jpayne@68: .TH LIBPNG 3 "February 23, 2024" jpayne@68: .SH NAME jpayne@68: libpng \- Portable Network Graphics (PNG) Reference Library 1.6.43 jpayne@68: jpayne@68: .SH SYNOPSIS jpayne@68: \fB#include \fP jpayne@68: jpayne@68: \fBpng_uint_32 png_access_version_number (void);\fP jpayne@68: jpayne@68: \fBvoid png_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_build_grayscale_palette (int \fP\fIbit_depth\fP\fB, png_colorp \fIpalette\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_voidp png_calloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_err (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_free_default (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_byte png_get_bit_depth (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBpng_byte png_get_channels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBpng_uint_32 png_get_chunk_cache_max (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_alloc_size_t png_get_chunk_malloc_max (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_byte png_get_color_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_uint_32 png_get_compression_buffer_size (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_byte png_get_compression_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_byte png_get_copyright (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_uint_32 png_get_current_row_number \fI(png_const_structp\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_byte png_get_current_pass_number \fI(png_const_structp\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_voidp png_get_error_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_byte png_get_filter_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBpng_byte png_get_header_ver (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_byte png_get_header_version (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBpng_uint_32 png_get_image_height (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_uint_32 png_get_image_width (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_byte png_get_interlace_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBint png_get_palette_max(png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fB/* This function is really an inline macro. \fI*/ jpayne@68: jpayne@68: \fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP jpayne@68: jpayne@68: \fB/* This function is really an inline macro. \fI*/ jpayne@68: jpayne@68: \fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_int_32 png_get_x_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_int_32 png_get_y_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP jpayne@68: jpayne@68: \fBint png_image_begin_read_from_file (png_imagep \fP\fIimage\fP\fB, const char \fI*file_name\fP\fB);\fP jpayne@68: jpayne@68: \fBint png_image_begin_read_from_stdio (png_imagep \fP\fIimage\fP\fB, FILE* \fIfile\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_image_free (png_imagep \fIimage\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, size_t \fIpng_info_struct_size\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBsize_t png_process_data_pause (png_structp \fP\fIpng_ptr\fP\fB, int \fIsave\fP\fB);\fP jpayne@68: jpayne@68: \fBpng_uint_32 png_process_data_skip (png_structp \fP\fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_alpha_mode (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, double \fIoutput_gamma\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_check_for_invalid_index (png_structrp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_eXIf (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fIexif\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBint png_set_option(png_structrp \fP\fIpng_ptr\fP\fB, int \fP\fIoption\fP\fB, int \fIonoff\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_scale_16 (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_text_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_text_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_text_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_text_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_set_text_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBint png_sig_cmp (png_bytep \fP\fIsig\fP\fB, size_t \fP\fIstart\fP\fB, size_t \fInum_to_check\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_write_chunk_data (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIdata\fP\fB, size_t \fIlength\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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: jpayne@68: \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP jpayne@68: jpayne@68: \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 jpayne@68: jpayne@68: \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP jpayne@68: jpayne@68: \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: jpayne@68: \fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP jpayne@68: jpayne@68: .SH DESCRIPTION jpayne@68: The jpayne@68: .I libpng jpayne@68: library supports encoding, decoding, and various manipulations of jpayne@68: the Portable Network Graphics (PNG) format image files. It uses the jpayne@68: .IR zlib(3) jpayne@68: compression library. jpayne@68: Following is a copy of the libpng-manual.txt file that accompanies libpng. jpayne@68: jpayne@68: .SH LIBPNG.TXT jpayne@68: libpng-manual.txt - A description on how to use and modify libpng jpayne@68: jpayne@68: Copyright (c) 2018-2024 Cosmin Truta jpayne@68: Copyright (c) 1998-2018 Glenn Randers-Pehrson jpayne@68: jpayne@68: This document is released under the libpng license. jpayne@68: For conditions of distribution and use, see the disclaimer jpayne@68: and license in png.h jpayne@68: jpayne@68: Based on: jpayne@68: jpayne@68: libpng version 1.6.36, December 2018, through 1.6.43 - February 2024 jpayne@68: Updated and distributed by Cosmin Truta jpayne@68: Copyright (c) 2018-2024 Cosmin Truta jpayne@68: jpayne@68: libpng versions 0.97, January 1998, through 1.6.35 - July 2018 jpayne@68: Updated and distributed by Glenn Randers-Pehrson jpayne@68: Copyright (c) 1998-2018 Glenn Randers-Pehrson jpayne@68: jpayne@68: libpng 1.0 beta 6 - version 0.96 - May 28, 1997 jpayne@68: Updated and distributed by Andreas Dilger jpayne@68: Copyright (c) 1996, 1997 Andreas Dilger jpayne@68: jpayne@68: libpng 1.0 beta 2 - version 0.88 - January 26, 1996 jpayne@68: For conditions of distribution and use, see copyright jpayne@68: notice in png.h. Copyright (c) 1995, 1996 Guy Eric jpayne@68: Schalnat, Group 42, Inc. jpayne@68: jpayne@68: Updated/rewritten per request in the libpng FAQ jpayne@68: Copyright (c) 1995, 1996 Frank J. T. Wojcik jpayne@68: December 18, 1995 & January 20, 1996 jpayne@68: jpayne@68: TABLE OF CONTENTS jpayne@68: jpayne@68: I. Introduction jpayne@68: II. Structures jpayne@68: III. Reading jpayne@68: IV. Writing jpayne@68: V. Simplified API jpayne@68: VI. Modifying/Customizing libpng jpayne@68: VII. MNG support jpayne@68: VIII. Changes to Libpng from version 0.88 jpayne@68: IX. Changes to Libpng from version 1.0.x to 1.2.x jpayne@68: X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x jpayne@68: XI. Changes to Libpng from version 1.4.x to 1.5.x jpayne@68: XII. Changes to Libpng from version 1.5.x to 1.6.x jpayne@68: XIII. Detecting libpng jpayne@68: XIV. Source code repository jpayne@68: XV. Coding style jpayne@68: jpayne@68: .SH I. Introduction jpayne@68: jpayne@68: This file describes how to use and modify the PNG reference library jpayne@68: (known as libpng) for your own use. In addition to this jpayne@68: file, example.c is a good starting point for using the library, as jpayne@68: it is heavily commented and should include everything most people jpayne@68: will need. We assume that libpng is already installed; see the jpayne@68: INSTALL file for instructions on how to configure and install libpng. jpayne@68: jpayne@68: For examples of libpng usage, see the files "example.c", "pngtest.c", jpayne@68: and the files in the "contrib" directory, all of which are included in jpayne@68: the libpng distribution. jpayne@68: jpayne@68: Libpng was written as a companion to the PNG specification, as a way jpayne@68: of reducing the amount of time and effort it takes to support the PNG jpayne@68: file format in application programs. jpayne@68: jpayne@68: The PNG specification (second edition), November 2003, is available as jpayne@68: a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2004 (E)) at jpayne@68: . jpayne@68: The W3C and ISO documents have identical technical content. jpayne@68: jpayne@68: The PNG-1.2 specification is available at jpayne@68: . jpayne@68: It is technically equivalent jpayne@68: to the PNG specification (second edition) but has some additional material. jpayne@68: jpayne@68: The PNG-1.0 specification is available as RFC 2083 at jpayne@68: and as a jpayne@68: W3C Recommendation at . jpayne@68: jpayne@68: Some additional chunks are described in the special-purpose public chunks jpayne@68: documents at jpayne@68: jpayne@68: Other information jpayne@68: about PNG, and the latest version of libpng, can be found at the PNG home jpayne@68: page, . jpayne@68: jpayne@68: Most users will not have to modify the library significantly; advanced jpayne@68: users may want to modify it more. All attempts were made to make it as jpayne@68: complete as possible, while keeping the code easy to understand. jpayne@68: Currently, this library only supports C. Support for other languages jpayne@68: is being considered. jpayne@68: jpayne@68: Libpng has been designed to handle multiple sessions at one time, jpayne@68: to be easily modifiable, to be portable to the vast majority of jpayne@68: machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy jpayne@68: to use. The ultimate goal of libpng is to promote the acceptance of jpayne@68: the PNG file format in whatever way possible. While there is still jpayne@68: work to be done (see the TODO file), libpng should cover the jpayne@68: majority of the needs of its users. jpayne@68: jpayne@68: Libpng uses zlib for its compression and decompression of PNG files. jpayne@68: Further information about zlib, and the latest version of zlib, can jpayne@68: be found at the zlib home page, . jpayne@68: The zlib compression utility is a general purpose utility that is jpayne@68: useful for more than PNG files, and can be used without libpng. jpayne@68: See the documentation delivered with zlib for more details. jpayne@68: You can usually find the source files for the zlib utility wherever you jpayne@68: find the libpng source files. jpayne@68: jpayne@68: Libpng is thread safe, provided the threads are using different jpayne@68: instances of the structures. Each thread should have its own jpayne@68: png_struct and png_info instances, and thus its own image. jpayne@68: Libpng does not protect itself against two threads using the jpayne@68: same instance of a structure. jpayne@68: jpayne@68: .SH II. Structures jpayne@68: jpayne@68: There are two main