignored, and makes
|
|
jpayne@68
|
5692 it possible to skip IDAT chunks in the sequential reader.
|
|
jpayne@68
|
5693
|
|
jpayne@68
|
5694 The machine-generated configure files are no longer included in branches
|
|
jpayne@68
|
5695 libpng16 and later of the GIT repository. They continue to be included
|
|
jpayne@68
|
5696 in the tarball releases, however.
|
|
jpayne@68
|
5697
|
|
jpayne@68
|
5698 Libpng-1.6.0 through 1.6.2 used the CMF bytes at the beginning of the IDAT
|
|
jpayne@68
|
5699 stream to set the size of the sliding window for reading instead of using the
|
|
jpayne@68
|
5700 default 32-kbyte sliding window size. It was discovered that there are
|
|
jpayne@68
|
5701 hundreds of PNG files in the wild that have incorrect CMF bytes that caused
|
|
jpayne@68
|
5702 zlib to issue the "invalid distance too far back" error and reject the file.
|
|
jpayne@68
|
5703 Libpng-1.6.3 and later calculate their own safe CMF from the image dimensions,
|
|
jpayne@68
|
5704 provide a way to revert to the libpng-1.5.x behavior (ignoring the CMF bytes
|
|
jpayne@68
|
5705 and using a 32-kbyte sliding window), by using
|
|
jpayne@68
|
5706
|
|
jpayne@68
|
5707 png_set_option(png_ptr, PNG_MAXIMUM_INFLATE_WINDOW,
|
|
jpayne@68
|
5708 PNG_OPTION_ON);
|
|
jpayne@68
|
5709
|
|
jpayne@68
|
5710 and provide a tool (contrib/tools/pngfix) for rewriting a PNG file while
|
|
jpayne@68
|
5711 optimizing the CMF bytes in its IDAT chunk correctly.
|
|
jpayne@68
|
5712
|
|
jpayne@68
|
5713 Libpng-1.6.0 and libpng-1.6.1 wrote uncompressed iTXt chunks with the wrong
|
|
jpayne@68
|
5714 length, which resulted in PNG files that cannot be read beyond the bad iTXt
|
|
jpayne@68
|
5715 chunk. This error was fixed in libpng-1.6.3, and a tool (called
|
|
jpayne@68
|
5716 contrib/tools/png-fix-itxt) has been added to the libpng distribution.
|
|
jpayne@68
|
5717
|
|
jpayne@68
|
5718 Starting with libpng-1.6.17, the PNG_SAFE_LIMITS macro was eliminated
|
|
jpayne@68
|
5719 and safe limits are used by default (users who need larger limits
|
|
jpayne@68
|
5720 can still override them at compile time or run time, as described above).
|
|
jpayne@68
|
5721
|
|
jpayne@68
|
5722 The new limits are
|
|
jpayne@68
|
5723 default spec limit
|
|
jpayne@68
|
5724 png_user_width_max 1,000,000 2,147,483,647
|
|
jpayne@68
|
5725 png_user_height_max 1,000,000 2,147,483,647
|
|
jpayne@68
|
5726 png_user_chunk_cache_max 128 unlimited
|
|
jpayne@68
|
5727 png_user_chunk_malloc_max 8,000,000 unlimited
|
|
jpayne@68
|
5728
|
|
jpayne@68
|
5729 Starting with libpng-1.6.18, a PNG_RELEASE_BUILD macro was added, which allows
|
|
jpayne@68
|
5730 library builders to control compilation for an installed system (a release build).
|
|
jpayne@68
|
5731 It can be set for testing debug or beta builds to ensure that they will compile
|
|
jpayne@68
|
5732 when the build type is switched to RC or STABLE. In essence this overrides the
|
|
jpayne@68
|
5733 PNG_LIBPNG_BUILD_BASE_TYPE definition which is not directly user controllable.
|
|
jpayne@68
|
5734
|
|
jpayne@68
|
5735 Starting with libpng-1.6.19, attempting to set an over-length PLTE chunk
|
|
jpayne@68
|
5736 is an error. Previously this requirement of the PNG specification was not
|
|
jpayne@68
|
5737 enforced, and the palette was always limited to 256 entries. An over-length
|
|
jpayne@68
|
5738 PLTE chunk found in an input PNG is silently truncated.
|
|
jpayne@68
|
5739
|
|
jpayne@68
|
5740 Starting with libpng-1.6.31, the eXIf chunk is supported. Libpng does not
|
|
jpayne@68
|
5741 attempt to decode the Exif profile; it simply returns a byte array
|
|
jpayne@68
|
5742 containing the profile to the calling application which must do its own
|
|
jpayne@68
|
5743 decoding.