structures that are important to libpng, png_struct jpayne@68: and png_info. Both are internal structures that are no longer exposed jpayne@68: in the libpng interface (as of libpng 1.5.0). jpayne@68: jpayne@68: The png_info structure is designed to provide information about the jpayne@68: PNG file. At one time, the fields of png_info were intended to be jpayne@68: directly accessible to the user. However, this tended to cause problems jpayne@68: with applications using dynamically loaded libraries, and as a result jpayne@68: a set of interface functions for png_info (the png_get_*() and png_set_*() jpayne@68: functions) was developed, and direct access to the png_info fields was jpayne@68: deprecated.. jpayne@68: jpayne@68: The png_struct structure is the object used by the library to decode a jpayne@68: single image. As of 1.5.0 this structure is also not exposed. jpayne@68: jpayne@68: Almost all libpng APIs require a pointer to a png_struct as the first argument. jpayne@68: Many (in particular the png_set and png_get APIs) also require a pointer jpayne@68: to png_info as the second argument. Some application visible macros jpayne@68: defined in png.h designed for basic data access (reading and writing jpayne@68: integers in the PNG format) don't take a png_info pointer, but it's almost jpayne@68: always safe to assume that a (png_struct*) has to be passed to call an API jpayne@68: function. jpayne@68: jpayne@68: You can have more than one png_info structure associated with an image, jpayne@68: as illustrated in pngtest.c, one for information valid prior to the jpayne@68: IDAT chunks and another (called "end_info" below) for things after them. jpayne@68: jpayne@68: The png.h header file is an invaluable reference for programming with libpng. jpayne@68: And while I'm on the topic, make sure you include the libpng header file: jpayne@68: jpayne@68: #include jpayne@68: jpayne@68: and also (as of libpng-1.5.0) the zlib header file, if you need it: jpayne@68: jpayne@68: #include jpayne@68: jpayne@68: .SS Types jpayne@68: jpayne@68: The png.h header file defines a number of integral types used by the jpayne@68: APIs. Most of these are fairly obvious; for example types corresponding jpayne@68: to integers of particular sizes and types for passing color values. jpayne@68: jpayne@68: One exception is how non-integral numbers are handled. For application jpayne@68: convenience most APIs that take such numbers have C (double) arguments; jpayne@68: however, internally PNG, and libpng, use 32 bit signed integers and encode jpayne@68: the value by multiplying by 100,000. As of libpng 1.5.0 a convenience jpayne@68: macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point) jpayne@68: which is simply (png_int_32). jpayne@68: jpayne@68: All APIs that take (double) arguments also have a matching API that jpayne@68: takes the corresponding fixed point integer arguments. The fixed point jpayne@68: API has the same name as the floating point one with "_fixed" appended. jpayne@68: The actual range of values permitted in the APIs is frequently less than jpayne@68: the full range of (png_fixed_point) (\-21474 to +21474). When APIs require jpayne@68: a non-negative argument the type is recorded as png_uint_32 above. Consult jpayne@68: the header file and the text below for more information. jpayne@68: jpayne@68: Special care must be take with sCAL chunk handling because the chunk itself jpayne@68: uses non-integral values encoded as strings containing decimal floating point jpayne@68: numbers. See the comments in the header file. jpayne@68: jpayne@68: .SS Configuration jpayne@68: jpayne@68: The main header file function declarations are frequently protected by C jpayne@68: preprocessing directives of the form: jpayne@68: jpayne@68: #ifdef PNG_feature_SUPPORTED jpayne@68: declare-function jpayne@68: #endif jpayne@68: ... jpayne@68: #ifdef PNG_feature_SUPPORTED jpayne@68: use-function jpayne@68: #endif jpayne@68: jpayne@68: The library can be built without support for these APIs, although a jpayne@68: standard build will have all implemented APIs. Application programs jpayne@68: should check the feature macros before using an API for maximum jpayne@68: portability. From libpng 1.5.0 the feature macros set during the build jpayne@68: of libpng are recorded in the header file "pnglibconf.h" and this file jpayne@68: is always included by png.h. jpayne@68: jpayne@68: If you don't need to change the library configuration from the default, skip to jpayne@68: the next section ("Reading"). jpayne@68: jpayne@68: Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all jpayne@68: of the build project files in the 'projects' directory simply copy jpayne@68: scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build jpayne@68: systems do not permit easy auto-configuration of the library - they only jpayne@68: support the default configuration. jpayne@68: jpayne@68: The easiest way to make minor changes to the libpng configuration when jpayne@68: auto-configuration is supported is to add definitions to the command line jpayne@68: using (typically) CPPFLAGS. For example: jpayne@68: jpayne@68: CPPFLAGS=\-DPNG_NO_FLOATING_ARITHMETIC jpayne@68: jpayne@68: will change the internal libpng math implementation for gamma correction and jpayne@68: other arithmetic calculations to fixed point, avoiding the need for fast jpayne@68: floating point support. The result can be seen in the generated pnglibconf.h - jpayne@68: make sure it contains the changed feature macro setting. jpayne@68: jpayne@68: If you need to make more extensive configuration changes - more than one or two jpayne@68: feature macro settings - you can either add \-DPNG_USER_CONFIG to the build jpayne@68: command line and put a list of feature macro settings in pngusr.h or you can set jpayne@68: DFA_XTRA (a makefile variable) to a file containing the same information in the jpayne@68: form of 'option' settings. jpayne@68: jpayne@68: A. Changing pnglibconf.h jpayne@68: jpayne@68: A variety of methods exist to build libpng. Not all of these support jpayne@68: reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be jpayne@68: rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand. jpayne@68: jpayne@68: Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to jpayne@68: pnglibconf.h and changing the lines defining the supported features, paying jpayne@68: very close attention to the 'option' information in scripts/pnglibconf.dfa jpayne@68: that describes those features and their requirements. This is easy to get jpayne@68: wrong. jpayne@68: jpayne@68: B. Configuration using DFA_XTRA jpayne@68: jpayne@68: Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later jpayne@68: variant such as 'nawk' or 'gawk', is available. The configure build will jpayne@68: automatically find an appropriate awk and build pnglibconf.h. jpayne@68: The scripts/pnglibconf.mak file contains a set of make rules for doing the jpayne@68: same thing if configure is not used, and many of the makefiles in the scripts jpayne@68: directory use this approach. jpayne@68: jpayne@68: When rebuilding simply write a new file containing changed options and set jpayne@68: DFA_XTRA to the name of this file. This causes the build to append the new file jpayne@68: to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines jpayne@68: of the following forms: jpayne@68: jpayne@68: everything = off jpayne@68: jpayne@68: This turns all optional features off. Include it at the start of pngusr.dfa to jpayne@68: make it easier to build a minimal configuration. You will need to turn at least jpayne@68: some features on afterward to enable either reading or writing code, or both. jpayne@68: jpayne@68: option feature on jpayne@68: option feature off jpayne@68: jpayne@68: Enable or disable a single feature. This will automatically enable other jpayne@68: features required by a feature that is turned on or disable other features that jpayne@68: require a feature which is turned off. Conflicting settings will cause an error jpayne@68: message to be emitted by awk. jpayne@68: jpayne@68: setting feature default value jpayne@68: jpayne@68: Changes the default value of setting 'feature' to 'value'. There are a small jpayne@68: number of settings listed at the top of pnglibconf.h, they are documented in the jpayne@68: source code. Most of these values have performance implications for the library jpayne@68: but most of them have no visible effect on the API. Some can also be overridden jpayne@68: from the API. jpayne@68: jpayne@68: This method of building a customized pnglibconf.h is illustrated in jpayne@68: contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and jpayne@68: pngusr.dfa in these directories. jpayne@68: jpayne@68: C. Configuration using PNG_USER_CONFIG jpayne@68: jpayne@68: If \-DPNG_USER_CONFIG is added to the CPPFLAGS when pnglibconf.h is built, jpayne@68: the file pngusr.h will automatically be included before the options in jpayne@68: scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only jpayne@68: macro definitions turning features on or off or setting settings. jpayne@68: jpayne@68: Apart from the global setting "everything = off" all the options listed above jpayne@68: can be set using macros in pngusr.h: jpayne@68: jpayne@68: #define PNG_feature_SUPPORTED jpayne@68: jpayne@68: is equivalent to: jpayne@68: jpayne@68: option feature on jpayne@68: jpayne@68: #define PNG_NO_feature jpayne@68: jpayne@68: is equivalent to: jpayne@68: jpayne@68: option feature off jpayne@68: jpayne@68: #define PNG_feature value jpayne@68: jpayne@68: is equivalent to: jpayne@68: jpayne@68: setting feature default value jpayne@68: jpayne@68: Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the jpayne@68: pngusr file you supply override the contents of scripts/pnglibconf.dfa jpayne@68: jpayne@68: If confusing or incomprehensible behavior results it is possible to jpayne@68: examine the intermediate file pnglibconf.dfn to find the full set of jpayne@68: dependency information for each setting and option. Simply locate the jpayne@68: feature in the file and read the C comments that precede it. jpayne@68: jpayne@68: This method is also illustrated in the contrib/pngminim/* makefiles and jpayne@68: pngusr.h. jpayne@68: jpayne@68: .SH III. Reading jpayne@68: jpayne@68: We'll now walk you through the possible functions to call when reading jpayne@68: in a PNG file sequentially, briefly explaining the syntax and purpose jpayne@68: of each one. See example.c and png.h for more detail. While jpayne@68: progressive reading is covered in the next section, you will still jpayne@68: need some of the functions discussed in this section to read a PNG jpayne@68: file. jpayne@68: jpayne@68: .SS Setup jpayne@68: jpayne@68: You will want to do the I/O initialization(*) before you get into libpng, jpayne@68: so if it doesn't work, you don't have much to undo. Of course, you jpayne@68: will also want to insure that you are, in fact, dealing with a PNG jpayne@68: file. Libpng provides a simple check to see if a file is a PNG file. jpayne@68: To use it, pass in the first 1 to 8 bytes of the file to the function jpayne@68: png_sig_cmp(), and it will return 0 (false) if the bytes match the jpayne@68: corresponding bytes of the PNG signature, or nonzero (true) otherwise. jpayne@68: Of course, the more bytes you pass in, the greater the accuracy of the jpayne@68: prediction. jpayne@68: jpayne@68: If you are intending to keep the file pointer open for use in libpng, jpayne@68: you must ensure you don't read more than 8 bytes from the beginning jpayne@68: of the file, and you also have to make a call to png_set_sig_bytes() jpayne@68: with the number of bytes you read from the beginning. Libpng will jpayne@68: then only check the bytes (if any) that your program didn't read. jpayne@68: jpayne@68: (*): If you are not using the standard I/O functions, you will need jpayne@68: to replace them with custom functions. See the discussion under jpayne@68: Customizing libpng. jpayne@68: jpayne@68: FILE *fp = fopen(file_name, "rb"); jpayne@68: if (!fp) jpayne@68: { jpayne@68: return ERROR; jpayne@68: } jpayne@68: jpayne@68: if (fread(header, 1, number, fp) != number) jpayne@68: { jpayne@68: return ERROR; jpayne@68: } jpayne@68: jpayne@68: is_png = (png_sig_cmp(header, 0, number) == 0); jpayne@68: if (!is_png) jpayne@68: { jpayne@68: return NOT_PNG; jpayne@68: } jpayne@68: jpayne@68: Next, png_struct and png_info need to be allocated and initialized. In jpayne@68: order to ensure that the size of these structures is correct even with a jpayne@68: dynamically linked libpng, there are functions to initialize and jpayne@68: allocate the structures. We also pass the library version, optional jpayne@68: pointers to error handling functions, and a pointer to a data struct for jpayne@68: use by the error functions, if necessary (the pointer and functions can jpayne@68: be NULL if the default error handlers are to be used). See the section jpayne@68: on Changes to Libpng below regarding the old initialization functions. jpayne@68: The structure allocation functions quietly return NULL if they fail to jpayne@68: create the structure, so your application should check for that. jpayne@68: jpayne@68: png_structp png_ptr = png_create_read_struct jpayne@68: (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, jpayne@68: user_error_fn, user_warning_fn); jpayne@68: jpayne@68: if (!png_ptr) jpayne@68: return ERROR; jpayne@68: jpayne@68: png_infop info_ptr = png_create_info_struct(png_ptr); jpayne@68: jpayne@68: if (!info_ptr) jpayne@68: { jpayne@68: png_destroy_read_struct(&png_ptr, NULL, NULL); jpayne@68: return ERROR; jpayne@68: } jpayne@68: jpayne@68: If you want to use your own memory allocation routines, jpayne@68: use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use jpayne@68: png_create_read_struct_2() instead of png_create_read_struct(): jpayne@68: jpayne@68: png_structp png_ptr = png_create_read_struct_2 jpayne@68: (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, jpayne@68: user_error_fn, user_warning_fn, (png_voidp) jpayne@68: user_mem_ptr, user_malloc_fn, user_free_fn); jpayne@68: jpayne@68: The error handling routines passed to png_create_read_struct() jpayne@68: and the memory alloc/free routines passed to png_create_struct_2() jpayne@68: are only necessary if you are not using the libpng supplied error jpayne@68: handling and memory alloc/free functions. jpayne@68: jpayne@68: When libpng encounters an error, it expects to longjmp back jpayne@68: to your routine. Therefore, you will need to call setjmp and pass jpayne@68: your png_jmpbuf(png_ptr). If you read the file from different jpayne@68: routines, you will need to update the longjmp buffer every time you enter jpayne@68: a new routine that will call a png_*() function. jpayne@68: jpayne@68: See your documentation of setjmp/longjmp for your compiler for more jpayne@68: information on setjmp/longjmp. See the discussion on libpng error jpayne@68: handling in the Customizing Libpng section below for more information jpayne@68: on the libpng error handling. If an error occurs, and libpng longjmp's jpayne@68: back to your setjmp, you will want to call png_destroy_read_struct() to jpayne@68: free any memory. jpayne@68: jpayne@68: if (setjmp(png_jmpbuf(png_ptr))) jpayne@68: { jpayne@68: png_destroy_read_struct(&png_ptr, &info_ptr, &end_info); jpayne@68: fclose(fp); jpayne@68: return ERROR; jpayne@68: } jpayne@68: jpayne@68: Pass NULL instead of &end_info if you didn't create an end_info jpayne@68: structure. jpayne@68: jpayne@68: If you would rather avoid the complexity of setjmp/longjmp issues, jpayne@68: you can compile libpng with PNG_NO_SETJMP, in which case jpayne@68: errors will result in a call to PNG_ABORT() which defaults to abort(). jpayne@68: jpayne@68: You can #define PNG_ABORT() to a function that does something jpayne@68: more useful than abort(), as long as your function does not jpayne@68: return. jpayne@68: jpayne@68: Now you need to set up the input code. The default for libpng is to jpayne@68: use the C function fread(). If you use this, you will need to pass a jpayne@68: valid FILE * in the function png_init_io(). Be sure that the file is jpayne@68: opened in binary mode. If you wish to handle reading data in another jpayne@68: way, you need not call the png_init_io() function, but you must then jpayne@68: implement the libpng I/O methods discussed in the Customizing Libpng jpayne@68: section below. jpayne@68: jpayne@68: png_init_io(png_ptr, fp); jpayne@68: jpayne@68: If you had previously opened the file and read any of the signature from jpayne@68: the beginning in order to see if this was a PNG file, you need to let jpayne@68: libpng know that there are some bytes missing from the start of the file. jpayne@68: jpayne@68: png_set_sig_bytes(png_ptr, number); jpayne@68: jpayne@68: You can change the zlib compression buffer size to be used while jpayne@68: reading compressed data with jpayne@68: jpayne@68: png_set_compression_buffer_size(png_ptr, buffer_size); jpayne@68: jpayne@68: where the default size is 8192 bytes. Note that the buffer size jpayne@68: is changed immediately and the buffer is reallocated immediately, jpayne@68: instead of setting a flag to be acted upon later. jpayne@68: jpayne@68: If you want CRC errors to be handled in a different manner than jpayne@68: the default, use jpayne@68: jpayne@68: png_set_crc_action(png_ptr, crit_action, ancil_action); jpayne@68: jpayne@68: The values for png_set_crc_action() say how libpng is to handle CRC errors in jpayne@68: ancillary and critical chunks, and whether to use the data contained jpayne@68: therein. Starting with libpng-1.6.26, this also governs how an ADLER32 error jpayne@68: is handled while reading the IDAT chunk. Note that it is impossible to jpayne@68: "discard" data in a critical chunk. jpayne@68: jpayne@68: Choices for (int) crit_action are jpayne@68: PNG_CRC_DEFAULT 0 error/quit jpayne@68: PNG_CRC_ERROR_QUIT 1 error/quit jpayne@68: PNG_CRC_WARN_USE 3 warn/use data jpayne@68: PNG_CRC_QUIET_USE 4 quiet/use data jpayne@68: PNG_CRC_NO_CHANGE 5 use the current value jpayne@68: jpayne@68: Choices for (int) ancil_action are jpayne@68: PNG_CRC_DEFAULT 0 error/quit jpayne@68: PNG_CRC_ERROR_QUIT 1 error/quit jpayne@68: PNG_CRC_WARN_DISCARD 2 warn/discard data jpayne@68: PNG_CRC_WARN_USE 3 warn/use data jpayne@68: PNG_CRC_QUIET_USE 4 quiet/use data jpayne@68: PNG_CRC_NO_CHANGE 5 use the current value jpayne@68: jpayne@68: When the setting for crit_action is PNG_CRC_QUIET_USE, the CRC and ADLER32 jpayne@68: checksums are not only ignored, but they are not evaluated. jpayne@68: jpayne@68: .SS Setting up callback code jpayne@68: jpayne@68: You can set up a callback function to handle any unknown chunks in the jpayne@68: input stream. You must supply the function jpayne@68: jpayne@68: read_chunk_callback(png_structp png_ptr, jpayne@68: png_unknown_chunkp chunk) jpayne@68: { jpayne@68: /* The unknown chunk structure contains your jpayne@68: chunk data, along with similar data for any other jpayne@68: unknown chunks: */ jpayne@68: jpayne@68: png_byte name[5]; jpayne@68: png_byte *data; jpayne@68: size_t size; jpayne@68: jpayne@68: /* Note that libpng has already taken care of jpayne@68: the CRC handling */ jpayne@68: jpayne@68: /* put your code here. Search for your chunk in the jpayne@68: unknown chunk structure, process it, and return one jpayne@68: of the following: */ jpayne@68: jpayne@68: return \-n; /* chunk had an error */ jpayne@68: return 0; /* did not recognize */ jpayne@68: return n; /* success */ jpayne@68: } jpayne@68: jpayne@68: (You can give your function another name that you like instead of jpayne@68: "read_chunk_callback") jpayne@68: jpayne@68: To inform libpng about your function, use jpayne@68: jpayne@68: png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr, jpayne@68: read_chunk_callback); jpayne@68: jpayne@68: This names not only the callback function, but also a user pointer that jpayne@68: you can retrieve with jpayne@68: jpayne@68: png_get_user_chunk_ptr(png_ptr); jpayne@68: jpayne@68: If you call the png_set_read_user_chunk_fn() function, then all unknown jpayne@68: chunks which the callback does not handle will be saved when read. You can jpayne@68: cause them to be discarded by returning '1' ("handled") instead of '0'. This jpayne@68: behavior will change in libpng 1.7 and the default handling set by the jpayne@68: png_set_keep_unknown_chunks() function, described below, will be used when the jpayne@68: callback returns 0. If you want the existing behavior you should set the global jpayne@68: default to PNG_HANDLE_CHUNK_IF_SAFE now; this is compatible with all current jpayne@68: versions of libpng and with 1.7. Libpng 1.6 issues a warning if you keep the jpayne@68: default, or PNG_HANDLE_CHUNK_NEVER, and the callback returns 0. jpayne@68: jpayne@68: At this point, you can set up a callback function that will be jpayne@68: called after each row has been read, which you can use to control jpayne@68: a progress meter or the like. It's demonstrated in pngtest.c. jpayne@68: You must supply a function jpayne@68: jpayne@68: void read_row_callback(png_structp png_ptr, jpayne@68: png_uint_32 row, int pass) jpayne@68: { jpayne@68: /* put your code here */ jpayne@68: } jpayne@68: jpayne@68: (You can give it another name that you like instead of "read_row_callback") jpayne@68: jpayne@68: To inform libpng about your function, use jpayne@68: jpayne@68: png_set_read_status_fn(png_ptr, read_row_callback); jpayne@68: jpayne@68: When this function is called the row has already been completely processed and jpayne@68: the 'row' and 'pass' refer to the next row to be handled. For the jpayne@68: non-interlaced case the row that was just handled is simply one less than the jpayne@68: passed in row number, and pass will always be 0. For the interlaced case the jpayne@68: same applies unless the row value is 0, in