|
|
jpayne@68
|
5744
|
|
jpayne@68
|
5745 .SH XIII. Detecting libpng
|
|
jpayne@68
|
5746
|
|
jpayne@68
|
5747 The png_get_io_ptr() function has been present since libpng-0.88, has never
|
|
jpayne@68
|
5748 changed, and is unaffected by conditional compilation macros. It is the
|
|
jpayne@68
|
5749 best choice for use in configure scripts for detecting the presence of any
|
|
jpayne@68
|
5750 libpng version since 0.88. In an autoconf "configure.in" you could use
|
|
jpayne@68
|
5751
|
|
jpayne@68
|
5752 AC_CHECK_LIB(png, png_get_io_ptr, ...)
|
|
jpayne@68
|
5753
|
|
jpayne@68
|
5754 .SH XV. Source code repository
|
|
jpayne@68
|
5755
|
|
jpayne@68
|
5756 Since about February 2009, version 1.2.34, libpng has been under "git" source
|
|
jpayne@68
|
5757 control. The git repository was built from old libpng-x.y.z.tar.gz files
|
|
jpayne@68
|
5758 going back to version 0.70. You can access the git repository (read only)
|
|
jpayne@68
|
5759 at
|
|
jpayne@68
|
5760
|
|
jpayne@68
|
5761 https://github.com/pnggroup/libpng or
|
|
jpayne@68
|
5762 https://git.code.sf.net/p/libpng/code.git
|
|
jpayne@68
|
5763
|
|
jpayne@68
|
5764 or you can browse it with a web browser at
|
|
jpayne@68
|
5765
|
|
jpayne@68
|
5766 https://github.com/pnggroup/libpng or
|
|
jpayne@68
|
5767 https://sourceforge.net/p/libpng/code/ci/libpng16/tree/
|
|
jpayne@68
|
5768
|
|
jpayne@68
|
5769 Patches can be sent to png-mng-implement at lists.sourceforge.net or
|
|
jpayne@68
|
5770 uploaded to the libpng bug tracker at
|
|
jpayne@68
|
5771
|
|
jpayne@68
|
5772 https://libpng.sourceforge.io/
|
|
jpayne@68
|
5773
|
|
jpayne@68
|
5774 or as a "pull request" to
|
|
jpayne@68
|
5775
|
|
jpayne@68
|
5776 https://github.com/pnggroup/libpng/pulls
|
|
jpayne@68
|
5777
|
|
jpayne@68
|
5778 We also accept patches built from the tar or zip distributions, and
|
|
jpayne@68
|
5779 simple verbal descriptions of bug fixes, reported either to the
|
|
jpayne@68
|
5780 SourceForge bug tracker, to the png-mng-implement at lists.sf.net
|
|
jpayne@68
|
5781 mailing list, as github issues.
|
|
jpayne@68
|
5782
|
|
jpayne@68
|
5783 .SH XV. Coding style
|
|
jpayne@68
|
5784
|
|
jpayne@68
|
5785 Our coding style is similar to the "Allman" style
|
|
jpayne@68
|
5786 (See https://en.wikipedia.org/wiki/Indent_style#Allman_style), with curly
|
|
jpayne@68
|
5787 braces on separate lines:
|
|
jpayne@68
|
5788
|
|
jpayne@68
|
5789 if (condition)
|
|
jpayne@68
|
5790 {
|
|
jpayne@68
|
5791 action;
|
|
jpayne@68
|
5792 }
|
|
jpayne@68
|
5793
|
|
jpayne@68
|
5794 else if (another condition)
|
|
jpayne@68
|
5795 {
|
|
jpayne@68
|
5796 another action;
|
|
jpayne@68
|
5797 }
|
|
jpayne@68
|
5798
|
|
jpayne@68
|
5799 The braces can be omitted from simple one-line actions:
|
|
jpayne@68
|
5800
|
|
jpayne@68
|
5801 if (condition)
|
|
jpayne@68
|
5802 return 0;
|
|
jpayne@68
|
5803
|
|
jpayne@68
|
5804 We use 3-space indentation, except for continued statements which
|
|
jpayne@68
|
5805 are usually indented the same as the first line of the statement
|
|
jpayne@68
|
5806 plus four more spaces.