which case the row just handled was jpayne@68: the last one from one of the preceding passes. Because interlacing may skip a jpayne@68: pass you cannot be sure that the preceding pass is just 'pass\-1'; if you really jpayne@68: need to know what the last pass is record (row,pass) from the callback and use jpayne@68: the last recorded value each time. jpayne@68: jpayne@68: As with the user transform you can find the output row using the jpayne@68: PNG_ROW_FROM_PASS_ROW macro. jpayne@68: jpayne@68: .SS Unknown-chunk handling jpayne@68: jpayne@68: Now you get to set the way the library processes unknown chunks in the jpayne@68: input PNG stream. Both known and unknown chunks will be read. Normal jpayne@68: behavior is that known chunks will be parsed into information in jpayne@68: various info_ptr members while unknown chunks will be discarded. This jpayne@68: behavior can be wasteful if your application will never use some known jpayne@68: chunk types. To change this, you can call: jpayne@68: jpayne@68: png_set_keep_unknown_chunks(png_ptr, keep, jpayne@68: chunk_list, num_chunks); jpayne@68: jpayne@68: keep - 0: default unknown chunk handling jpayne@68: 1: ignore; do not keep jpayne@68: 2: keep only if safe-to-copy jpayne@68: 3: keep even if unsafe-to-copy jpayne@68: jpayne@68: You can use these definitions: jpayne@68: PNG_HANDLE_CHUNK_AS_DEFAULT 0 jpayne@68: PNG_HANDLE_CHUNK_NEVER 1 jpayne@68: PNG_HANDLE_CHUNK_IF_SAFE 2 jpayne@68: PNG_HANDLE_CHUNK_ALWAYS 3 jpayne@68: jpayne@68: chunk_list - list of chunks affected (a byte string, jpayne@68: five bytes per chunk, NULL or '\0' if jpayne@68: num_chunks is positive; ignored if jpayne@68: numchunks <= 0). jpayne@68: jpayne@68: num_chunks - number of chunks affected; if 0, all jpayne@68: unknown chunks are affected. If positive, jpayne@68: only the chunks in the list are affected, jpayne@68: and if negative all unknown chunks and jpayne@68: all known chunks except for the IHDR, jpayne@68: PLTE, tRNS, IDAT, and IEND chunks are jpayne@68: affected. jpayne@68: jpayne@68: Unknown chunks declared in this way will be saved as raw data onto a jpayne@68: list of png_unknown_chunk structures. If a chunk that is normally jpayne@68: known to libpng is named in the list, it will be handled as unknown, jpayne@68: according to the "keep" directive. If a chunk is named in successive jpayne@68: instances of png_set_keep_unknown_chunks(), the final instance will jpayne@68: take precedence. The IHDR and IEND chunks should not be named in jpayne@68: chunk_list; if they are, libpng will process them normally anyway. jpayne@68: If you know that your application will never make use of some particular jpayne@68: chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below. jpayne@68: jpayne@68: Here is an example of the usage of png_set_keep_unknown_chunks(), jpayne@68: where the private "vpAg" chunk will later be processed by a user chunk jpayne@68: callback function: jpayne@68: jpayne@68: png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'}; jpayne@68: jpayne@68: #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED) jpayne@68: png_byte unused_chunks[]= jpayne@68: { jpayne@68: 104, 73, 83, 84, (png_byte) '\0', /* hIST */ jpayne@68: 105, 84, 88, 116, (png_byte) '\0', /* iTXt */ jpayne@68: 112, 67, 65, 76, (png_byte) '\0', /* pCAL */ jpayne@68: 115, 67, 65, 76, (png_byte) '\0', /* sCAL */ jpayne@68: 115, 80, 76, 84, (png_byte) '\0', /* sPLT */ jpayne@68: 116, 73, 77, 69, (png_byte) '\0', /* tIME */ jpayne@68: }; jpayne@68: #endif jpayne@68: jpayne@68: ... jpayne@68: jpayne@68: #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED) jpayne@68: /* ignore all unknown chunks jpayne@68: * (use global setting "2" for libpng16 and earlier): jpayne@68: */ jpayne@68: png_set_keep_unknown_chunks(read_ptr, 2, NULL, 0); jpayne@68: jpayne@68: /* except for vpAg: */ jpayne@68: png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1); jpayne@68: jpayne@68: /* also ignore unused known chunks: */ jpayne@68: png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks, jpayne@68: (int)(sizeof unused_chunks)/5); jpayne@68: #endif jpayne@68: jpayne@68: .SS User limits jpayne@68: jpayne@68: The PNG specification allows the width and height of an image to be as jpayne@68: large as 2^(31\-1 (0x7fffffff), or about 2.147 billion rows and columns. jpayne@68: For safety, libpng imposes a default limit of 1 million rows and columns. jpayne@68: Larger images will be rejected immediately with a png_error() call. If jpayne@68: you wish to change these limits, you can use jpayne@68: jpayne@68: png_set_user_limits(png_ptr, width_max, height_max); jpayne@68: jpayne@68: to set your own limits (libpng may reject some very wide images jpayne@68: anyway because of potential buffer overflow conditions). jpayne@68: jpayne@68: You should put this statement after you create the PNG structure and jpayne@68: before calling png_read_info(), png_read_png(), or png_process_data(). jpayne@68: jpayne@68: When writing a PNG datastream, put this statement before calling jpayne@68: png_write_info() or png_write_png(). jpayne@68: jpayne@68: If you need to retrieve the limits that are being applied, use jpayne@68: jpayne@68: width_max = png_get_user_width_max(png_ptr); jpayne@68: height_max = png_get_user_height_max(png_ptr); jpayne@68: jpayne@68: The PNG specification sets no limit on the number of ancillary chunks jpayne@68: allowed in a PNG datastream. By default, libpng imposes a limit of jpayne@68: a total of 1000 sPLT, tEXt, iTXt, zTXt, and unknown chunks to be stored. jpayne@68: If you have set up both info_ptr and end_info_ptr, the limit applies jpayne@68: separately to each. You can change the limit on the total number of such jpayne@68: chunks that will be stored, with jpayne@68: jpayne@68: png_set_chunk_cache_max(png_ptr, user_chunk_cache_max); jpayne@68: jpayne@68: where 0x7fffffffL means unlimited. You can retrieve this limit with jpayne@68: jpayne@68: chunk_cache_max = png_get_chunk_cache_max(png_ptr); jpayne@68: jpayne@68: Libpng imposes a limit of 8 Megabytes (8,000,000 bytes) on the amount of jpayne@68: memory that any chunk other than IDAT can occupy, originally or when jpayne@68: decompressed (prior to libpng-1.6.32 the limit was only applied to compressed jpayne@68: chunks after decompression). You can change this limit with jpayne@68: jpayne@68: png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max); jpayne@68: jpayne@68: and you can retrieve the limit with jpayne@68: jpayne@68: chunk_malloc_max = png_get_chunk_malloc_max(png_ptr); jpayne@68: jpayne@68: Any chunks that would cause either of these limits to be exceeded will jpayne@68: be ignored. jpayne@68: jpayne@68: .SS Information about your system jpayne@68: jpayne@68: If you intend to display the PNG or to incorporate it in other image data you jpayne@68: need to tell libpng information about your display or drawing surface so that jpayne@68: libpng can convert the values in the image to match the display. jpayne@68: jpayne@68: From libpng-1.5.4 this information can be set before reading the PNG file jpayne@68: header. In earlier versions png_set_gamma() existed but behaved incorrectly if jpayne@68: called before the PNG file header had been read and png_set_alpha_mode() did not jpayne@68: exist. jpayne@68: jpayne@68: If you need to support versions prior to libpng-1.5.4 test the version number jpayne@68: as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures jpayne@68: described in the appropriate manual page. jpayne@68: jpayne@68: You give libpng the encoding expected by your system expressed as a 'gamma' jpayne@68: value. You can also specify a default encoding for the PNG file in jpayne@68: case the required information is missing from the file. By default libpng jpayne@68: assumes that the PNG data matches your system, to keep this default call: jpayne@68: jpayne@68: png_set_gamma(png_ptr, screen_gamma, output_gamma); jpayne@68: jpayne@68: or you can use the fixed point equivalent: jpayne@68: jpayne@68: png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma, jpayne@68: PNG_FP_1*output_gamma); jpayne@68: jpayne@68: If you don't know the gamma for your system it is probably 2.2 - a good jpayne@68: approximation to the IEC standard for display systems (sRGB). If images are jpayne@68: too contrasty or washed out you got the value wrong - check your system jpayne@68: documentation! jpayne@68: jpayne@68: Many systems permit the system gamma to be changed via a lookup table in the jpayne@68: display driver, a few systems, including older Macs, change the response by jpayne@68: default. As of 1.5.4 three special values are available to handle common jpayne@68: situations: jpayne@68: jpayne@68: PNG_DEFAULT_sRGB: Indicates that the system conforms to the jpayne@68: IEC 61966-2-1 standard. This matches almost jpayne@68: all systems. jpayne@68: PNG_GAMMA_MAC_18: Indicates that the system is an older jpayne@68: (pre Mac OS 10.6) Apple Macintosh system with jpayne@68: the default settings. jpayne@68: PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates jpayne@68: that the system expects data with no gamma jpayne@68: encoding. jpayne@68: jpayne@68: You would use the linear (unencoded) value if you need to process the pixel jpayne@68: values further because this avoids the need to decode and re-encode each jpayne@68: component value whenever arithmetic is performed. A lot of graphics software jpayne@68: uses linear values for this reason, often with higher precision component values jpayne@68: to preserve overall accuracy. jpayne@68: jpayne@68: jpayne@68: The output_gamma value expresses how to decode the output values, not how jpayne@68: they are encoded. The values used correspond to the normal numbers used to jpayne@68: describe the overall gamma of a computer display system; for example 2.2 for jpayne@68: an sRGB conformant system. The values are scaled by 100000 in the _fixed jpayne@68: version of the API (so 220000 for sRGB.) jpayne@68: jpayne@68: The inverse of the value is always used to provide a default for the PNG file jpayne@68: encoding if it has no gAMA chunk and if png_set_gamma() has not been called jpayne@68: to override the PNG gamma information. jpayne@68: jpayne@68: When the ALPHA_OPTIMIZED mode is selected the output gamma is used to encode jpayne@68: opaque pixels however pixels with lower alpha values are not encoded, jpayne@68: regardless of the output gamma setting. jpayne@68: jpayne@68: When the standard Porter Duff handling is requested with mode 1 the output jpayne@68: encoding is set to be linear and the output_gamma value is only relevant jpayne@68: as a default for input data that has no gamma information. The linear output jpayne@68: encoding will be overridden if png_set_gamma() is called - the results may be jpayne@68: highly unexpected! jpayne@68: jpayne@68: The following numbers are derived from the sRGB standard and the research jpayne@68: behind it. sRGB is defined to be approximated by a PNG