|
|
jpayne@68
|
5807
|
|
jpayne@68
|
5808 For macro definitions we use 2-space indentation, always leaving the "#"
|
|
jpayne@68
|
5809 in the first column.
|
|
jpayne@68
|
5810
|
|
jpayne@68
|
5811 #ifndef PNG_NO_FEATURE
|
|
jpayne@68
|
5812 # ifndef PNG_FEATURE_SUPPORTED
|
|
jpayne@68
|
5813 # define PNG_FEATURE_SUPPORTED
|
|
jpayne@68
|
5814 # endif
|
|
jpayne@68
|
5815 #endif
|
|
jpayne@68
|
5816
|
|
jpayne@68
|
5817 Comments appear with the leading "/*" at the same indentation as
|
|
jpayne@68
|
5818 the statement that follows the comment:
|
|
jpayne@68
|
5819
|
|
jpayne@68
|
5820 /* Single-line comment */
|
|
jpayne@68
|
5821 statement;
|
|
jpayne@68
|
5822
|
|
jpayne@68
|
5823 /* This is a multiple-line
|
|
jpayne@68
|
5824 * comment.
|
|
jpayne@68
|
5825 */
|
|
jpayne@68
|
5826 statement;
|
|
jpayne@68
|
5827
|
|
jpayne@68
|
5828 Very short comments can be placed after the end of the statement
|
|
jpayne@68
|
5829 to which they pertain:
|
|
jpayne@68
|
5830
|
|
jpayne@68
|
5831 statement; /* comment */
|
|
jpayne@68
|
5832
|
|
jpayne@68
|
5833 We don't use C++ style ("//") comments. We have, however,
|
|
jpayne@68
|
5834 used them in the past in some now-abandoned MMX assembler
|
|
jpayne@68
|
5835 code.
|
|
jpayne@68
|
5836
|
|
jpayne@68
|
5837 Functions and their curly braces are not indented, and
|
|
jpayne@68
|
5838 exported functions are marked with PNGAPI:
|
|
jpayne@68
|
5839
|
|
jpayne@68
|
5840 /* This is a public function that is visible to
|
|
jpayne@68
|
5841 * application programmers. It does thus-and-so.
|
|
jpayne@68
|
5842 */
|
|
jpayne@68
|
5843 void PNGAPI
|
|
jpayne@68
|
5844 png_exported_function(png_ptr, png_info, foo)
|
|
jpayne@68
|
5845 {
|
|
jpayne@68
|
5846 body;
|
|
jpayne@68
|
5847 }
|
|
jpayne@68
|
5848
|
|
jpayne@68
|
5849 The return type and decorations are placed on a separate line
|
|
jpayne@68
|
5850 ahead of the function name, as illustrated above.
|
|
jpayne@68
|
5851
|
|
jpayne@68
|
5852 The prototypes for all exported functions appear in png.h,
|
|
jpayne@68
|
5853 above the comment that says
|
|
jpayne@68
|
5854
|
|
jpayne@68
|
5855 /* Maintainer: Put new public prototypes here ... */
|
|
jpayne@68
|
5856
|
|
jpayne@68
|
5857 We mark all non-exported functions with "/* PRIVATE */"":
|
|
jpayne@68
|
5858
|
|
jpayne@68
|
5859 void /* PRIVATE */
|
|
jpayne@68
|
5860 png_non_exported_function(png_ptr, png_info, foo)
|
|
jpayne@68
|
5861 {
|
|
jpayne@68
|
5862 body;
|
|
jpayne@68
|
5863 }
|
|
jpayne@68
|
5864
|
|
jpayne@68
|
5865 The prototypes for non-exported functions (except for those in
|
|
jpayne@68
|
5866 pngtest) appear in pngpriv.h above the comment that says
|
|
jpayne@68
|
5867
|
|
jpayne@68
|
5868 /* Maintainer: Put new private prototypes here ^ */
|
|
jpayne@68
|
5869
|
|
jpayne@68
|
5870 To avoid polluting the global namespace, the names of all exported
|
|
jpayne@68
|
5871 functions and variables begin with "png_", and all publicly visible C
|
|
jpayne@68
|
5872 preprocessor macros begin with "PNG". We request that applications that
|
|
jpayne@68
|
5873 use libpng *not* begin any of their own symbols with either of these strings.
|
|
jpayne@68
|
5874
|
|
jpayne@68
|
5875 We put a space after the "sizeof" operator and we omit the
|
|
jpayne@68
|
5876 optional parentheses around its argument when the argument
|
|
jpayne@68
|
5877 is an expression, not a type name, and we always enclose the
|
|
jpayne@68
|
5878 sizeof operator, with its argument, in parentheses:
|
|
jpayne@68
|
5879
|
|
jpayne@68
|
5880 (sizeof (png_uint_32))
|
|
jpayne@68
|
5881 (sizeof array)
|
|
jpayne@68
|
5882
|
|
jpayne@68
|
5883 Prior to libpng-1.6.0 we used a "png_sizeof()" macro, formatted as
|
|
jpayne@68
|
5884 though it were a function.
|
|
jpayne@68
|
5885
|
|
jpayne@68
|
5886 Control keywords if, for, while, and switch are always followed by a space
|
|
jpayne@68
|
5887 to distinguish them from function calls, which have no trailing space.
|
|
jpayne@68
|
5888
|
|
jpayne@68
|
5889 We put a space after each comma and after each semicolon
|
|
jpayne@68
|
5890 in "for" statements, and we put spaces before and after each
|
|
jpayne@68
|
5891 C binary operator and after "for" or "while", and before
|
|
jpayne@68
|
5892 "?". We don't put a space between a typecast and the expression
|
|
jpayne@68
|
5893 being cast, nor do we put one between a function name and the
|
|
jpayne@68
|
5894 left parenthesis that follows it:
|
|
jpayne@68
|
5895
|
|
jpayne@68
|
5896 for (i = 2; i > 0; \-\-i)
|
|
jpayne@68
|
5897 y[i] = a(x) + (int)b;
|
|
jpayne@68
|
5898
|
|
jpayne@68
|
5899 We prefer #ifdef and #ifndef to #if defined() and #if !defined()
|
|
jpayne@68
|
5900 when there is only one macro being tested. We always use parentheses
|
|
jpayne@68
|
5901 with "defined".
|
|
jpayne@68
|
5902
|
|
jpayne@68
|
5903 We express integer constants that are used as bit masks in hex format,
|
|
jpayne@68
|
5904 with an even number of lower-case hex digits, and to make them unsigned
|
|
jpayne@68
|
5905 (e.g., 0x00U, 0xffU, 0x0100U) and long if they are greater than 0x7fff
|
|
jpayne@68
|
5906 (e.g., 0xffffUL).
|
|
jpayne@68
|
5907
|
|
jpayne@68
|
5908 We prefer to use underscores rather than camelCase in names, except
|
|
jpayne@68
|
5909 for a few type names that we inherit from zlib.h.
|
|
jpayne@68
|
5910
|
|
jpayne@68
|
5911 We prefer "if (something != 0)" and "if (something == 0)" over
|
|
jpayne@68
|
5912 "if (something)" and if "(!something)", respectively, and for pointers
|
|
jpayne@68
|
5913 we prefer "if (some_pointer != NULL)" or "if (some_pointer == NULL)".
|
|
jpayne@68
|
5914
|
|
jpayne@68
|
5915 We do not use the TAB character for indentation in the C sources.
|
|
jpayne@68
|
5916
|
|
jpayne@68
|
5917 Lines do not exceed 80 characters.
|
|
jpayne@68
|
5918
|
|
jpayne@68
|
5919 Other rules can be inferred by inspecting the libpng source.
|
|
jpayne@68
|
5920
|
|
jpayne@68
|
5921 .SH NOTE
|
|
jpayne@68
|
5922
|
|
jpayne@68
|
5923 Note about libpng version numbers:
|
|
jpayne@68
|
5924
|
|
jpayne@68
|
5925 Due to various miscommunications, unforeseen code incompatibilities
|
|
jpayne@68
|
5926 and occasional factors outside the authors' control, version numbering
|
|
jpayne@68
|
5927 on the library has not always been consistent and straightforward.