gAMA chunk value of jpayne@68: 0.45455 (1/2.2) for PNG. The value implicitly includes any viewing jpayne@68: correction required to take account of any differences in the color jpayne@68: environment of the original scene and the intended display environment; the jpayne@68: value expresses how to *decode* the image for display, not how the original jpayne@68: data was *encoded*. jpayne@68: jpayne@68: sRGB provides a peg for the PNG standard by defining a viewing environment. jpayne@68: sRGB itself, and earlier TV standards, actually use a more complex transform jpayne@68: (a linear portion then a gamma 2.4 power law) than PNG can express. (PNG is jpayne@68: limited to simple power laws.) By saying that an image for direct display on jpayne@68: an sRGB conformant system should be stored with a gAMA chunk value of 45455 jpayne@68: (11.3.3.2 and 11.3.3.5 of the ISO PNG specification) the PNG specification jpayne@68: makes it possible to derive values for other display systems and jpayne@68: environments. jpayne@68: jpayne@68: The Mac value is deduced from the sRGB based on an assumption that the actual jpayne@68: extra viewing correction used in early Mac display systems was implemented as jpayne@68: a power 1.45 lookup table. jpayne@68: jpayne@68: Any system where a programmable lookup table is used or where the behavior of jpayne@68: the final display device characteristics can be changed requires system jpayne@68: specific code to obtain the current characteristic. However this can be jpayne@68: difficult and most PNG gamma correction only requires an approximate value. jpayne@68: jpayne@68: By default, if png_set_alpha_mode() is not called, libpng assumes that all jpayne@68: values are unencoded, linear, values and that the output device also has a jpayne@68: linear characteristic. This is only very rarely correct - it is invariably jpayne@68: better to call png_set_alpha_mode() with PNG_DEFAULT_sRGB than rely on the jpayne@68: default if you don't know what the right answer is! jpayne@68: jpayne@68: The special value PNG_GAMMA_MAC_18 indicates an older Mac system (pre Mac OS jpayne@68: 10.6) which used a correction table to implement a somewhat lower gamma on an jpayne@68: otherwise sRGB system. jpayne@68: jpayne@68: Both these values are reserved (not simple gamma values) in order to allow jpayne@68: more precise correction internally in the future. jpayne@68: jpayne@68: NOTE: the values can be passed to either the fixed or floating jpayne@68: point APIs, but the floating point API will also accept floating point jpayne@68: values. jpayne@68: jpayne@68: The second thing you may need to tell libpng about is how your system handles jpayne@68: alpha channel information. Some, but not all, PNG files contain an alpha jpayne@68: channel. To display these files correctly you need to compose the data onto a jpayne@68: suitable background, as described in the PNG specification. jpayne@68: jpayne@68: Libpng only supports composing onto a single color (using png_set_background; jpayne@68: see below). Otherwise you must do the composition yourself and, in this case, jpayne@68: you may need to call png_set_alpha_mode: jpayne@68: jpayne@68: #if PNG_LIBPNG_VER >= 10504 jpayne@68: png_set_alpha_mode(png_ptr, mode, screen_gamma); jpayne@68: #else jpayne@68: png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma); jpayne@68: #endif jpayne@68: jpayne@68: The screen_gamma value is the same as the argument to png_set_gamma; however, jpayne@68: how it affects the output depends on the mode. png_set_alpha_mode() sets the jpayne@68: file gamma default to 1/screen_gamma, so normally you don't need to call jpayne@68: png_set_gamma. If you need different defaults call png_set_gamma() before jpayne@68: png_set_alpha_mode() - if you call it after it will override the settings made jpayne@68: by png_set_alpha_mode(). jpayne@68: jpayne@68: The mode is as follows: jpayne@68: jpayne@68: PNG_ALPHA_PNG: The data is encoded according to the PNG jpayne@68: specification. Red, green and blue, or gray, components are jpayne@68: gamma encoded color values and are not premultiplied by the jpayne@68: alpha value. The alpha value is a linear measure of the jpayne@68: contribution of the pixel to the corresponding final output pixel. jpayne@68: jpayne@68: You should normally use this format if you intend to perform jpayne@68: color correction on the color values; most, maybe all, color jpayne@68: correction software has no handling for the alpha channel and, jpayne@68: anyway, the math to handle pre-multiplied component values is jpayne@68: unnecessarily complex. jpayne@68: jpayne@68: Before you do any arithmetic on the component values you need jpayne@68: to remove the gamma encoding and multiply out the alpha jpayne@68: channel. See the PNG specification for more detail. It is jpayne@68: important to note that when an image with an alpha channel is jpayne@68: scaled, linear encoded, pre-multiplied component values must jpayne@68: be used! jpayne@68: jpayne@68: The remaining modes assume you don't need to do any further color correction or jpayne@68: that if you do, your color correction software knows all about alpha (it jpayne@68: probably doesn't!). They 'associate' the alpha with the color information by jpayne@68: storing color channel values that have been scaled by the alpha. The jpayne@68: advantage is that the color channels can be resampled (the image can be jpayne@68: scaled) in this form. The disadvantage is that normal practice is to store jpayne@68: linear, not (gamma) encoded, values and this requires 16-bit channels for jpayne@68: still images rather than the 8-bit channels that are just about sufficient if jpayne@68: gamma encoding is used. In addition all non-transparent pixel values, jpayne@68: including completely opaque ones, must be gamma encoded to produce the final jpayne@68: image. These are the 'STANDARD', 'ASSOCIATED' or 'PREMULTIPLIED' modes jpayne@68: described below (the latter being the two common names for associated alpha jpayne@68: color channels). Note that PNG files always contain non-associated color jpayne@68: channels; png_set_alpha_mode() with one of the modes causes the decoder to jpayne@68: convert the pixels to an associated form before returning them to your jpayne@68: application. jpayne@68: jpayne@68: Since it is not necessary to perform arithmetic on opaque color values so jpayne@68: long as they are not to be resampled and are in the final color space it is jpayne@68: possible to optimize the handling of alpha by storing the opaque pixels in jpayne@68: the PNG format (adjusted for the output color space) while storing partially jpayne@68: opaque pixels in the standard, linear, format. The accuracy required for jpayne@68: standard alpha composition is relatively low, because the pixels are jpayne@68: isolated, therefore typically the accuracy loss in storing 8-bit linear jpayne@68: values is acceptable. (This is not true if the alpha channel is used to jpayne@68: simulate transparency over large areas - use 16 bits or the PNG mode in jpayne@68: this case!) This is the 'OPTIMIZED' mode. For this mode a pixel is jpayne@68: treated as opaque only if the alpha value is equal to the maximum value. jpayne@68: jpayne@68: PNG_ALPHA_STANDARD: The data libpng produces is encoded in the jpayne@68: standard way assumed by most correctly written graphics software. jpayne@68: The gamma encoding will be removed by libpng and the jpayne@68: linear component values will be pre-multiplied by the jpayne@68: alpha channel. jpayne@68: jpayne@68: With this format the final image must be re-encoded to jpayne@68: match the display gamma before the image is displayed. jpayne@68: If your system doesn't do that, yet still seems to jpayne@68: perform arithmetic on the pixels without decoding them, jpayne@68: it is broken - check out the modes below. jpayne@68: jpayne@68: With PNG_ALPHA_STANDARD libpng always produces linear jpayne@68: component values, whatever screen_gamma you supply. The jpayne@68: screen_gamma value is, however, used as a default for jpayne@68: the file gamma if the PNG file has no gamma information. jpayne@68: jpayne@68: If you call png_set_gamma() after png_set_alpha_mode() you jpayne@68: will override the linear encoding. Instead the jpayne@68: pre-multiplied pixel values will be gamma encoded but jpayne@68: the alpha channel will still be linear. This may jpayne@68: actually match the requirements of some broken software, jpayne@68: but it is unlikely. jpayne@68: jpayne@68: While linear 8-bit data is often used it has jpayne@68: insufficient precision for any image with a reasonable jpayne@68: dynamic range. To avoid problems, and if your software jpayne@68: supports it, use png_set_expand_16() to force all jpayne@68: components to 16 bits. jpayne@68: jpayne@68: PNG_ALPHA_OPTIMIZED: This mode is the same as PNG_ALPHA_STANDARD jpayne@68: except that completely opaque pixels are gamma encoded according to jpayne@68: the screen_gamma value. Pixels with alpha less than 1.0 jpayne@68: will still have linear components. jpayne@68: jpayne@68: Use this format if you have control over your jpayne@68: compositing software and so don't do other arithmetic jpayne@68: (such as scaling) on the data you get from libpng. Your jpayne@68: compositing software can simply copy opaque pixels to jpayne@68: the output but still has linear values for the jpayne@68: non-opaque pixels. jpayne@68: jpayne@68: In normal compositing, where the alpha channel encodes jpayne@68: partial pixel coverage (as opposed to broad area jpayne@68: translucency), the inaccuracies of the 8-bit jpayne@68: representation of non-opaque pixels are irrelevant. jpayne@68: jpayne@68: You can also try this format if your software is broken; jpayne@68: it might look better. jpayne@68: jpayne@68: PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD; however, all component jpayne@68: values, including the alpha channel are gamma encoded. This is jpayne@68: broken because, in practice, no implementation that uses this choice jpayne@68: correctly undoes the encoding before handling alpha composition. Use this jpayne@68: choice only if other serious errors in the software or hardware you use jpayne@68: mandate it. In most cases of broken software or hardware the bug in the jpayne@68: final display manifests as a subtle halo around composited parts of the jpayne@68: image. You may not even perceive this as a halo; the composited part of jpayne@68: the image may simply appear separate from the background, as though it had jpayne@68: been cut out of paper and pasted on afterward. jpayne@68: jpayne@68: If you don't have to deal with bugs in software or hardware, or if you can fix jpayne@68: them, there are three recommended ways of using png_set_alpha_mode(): jpayne@68: jpayne@68: png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG, jpayne@68: screen_gamma); jpayne@68: jpayne@68: You can do color correction on the result (libpng does not