|
|
jpayne@68
|
5928 The following table summarizes matters since version 0.89c, which was
|
|
jpayne@68
|
5929 the first widely used release:
|
|
jpayne@68
|
5930
|
|
jpayne@68
|
5931 source png.h png.h shared-lib
|
|
jpayne@68
|
5932 version string int version
|
|
jpayne@68
|
5933 ------- ------ ----- ----------
|
|
jpayne@68
|
5934 0.89c "1.0 beta 3" 0.89 89 1.0.89
|
|
jpayne@68
|
5935 0.90 "1.0 beta 4" 0.90 90 0.90 [should have been 2.0.90]
|
|
jpayne@68
|
5936 0.95 "1.0 beta 5" 0.95 95 0.95 [should have been 2.0.95]
|
|
jpayne@68
|
5937 0.96 "1.0 beta 6" 0.96 96 0.96 [should have been 2.0.96]
|
|
jpayne@68
|
5938 0.97b "1.00.97 beta 7" 1.00.97 97 1.0.1 [should have been 2.0.97]
|
|
jpayne@68
|
5939 0.97c 0.97 97 2.0.97
|
|
jpayne@68
|
5940 0.98 0.98 98 2.0.98
|
|
jpayne@68
|
5941 0.99 0.99 98 2.0.99
|
|
jpayne@68
|
5942 0.99a-m 0.99 99 2.0.99
|
|
jpayne@68
|
5943 1.00 1.00 100 2.1.0 [100 should be 10000]
|
|
jpayne@68
|
5944 1.0.0 (from here on, the 100 2.1.0 [100 should be 10000]
|
|
jpayne@68
|
5945 1.0.1 png.h string is 10001 2.1.0
|
|
jpayne@68
|
5946 1.0.1a-e identical to the 10002 from here on, the shared library
|
|
jpayne@68
|
5947 1.0.2 source version) 10002 is 2.V where V is the source code
|
|
jpayne@68
|
5948 1.0.2a-b 10003 version, except as noted.
|
|
jpayne@68
|
5949 1.0.3 10003
|
|
jpayne@68
|
5950 1.0.3a-d 10004
|
|
jpayne@68
|
5951 1.0.4 10004
|
|
jpayne@68
|
5952 1.0.4a-f 10005
|
|
jpayne@68
|
5953 1.0.5 (+ 2 patches) 10005
|
|
jpayne@68
|
5954 1.0.5a-d 10006
|
|
jpayne@68
|
5955 1.0.5e-r 10100 (not source compatible)
|
|
jpayne@68
|
5956 1.0.5s-v 10006 (not binary compatible)
|
|
jpayne@68
|
5957 1.0.6 (+ 3 patches) 10006 (still binary incompatible)
|
|
jpayne@68
|
5958 1.0.6d-f 10007 (still binary incompatible)
|
|
jpayne@68
|
5959 1.0.6g 10007
|
|
jpayne@68
|
5960 1.0.6h 10007 10.6h (testing xy.z so-numbering)
|
|
jpayne@68
|
5961 1.0.6i 10007 10.6i
|
|
jpayne@68
|
5962 1.0.6j 10007 2.1.0.6j (incompatible with 1.0.0)
|
|
jpayne@68
|
5963 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14 (binary compatible)
|
|
jpayne@68
|
5964 1.0.7beta15-18 1 10007 2.1.0.7beta15-18 (binary compatible)
|
|
jpayne@68
|
5965 1.0.7rc1-2 1 10007 2.1.0.7rc1-2 (binary compatible)
|
|
jpayne@68
|
5966 1.0.7 1 10007 (still compatible)
|
|
jpayne@68
|
5967 ...
|
|
jpayne@68
|
5968 1.0.69 10 10069 10.so.0.69[.0]
|
|
jpayne@68
|
5969 ...
|
|
jpayne@68
|
5970 1.2.59 13 10259 12.so.0.59[.0]
|
|
jpayne@68
|
5971 ...
|
|
jpayne@68
|
5972 1.4.20 14 10420 14.so.0.20[.0]
|
|
jpayne@68
|
5973 ...
|
|
jpayne@68
|
5974 1.5.30 15 10530 15.so.15.30[.0]
|
|
jpayne@68
|
5975 ...
|
|
jpayne@68
|
5976 1.6.35 16 10635 16.so.16.35[.0]
|
|
jpayne@68
|
5977
|
|
jpayne@68
|
5978 Henceforth the source version will match the shared-library minor and
|
|
jpayne@68
|
5979 patch numbers; the shared-library major version number will be used for
|
|
jpayne@68
|
5980 changes in backward compatibility, as it is intended.
|
|
jpayne@68
|
5981 The PNG_PNGLIB_VER macro, which is not used within libpng but is
|
|
jpayne@68
|
5982 available for applications, is an unsigned integer of the form XYYZZ
|
|
jpayne@68
|
5983 corresponding to the source version X.Y.Z (leading zeros in Y and Z).
|
|
jpayne@68
|
5984 Beta versions were given the previous public release number plus a
|
|
jpayne@68
|
5985 letter, until version 1.0.6j; from then on they were given the upcoming
|
|
jpayne@68
|
5986 public release number plus "betaNN" or "rcNN".
|
|
jpayne@68
|
5987
|
|
jpayne@68
|
5988 .SH "SEE ALSO"
|
|
jpayne@68
|
5989 .BR "png"(5)
|
|
jpayne@68
|
5990 .IP
|
|
jpayne@68
|
5991 The PNG (Portable Network Graphics) format specification.
|
|
jpayne@68
|
5992 .LP
|
|
jpayne@68
|
5993 .B libpng
|
|
jpayne@68
|
5994 .IP
|
|
jpayne@68
|
5995 http://www.libpng.org/pub/png/libpng.html (canonical home page)
|
|
jpayne@68
|
5996 .br
|
|
jpayne@68
|
5997 https://github.com/pnggroup/libpng (canonical Git repository)
|
|
jpayne@68
|
5998 .br
|
|
jpayne@68
|
5999 https://libpng.sourceforge.io (downloadable archives)
|
|
jpayne@68
|
6000 .LP
|
|
jpayne@68
|
6001 .B zlib
|
|
jpayne@68
|
6002 .IP
|
|
jpayne@68
|
6003 https://zlib.net (canonical home page)
|
|
jpayne@68
|
6004 .br
|
|
jpayne@68
|
6005 https://github.com/madler/zlib (canonical Git repository)
|
|
jpayne@68
|
6006 .br
|
|
jpayne@68
|
6007 A copy of zlib may also be found at the same location as libpng.
|
|
jpayne@68
|
6008 .LP
|
|
jpayne@68
|
6009 In the case of any inconsistency between the PNG specification
|
|
jpayne@68
|
6010 and this library, the specification takes precedence.
|
|
jpayne@68
|
6011
|
|
jpayne@68
|
6012 .SH AUTHORS
|
|
jpayne@68
|
6013 This man page:
|
|
jpayne@68
|
6014 Initially created by Glenn Randers-Pehrson.
|
|
jpayne@68
|
6015 Maintained by Cosmin Truta.
|
|
jpayne@68
|
6016
|
|
jpayne@68
|
6017 The contributing authors would like to thank all those who helped
|
|
jpayne@68
|
6018 with testing, bug fixes, and patience. This wouldn't have been
|
|
jpayne@68
|
6019 possible without all of you.
|
|
jpayne@68
|
6020
|
|
jpayne@68
|
6021 Thanks to Frank J. T. Wojcik for helping with the documentation.
|
|
jpayne@68
|
6022
|
|
jpayne@68
|
6023 Libpng:
|
|
jpayne@68
|
6024 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
|
|
jpayne@68
|
6025 Maintained by Cosmin Truta.
|
|
jpayne@68
|
6026
|
|
jpayne@68
|
6027 Supported by the PNG development group.
|
|
jpayne@68
|
6028 .br
|
|
jpayne@68
|
6029 png-mng-implement at lists.sourceforge.net. (Subscription is required;
|
|
jpayne@68
|
6030 visit https://lists.sourceforge.net/lists/listinfo/png-mng-implement
|
|
jpayne@68
|
6031 to subscribe.)
|
|
jpayne@68
|
6032
|
|
jpayne@68
|
6033 .\" end of man page
|