currently jpayne@68: support color correction internally). When you handle the alpha channel jpayne@68: you need to undo the gamma encoding and multiply out the alpha. jpayne@68: jpayne@68: png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD, jpayne@68: screen_gamma); jpayne@68: png_set_expand_16(png_ptr); jpayne@68: jpayne@68: If you are using the high level interface, don't call png_set_expand_16(); jpayne@68: instead pass PNG_TRANSFORM_EXPAND_16 to the interface. jpayne@68: jpayne@68: With this mode you can't do color correction, but you can do arithmetic, jpayne@68: including composition and scaling, on the data without further processing. jpayne@68: jpayne@68: png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED, jpayne@68: screen_gamma); jpayne@68: jpayne@68: You can avoid the expansion to 16-bit components with this mode, but you jpayne@68: lose the ability to scale the image or perform other linear arithmetic. jpayne@68: All you can do is compose the result onto a matching output. Since this jpayne@68: mode is libpng-specific you also need to write your own composition jpayne@68: software. jpayne@68: jpayne@68: The following are examples of calls to png_set_alpha_mode to achieve the jpayne@68: required overall gamma correction and, where necessary, alpha jpayne@68: premultiplication. jpayne@68: jpayne@68: png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB); jpayne@68: jpayne@68: Choices for the alpha_mode are jpayne@68: jpayne@68: PNG_ALPHA_PNG 0 /* according to the PNG standard */ jpayne@68: PNG_ALPHA_STANDARD 1 /* according to Porter/Duff */ jpayne@68: PNG_ALPHA_ASSOCIATED 1 /* as above; this is the normal practice */ jpayne@68: PNG_ALPHA_PREMULTIPLIED 1 /* as above */ jpayne@68: PNG_ALPHA_OPTIMIZED 2 /* 'PNG' for opaque pixels, else 'STANDARD' */ jpayne@68: PNG_ALPHA_BROKEN 3 /* the alpha channel is gamma encoded */ jpayne@68: jpayne@68: PNG_ALPHA_PNG is the default libpng handling of the alpha channel. It is not jpayne@68: pre-multiplied into the color components. In addition the call states jpayne@68: that the output is for a sRGB system and causes all PNG files without gAMA jpayne@68: chunks to be assumed to be encoded using sRGB. jpayne@68: jpayne@68: png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC); jpayne@68: jpayne@68: In this case the output is assumed to be something like an sRGB conformant jpayne@68: display preceded by a power-law lookup table of power 1.45. This is how jpayne@68: early Mac systems behaved. jpayne@68: jpayne@68: png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_GAMMA_LINEAR); jpayne@68: jpayne@68: This is the classic Jim Blinn approach and will work in academic jpayne@68: environments where everything is done by the book. It has the shortcoming jpayne@68: of assuming that input PNG data with no gamma information is linear - this jpayne@68: is unlikely to be correct unless the PNG files were generated locally. jpayne@68: Most of the time the output precision will be so low as to show jpayne@68: significant banding in dark areas of the image. jpayne@68: jpayne@68: png_set_expand_16(pp); jpayne@68: png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_DEFAULT_sRGB); jpayne@68: jpayne@68: This is a somewhat more realistic Jim Blinn inspired approach. PNG files jpayne@68: are assumed to have the sRGB encoding if not marked with a gamma value and jpayne@68: the output is always 16 bits per component. This permits accurate scaling jpayne@68: and processing of the data. If you know that your input PNG files were jpayne@68: generated locally you might need to replace PNG_DEFAULT_sRGB with the jpayne@68: correct value for your system. jpayne@68: jpayne@68: png_set_alpha_mode(pp, PNG_ALPHA_OPTIMIZED, PNG_DEFAULT_sRGB); jpayne@68: jpayne@68: If you just need to composite the PNG image onto an existing background jpayne@68: and if you control the code that does this you can use the optimization jpayne@68: setting. In this case you just copy completely opaque pixels to the jpayne@68: output. For pixels that are not completely transparent (you just skip jpayne@68: those) you do the composition math using png_composite or png_composite_16 jpayne@68: below then encode the resultant 8-bit or 16-bit values to match the output jpayne@68: encoding. jpayne@68: jpayne@68: Other cases jpayne@68: jpayne@68: If neither the PNG nor the standard linear encoding work for you because jpayne@68: of the software or hardware you use then you have a big problem. The PNG jpayne@68: case will probably result in halos around the image. The linear encoding jpayne@68: will probably result in a washed out, too bright, image (it's actually too jpayne@68: contrasty.) Try the ALPHA_OPTIMIZED mode above - this will probably jpayne@68: substantially reduce the halos. Alternatively try: jpayne@68: jpayne@68: png_set_alpha_mode(pp, PNG_ALPHA_BROKEN, PNG_DEFAULT_sRGB); jpayne@68: jpayne@68: This option will also reduce the halos, but there will be slight dark jpayne@68: halos round the opaque parts of the image where the background is light. jpayne@68: In the OPTIMIZED mode the halos will be light halos where the background jpayne@68: is dark. Take your pick - the halos are unavoidable unless you can get jpayne@68: your hardware/software fixed! (The OPTIMIZED approach is slightly jpayne@68: faster.) jpayne@68: jpayne@68: When the default gamma of PNG files doesn't match the output gamma. jpayne@68: If you have PNG files with no gamma information png_set_alpha_mode allows jpayne@68: you to provide a default gamma, but it also sets the output gamma to the jpayne@68: matching value. If you know your PNG files have a gamma that doesn't jpayne@68: match the output you can take advantage of the fact that jpayne@68: png_set_alpha_mode always sets the output gamma but only sets the PNG jpayne@68: default if it is not already set: jpayne@68: jpayne@68: png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB); jpayne@68: png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC); jpayne@68: jpayne@68: The first call sets both the default and the output gamma values, the jpayne@68: second call overrides the output gamma without changing the default. This jpayne@68: is easier than achieving the same effect with png_set_gamma. You must use jpayne@68: PNG_ALPHA_PNG for the first call - internal checking in png_set_alpha will jpayne@68: fire if more than one call to png_set_alpha_mode and png_set_background is jpayne@68: made in the same read operation, however multiple calls with PNG_ALPHA_PNG jpayne@68: are ignored. jpayne@68: jpayne@68: If you don't need, or can't handle, the alpha channel you can call jpayne@68: png_set_background() to remove it by compositing against a fixed color. Don't jpayne@68: call png_set_strip_alpha() to do this - it will leave spurious pixel values in jpayne@68: transparent parts of this image. jpayne@68: jpayne@68: png_set_background(png_ptr, &background_color, jpayne@68: PNG_BACKGROUND_GAMMA_SCREEN, 0, 1); jpayne@68: jpayne@68: The background_color is an RGB or grayscale value according to the data format jpayne@68: libpng will produce for you. Because you don't yet know the format of the PNG jpayne@68: file, if you call png_set_background at this point you must arrange for the jpayne@68: format produced by libpng to always have 8-bit or 16-bit components and then jpayne@68: store the color as an 8-bit or 16-bit color as appropriate. The color contains jpayne@68: separate gray and RGB component values, so you can let libpng produce gray or jpayne@68: RGB output according to the input format, but low bit depth grayscale images jpayne@68: must always be converted to at least 8-bit format. (Even though low bit depth jpayne@68: grayscale images can't have an alpha channel they can have a transparent jpayne@68: color!) jpayne@68: jpayne@68: You set the transforms you need later, either as flags to the high level jpayne@68: interface or libpng API calls for the low level interface. For reference the jpayne@68: settings and API calls required are: jpayne@68: jpayne@68: 8-bit values: jpayne@68: PNG_TRANSFORM_SCALE_16 | PNG_EXPAND jpayne@68: png_set_expand(png_ptr); png_set_scale_16(png_ptr); jpayne@68: jpayne@68: If you must get exactly the same inaccurate results jpayne@68: produced by default in versions prior to libpng-1.5.4, jpayne@68: use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr) jpayne@68: instead. jpayne@68: jpayne@68: 16-bit values: jpayne@68: PNG_TRANSFORM_EXPAND_16 jpayne@68: png_set_expand_16(png_ptr); jpayne@68: jpayne@68: In either case palette image data will be expanded to RGB. If you just want jpayne@68: color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr) jpayne@68: to the list. jpayne@68: jpayne@68: Calling png_set_background before the PNG file header is read will not work jpayne@68: prior to libpng-1.5.4. Because the failure may result in unexpected warnings or jpayne@68: errors it is therefore much safer to call png_set_background after the head has jpayne@68: been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be jpayne@68: used with the high level interface. jpayne@68: jpayne@68: .SS The high-level read interface jpayne@68: jpayne@68: At this point there are two ways to proceed; through the high-level jpayne@68: read interface, or through a sequence of low-level read operations. jpayne@68: You can use the high-level interface if (a) you are willing to read jpayne@68: the entire image into memory, and (b) the input transformations jpayne@68: you want to do are limited to the following set: jpayne@68: jpayne@68: PNG_TRANSFORM_IDENTITY No transformation jpayne@68: PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to jpayne@68: 8-bit accurately jpayne@68: PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to jpayne@68: 8-bit less accurately jpayne@68: PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel jpayne@68: PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit jpayne@68: samples to bytes jpayne@68: PNG_TRANSFORM_PACKSWAP Change order of packed jpayne@68: pixels to LSB first jpayne@68: PNG_TRANSFORM_EXPAND Perform set_expand() jpayne@68: PNG_TRANSFORM_INVERT_MONO Invert monochrome images jpayne@68: PNG_TRANSFORM_SHIFT Normalize pixels to the jpayne@68: sBIT depth jpayne@68: PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA jpayne@68: to BGRA jpayne@68: PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA jpayne@68: to AG jpayne@68: PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity jpayne@68: to transparency jpayne@68: PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples jpayne@68: PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples jpayne@68: to RGB (or GA to RGBA) jpayne@68: PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits jpayne@68: jpayne@68: (This excludes setting a background color, doing gamma transformation, jpayne@68: quantizing, and setting filler.) If this is the case, simply do this: jpayne@68: jpayne@68: png_read_png(png_ptr, info_ptr, png_transforms, NULL) jpayne@68: jpayne@68: where png_transforms is an integer containing the bitwise OR of some jpayne@68: set of transformation flags. This call is equivalent to png_read_info(), jpayne@68: followed the set of transformations indicated by the transform mask, jpayne@68: then png_read_image(), and finally png_read_end(). jpayne@68: jpayne@68: (The final parameter of this call is not yet used. Someday it might point jpayne@68: to transformation parameters required by some future input transform.) jpayne@68: jpayne@68: You must use png_transforms and not call any png_set_transform() functions jpayne@68: when you use png_read_png(). jpayne@68: jpayne@68: After you have called png_read_png(), you can retrieve the image data jpayne@68: with jpayne@68: jpayne@68: row_pointers = png_get_rows(png_ptr, info_ptr); jpayne@68: jpayne@68: where row_pointers is an array of pointers to the pixel data for each row: jpayne@68: jpayne@68: png_bytep row_pointers[height]; jpayne@68: jpayne@68: If you know your image size and pixel size ahead of time, you can allocate jpayne@68: row_pointers prior to calling png_read_png() with jpayne@68: jpayne@68: if (height > PNG_UINT_32_MAX / (sizeof (png_bytep))) jpayne@68: png_error(png_ptr, jpayne@68: "Image is too tall to process in memory"); jpayne@68: jpayne@68: if (width > PNG_UINT_32_MAX / pixel_size) jpayne@68: png_error(png_ptr, jpayne@68: "Image is too wide to process in memory"); jpayne@68: jpayne@68: row_pointers = png_malloc(png_ptr, jpayne@68: height*(sizeof (png_bytep))); jpayne@68: jpayne@68: for (int i = 0; i < height, i++) jpayne@68: row_pointers[i] = NULL; /* security precaution */ jpayne@68: jpayne@68: for (int i = 0; i < height, i++) jpayne@68: row_pointers[i] = png_malloc(png_ptr, jpayne@68: width*pixel_size); jpayne@68: jpayne@68: png_set_rows(png_ptr, info_ptr, &row_pointers); jpayne@68: jpayne@68: Alternatively you could allocate your image in one big block and define jpayne@68: row_pointers[i] to point into the proper places in your block, but first jpayne@68: be sure that your platform is able to allocate such a large buffer: jpayne@68: jpayne@68: /* Guard against integer overflow */ jpayne@68: if (height > PNG_SIZE_MAX/(width*pixel_size)) jpayne@68: png_error(png_ptr, "image_data buffer would be too large"); jpayne@68: jpayne@68: png_bytep buffer = png_malloc(png_ptr, jpayne@68: height*width*pixel_size); jpayne@68: jpayne@68: for (int i = 0; i < height, i++) jpayne@68: row_pointers[i] = buffer + i*width*pixel_size; jpayne@68: jpayne@68: png_set_rows(png_ptr, info_ptr, &row_pointers); jpayne@68: jpayne@68: If you use png_set_rows(), the application is responsible for freeing jpayne@68: row_pointers (and row_pointers[i], if they were separately allocated). jpayne@68: jpayne@68: If you don't allocate row_pointers ahead of time, png_read_png() will jpayne@68: do it, and it'll be free'ed by libpng when you call png_destroy_*(). jpayne@68: jpayne@68: .SS The low-level read interface jpayne@68: jpayne@68: If you are going the low-level route, you are now ready to read all jpayne@68: the file information up to the actual image data. You do this with a jpayne@68: call to png_read_info(). jpayne@68: jpayne@68: png_read_info(png_ptr, info_ptr); jpayne@68: jpayne@68: This will process all chunks up to but not including the image data. jpayne@68: jpayne@68: This also copies some of the data from the PNG file into the decode structure jpayne@68: for use in later transformations. Important information copied in is: jpayne@68: jpayne@68: 1) The PNG file gamma from the gAMA chunk. This overwrites the default value jpayne@68: provided by an earlier call to png_set_gamma or png_set_alpha_mode. jpayne@68: jpayne@68: 2) Prior to libpng-1.5.4 the background color from a bKGd chunk. This jpayne@68: damages the information provided by an earlier call to png_set_background jpayne@68: resulting in unexpected behavior. Libpng-1.5.4 no longer does this. jpayne@68: jpayne@68: 3) The number of significant bits in each component value. Libpng uses this to jpayne@68: optimize gamma handling by reducing the internal lookup table sizes. jpayne@68: jpayne@68: 4) The transparent color information from a tRNS chunk. This can be modified by jpayne@68: a later call to png_set_tRNS. jpayne@68: jpayne@68: .SS Querying the info structure jpayne@68: jpayne@68: Functions are used to get the information from the info_ptr once it jpayne@68: has been read. Note that these fields may not be completely filled jpayne@68: in until png_read_end() has read the chunk data following the image. jpayne@68: jpayne@68: png_get_IHDR(png_ptr, info_ptr, &width, &height, jpayne@68: &bit_depth, &color_type, &interlace_type, jpayne@68: &compression_type, &filter_method); jpayne@68: jpayne@68: width - holds the width of the image jpayne@68: in pixels (up to 2^31). jpayne@68: jpayne@68: height - holds the height of the image jpayne@68: in pixels (up to 2^31). jpayne@68: jpayne@68: bit_depth - holds the bit depth of one of the jpayne@68: image channels. (valid values are jpayne@68: 1, 2, 4, 8, 16 and depend also on jpayne@68: the color_type. See also jpayne@68: significant bits (sBIT) below). jpayne@68: jpayne@68: color_type - describes which color/alpha channels jpayne@68: are present. jpayne@68: PNG_COLOR_TYPE_GRAY jpayne@68: (bit depths 1, 2, 4, 8, 16) jpayne@68: PNG_COLOR_TYPE_GRAY_ALPHA jpayne@68: (bit depths 8, 16) jpayne@68: PNG_COLOR_TYPE_PALETTE jpayne@68: (bit depths 1, 2, 4, 8) jpayne@68: PNG_COLOR_TYPE_RGB jpayne@68: (bit_depths 8, 16) jpayne@68: PNG_COLOR_TYPE_RGB_ALPHA jpayne@68: (bit_depths 8, 16) jpayne@68: jpayne@68: PNG_COLOR_MASK_PALETTE jpayne@68: PNG_COLOR_MASK_COLOR jpayne@68: PNG_COLOR_MASK_ALPHA jpayne@68: jpayne@68: interlace_type - (PNG_INTERLACE_NONE or jpayne@68: PNG_INTERLACE_ADAM7) jpayne@68: jpayne@68: compression_type - (must be PNG_COMPRESSION_TYPE_BASE jpayne@68: for PNG 1.0) jpayne@68: jpayne@68: filter_method - (must be PNG_FILTER_TYPE_BASE jpayne@68: for PNG 1.0, and can also be jpayne@68: PNG_INTRAPIXEL_DIFFERENCING if jpayne@68: the PNG datastream is embedded in jpayne@68: a MNG-1.0 datastream) jpayne@68: jpayne@68: Any of width, height, color_type, bit_depth, jpayne@68: interlace_type, compression_type, or filter_method can jpayne@68: be NULL if you are not interested in their values. jpayne@68: jpayne@68: Note that png_get_IHDR() returns 32-bit data into jpayne@68: the application's width and height variables. jpayne@68: This is an unsafe situation if these are not png_uint_32 jpayne@68: variables. In such situations, the jpayne@68: png_get_image_width() and png_get_image_height() jpayne@68: functions described below are safer. jpayne@68: jpayne@68: width = png_get_image_width(png_ptr, jpayne@68: info_ptr); jpayne@68: jpayne@68: height = png_get_image_height(png_ptr, jpayne@68: info_ptr); jpayne@68: jpayne@68: bit_depth = png_get_bit_depth(png_ptr, jpayne@68: info_ptr); jpayne@68: jpayne@68: color_type = png_get_color_type(png_ptr, jpayne@68: info_ptr); jpayne@68: jpayne@68: interlace_type = png_get_interlace_type(png_ptr, jpayne@68: info_ptr); jpayne@68: jpayne@68: compression_type = png_get_compression_type(png_ptr, jpayne@68: info_ptr); jpayne@68: jpayne@68: filter_method = png_get_filter_type(png_ptr, jpayne@68: info_ptr); jpayne@68: jpayne@68: channels = png_get_channels(png_ptr, info_ptr); jpayne@68: jpayne@68: channels - number of channels of info for the jpayne@68: color type (valid values are 1 (GRAY, jpayne@68: PALETTE), 2 (GRAY_ALPHA), 3 (RGB), jpayne@68: 4 (RGB_ALPHA or RGB + filler byte)) jpayne@68: jpayne@68: rowbytes = png_get_rowbytes(png_ptr, info_ptr); jpayne@68: jpayne@68: rowbytes - number of bytes needed to hold a row jpayne@68: This value, the bit_depth, color_type, jpayne@68: and the number of channels can change jpayne@68: if you use transforms such as jpayne@68: png_set_expand(). See jpayne@68: png_read_update_info(), below. jpayne@68: jpayne@68: signature = png_get_signature(png_ptr, info_ptr); jpayne@68: jpayne@68: signature - holds the signature read from the jpayne@68: file (if any). The data is kept in jpayne@68: the same offset it would be if the jpayne@68: whole signature were read (i.e. if an jpayne@68: application had already read in 4 jpayne@68: bytes of signature before starting jpayne@68: libpng, the remaining 4 bytes would jpayne@68: be in signature[4] through signature[7] jpayne@68: (see png_set_sig_bytes())). jpayne@68: jpayne@68: These are also important, but their validity depends on whether the chunk jpayne@68: has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_) and jpayne@68: png_get_(png_ptr, info_ptr, ...) functions return non-zero if the jpayne@68: data has been read, or zero if it is missing. The parameters to the jpayne@68: png_get_ are set directly if they are simple data types, or a jpayne@68: pointer into the info_ptr is returned for any complex types. jpayne@68: jpayne@68: The colorspace data from gAMA, cHRM, sRGB, iCCP, and sBIT chunks jpayne@68: is simply returned to give the application information about how the jpayne@68: image was encoded. Libpng itself only does transformations using the file jpayne@68: gamma when combining semitransparent pixels with the background color, and, jpayne@68: since libpng-1.6.0, when converting between 8-bit sRGB and 16-bit linear pixels jpayne@68: within the simplified API. Libpng also uses the file gamma when converting jpayne@68: RGB to gray, beginning with libpng-1.0.5, if the application calls jpayne@68: png_set_rgb_to_gray()). jpayne@68: jpayne@68: png_get_PLTE(png_ptr, info_ptr, &palette, jpayne@68: &num_palette); jpayne@68: jpayne@68: palette - the palette for the file jpayne@68: (array of png_color) jpayne@68: jpayne@68: num_palette - number of entries in the palette jpayne@68: jpayne@68: png_get_gAMA(png_ptr, info_ptr, &file_gamma); jpayne@68: png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma); jpayne@68: jpayne@68: file_gamma - the gamma at which the file is jpayne@68: written (PNG_INFO_gAMA) jpayne@68: jpayne@68: int_file_gamma - 100,000 times the gamma at which the jpayne@68: file is written jpayne@68: jpayne@68: png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x, jpayne@68: &red_y, &green_x, &green_y, &blue_x, &blue_y) jpayne@68: png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z, jpayne@68: &green_X, &green_Y, &green_Z, &blue_X, &blue_Y, jpayne@68: &blue_Z) jpayne@68: png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x, jpayne@68: &int_white_y, &int_red_x, &int_red_y, jpayne@68: &int_green_x, &int_green_y, &int_blue_x, jpayne@68: &int_blue_y) jpayne@68: png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y, jpayne@68: &int_red_Z, &int_green_X, &int_green_Y, jpayne@68: &int_green_Z, &int_blue_X, &int_blue_Y, jpayne@68: &int_blue_Z) jpayne@68: jpayne@68: {white,red,green,blue}_{x,y} jpayne@68: A color space encoding specified using the jpayne@68: chromaticities of the end points and the jpayne@68: white point. (PNG_INFO_cHRM) jpayne@68: jpayne@68: {red,green,blue}_{X,Y,Z} jpayne@68: A color space encoding specified using the jpayne@68: encoding end points - the CIE tristimulus jpayne@68: specification of the intended color of the red, jpayne@68: green and blue channels in the PNG RGB data. jpayne@68: The white point is simply the sum of the three jpayne@68: end points. (PNG_INFO_cHRM) jpayne@68: jpayne@68: png_get_sRGB(png_ptr, info_ptr, &srgb_intent); jpayne@68: jpayne@68: srgb_intent - the rendering intent (PNG_INFO_sRGB) jpayne@68: The presence of the sRGB chunk jpayne@68: means that the pixel data is in the jpayne@68: sRGB color space. This chunk also jpayne@68: implies specific values of gAMA and jpayne@68: cHRM. jpayne@68: jpayne@68: png_get_iCCP(png_ptr, info_ptr, &name, jpayne@68: &compression_type, &profile, &proflen); jpayne@68: jpayne@68: name - The profile name. jpayne@68: jpayne@68: compression_type - The compression type; always jpayne@68: PNG_COMPRESSION_TYPE_BASE for PNG 1.0. jpayne@68: You may give NULL to this argument to jpayne@68: ignore it. jpayne@68: jpayne@68: profile - International Color Consortium color jpayne@68: profile data. May contain NULs. jpayne@68: jpayne@68: proflen - length of profile data in bytes. jpayne@68: jpayne@68: png_get_sBIT(png_ptr, info_ptr, &sig_bit); jpayne@68: jpayne@68: sig_bit - the number of significant bits for jpayne@68: (PNG_INFO_sBIT) each of the gray, jpayne@68: red, green, and blue channels, jpayne@68: whichever are appropriate for the jpayne@68: given color type (png_color_16) jpayne@68: jpayne@68: png_get_tRNS(png_ptr, info_ptr, &trans_alpha, jpayne@68: &num_trans, &trans_color); jpayne@68: jpayne@68: trans_alpha - array of alpha (transparency) jpayne@68: entries for palette (PNG_INFO_tRNS) jpayne@68: jpayne@68: num_trans - number of transparent entries jpayne@68: (PNG_INFO_tRNS) jpayne@68: jpayne@68: trans_color - graylevel or color sample values of jpayne@68: the single transparent color for jpayne@68: non-paletted images (PNG_INFO_tRNS) jpayne@68: jpayne@68: png_get_eXIf_1(png_ptr, info_ptr, &num_exif, &exif); jpayne@68: jpayne@68: exif - Exif profile (array of png_byte) jpayne@68: (PNG_INFO_eXIf) jpayne@68: jpayne@68: png_get_hIST(png_ptr, info_ptr, &hist); jpayne@68: jpayne@68: hist - histogram of palette (array of jpayne@68: png_uint_16) (PNG_INFO_hIST) jpayne@68: jpayne@68: png_get_tIME(png_ptr, info_ptr, &mod_time); jpayne@68: jpayne@68: mod_time - time image was last modified jpayne@68: (PNG_INFO_tIME) jpayne@68: jpayne@68: png_get_bKGD(png_ptr, info_ptr, &background); jpayne@68: jpayne@68: background - background color (of type jpayne@68: png_color_16p) (PNG_INFO_bKGD) jpayne@68: valid 16-bit red, green and blue jpayne@68: values, regardless of color_type jpayne@68: jpayne@68: num_comments = png_get_text(png_ptr, info_ptr, jpayne@68: &text_ptr, &num_text); jpayne@68: jpayne@68: num_comments - number of comments jpayne@68: jpayne@68: text_ptr - array of png_text holding image jpayne@68: comments jpayne@68: jpayne@68: text_ptr[i].compression - type of compression used jpayne@68: on "text" PNG_TEXT_COMPRESSION_NONE jpayne@68: PNG_TEXT_COMPRESSION_zTXt jpayne@68: PNG_ITXT_COMPRESSION_NONE jpayne@68: PNG_ITXT_COMPRESSION_zTXt jpayne@68: jpayne@68: text_ptr[i].key - keyword for comment. Must contain jpayne@68: 1-79 characters. jpayne@68: jpayne@68: text_ptr[i].text - text comments for current jpayne@68: keyword. Can be empty. jpayne@68: jpayne@68: text_ptr[i].text_length - length of text string, jpayne@68: after decompression, 0 for iTXt jpayne@68: jpayne@68: text_ptr[i].itxt_length - length of itxt string, jpayne@68: after decompression, 0 for tEXt/zTXt jpayne@68: jpayne@68: text_ptr[i].lang - language of comment (empty jpayne@68: string for unknown). jpayne@68: jpayne@68: text_ptr[i].lang_key - keyword in UTF-8 jpayne@68: (empty string for unknown). jpayne@68: jpayne@68: Note that the itxt_length, lang, and lang_key jpayne@68: members of the text_ptr structure only exist when the jpayne@68: library is built with iTXt chunk support. Prior to jpayne@68: libpng-1.4.0 the library was built by default without jpayne@68: iTXt support. Also note that when iTXt is supported, jpayne@68: they contain NULL pointers when the "compression" jpayne@68: field contains PNG_TEXT_COMPRESSION_NONE or jpayne@68: PNG_TEXT_COMPRESSION_zTXt. jpayne@68: jpayne@68: num_text - number of comments (same as jpayne@68: num_comments; you can put NULL here jpayne@68: to avoid the duplication) jpayne@68: jpayne@68: Note while png_set_text() will accept text, language, jpayne@68: and translated keywords that can be NULL pointers, the jpayne@68: structure returned by png_get_text will always contain jpayne@68: regular zero-terminated C strings. They might be jpayne@68: empty strings but they will never be NULL pointers. jpayne@68: jpayne@68: num_spalettes = png_get_sPLT(png_ptr, info_ptr, jpayne@68: &palette_ptr); jpayne@68: jpayne@68: num_spalettes - number of sPLT chunks read. jpayne@68: jpayne@68: palette_ptr - array of palette structures holding jpayne@68: contents of one or more sPLT chunks jpayne@68: read. jpayne@68: jpayne@68: png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y, jpayne@68: &unit_type); jpayne@68: jpayne@68: offset_x - positive offset from the left edge jpayne@68: of the screen (can be negative) jpayne@68: jpayne@68: offset_y - positive offset from the top edge jpayne@68: of the screen (can be negative) jpayne@68: jpayne@68: unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER jpayne@68: jpayne@68: png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y, jpayne@68: &unit_type); jpayne@68: jpayne@68: res_x - pixels/unit physical resolution in jpayne@68: x direction jpayne@68: jpayne@68: res_y - pixels/unit physical resolution in jpayne@68: x direction jpayne@68: jpayne@68: unit_type - PNG_RESOLUTION_UNKNOWN, jpayne@68: PNG_RESOLUTION_METER jpayne@68: jpayne@68: png_get_sCAL(png_ptr, info_ptr, &unit, &width, jpayne@68: &height) jpayne@68: jpayne@68: unit - physical scale units (an integer) jpayne@68: jpayne@68: width - width of a pixel in physical scale units jpayne@68: jpayne@68: height - height of a pixel in physical scale units jpayne@68: (width and height are doubles) jpayne@68: jpayne@68: png_get_sCAL_s(png_ptr, info_ptr, &unit, &width, jpayne@68: &height) jpayne@68: jpayne@68: unit - physical scale units (an integer) jpayne@68: jpayne@68: width - width of a pixel in physical scale units jpayne@68: (expressed as a string) jpayne@68: jpayne@68: height - height of a pixel in physical scale units jpayne@68: (width and height are strings like "2.54") jpayne@68: jpayne@68: num_unknown_chunks = png_get_unknown_chunks(png_ptr, jpayne@68: info_ptr, &unknowns) jpayne@68: jpayne@68: unknowns - array of png_unknown_chunk jpayne@68: structures holding unknown chunks jpayne@68: jpayne@68: unknowns[i].name - name of unknown chunk jpayne@68: jpayne@68: unknowns[i].data - data of unknown chunk jpayne@68: jpayne@68: unknowns[i].size - size of unknown chunk's data jpayne@68: jpayne@68: unknowns[i].location - position of chunk in file jpayne@68: jpayne@68: The value of "i" corresponds to the order in which the jpayne@68: chunks were read from the PNG file or inserted with the jpayne@68: png_set_unknown_chunks() function. jpayne@68: jpayne@68: The value of "location" is a bitwise "or" of jpayne@68: jpayne@68: PNG_HAVE_IHDR (0x01) jpayne@68: PNG_HAVE_PLTE (0x02) jpayne@68: PNG_AFTER_IDAT (0x08) jpayne@68: jpayne@68: The data from the pHYs chunk can be retrieved in several convenient jpayne@68: forms: jpayne@68: jpayne@68: res_x = png_get_x_pixels_per_meter(png_ptr, jpayne@68: info_ptr) jpayne@68: jpayne@68: res_y = png_get_y_pixels_per_meter(png_ptr, jpayne@68: info_ptr) jpayne@68: jpayne@68: res_x_and_y = png_get_pixels_per_meter(png_ptr, jpayne@68: info_ptr) jpayne@68: jpayne@68: res_x = png_get_x_pixels_per_inch(png_ptr, jpayne@68: info_ptr) jpayne@68: jpayne@68: res_y = png_get_y_pixels_per_inch(png_ptr, jpayne@68: info_ptr) jpayne@68: jpayne@68: res_x_and_y = png_get_pixels_per_inch(png_ptr, jpayne@68: info_ptr) jpayne@68: jpayne@68: aspect_ratio = png_get_pixel_aspect_ratio(png_ptr, jpayne@68: info_ptr) jpayne@68: jpayne@68: Each of these returns 0 [signifying "unknown"] if jpayne@68: the data is not present or if res_x is 0; jpayne@68: res_x_and_y is 0 if res_x != res_y jpayne@68: jpayne@68: Note that because of the way the resolutions are jpayne@68: stored internally, the inch conversions won't jpayne@68: come out to exactly even number. For example, jpayne@68: 72 dpi is stored as 0.28346 pixels/meter, and jpayne@68: when this is retrieved it is 71.9988 dpi, so jpayne@68: be sure to round the returned value appropriately jpayne@68: if you want to display a reasonable-looking result. jpayne@68: jpayne@68: The data from the oFFs chunk can be retrieved in several convenient jpayne@68: forms: jpayne@68: jpayne@68: x_offset = png_get_x_offset_microns(png_ptr, info_ptr); jpayne@68: jpayne@68: y_offset = png_get_y_offset_microns(png_ptr, info_ptr); jpayne@68: jpayne@68: x_offset = png_get_x_offset_inches(png_ptr, info_ptr); jpayne@68: jpayne@68: y_offset = png_get_y_offset_inches(png_ptr, info_ptr); jpayne@68: jpayne@68: Each of these returns 0 [signifying "unknown" if both jpayne@68: x and y are 0] if the data is not present or if the jpayne@68: chunk is present but the unit is the pixel. The jpayne@68: remark about inexact inch conversions applies here jpayne@68: as well, because a value in inches can't always be jpayne@68: converted to microns and back without some loss jpayne@68: of precision. jpayne@68: jpayne@68: For more information, see the jpayne@68: PNG specification for chunk contents. Be careful with trusting jpayne@68: rowbytes, as some of the transformations could increase the space jpayne@68: needed to hold a row (expand, filler, gray_to_rgb, etc.). jpayne@68: See png_read_update_info(), below. jpayne@68: jpayne@68: A quick word about text_ptr and num_text. PNG stores comments in jpayne@68: keyword/text pairs, one pair per chunk, with no limit on the number jpayne@68: of text chunks, and a 2^31 byte limit on their size. While there are jpayne@68: suggested keywords, there is no requirement to restrict the use to these jpayne@68: strings. It is strongly suggested that keywords and text be sensible jpayne@68: to humans (that's the point), so don't use abbreviations. Non-printing jpayne@68: symbols are not allowed. See the PNG specification for more details. jpayne@68: There is also no requirement to have text after the keyword. jpayne@68: jpayne@68: Keywords should be limited to 79 Latin-1 characters without leading or jpayne@68: trailing spaces, but non-consecutive spaces are allowed within the jpayne@68: keyword. It is possible to have the same keyword any number of times. jpayne@68: The text_ptr is an array of png_text structures, each holding a jpayne@68: pointer to a language string, a pointer to a keyword and a pointer to jpayne@68: a text string. The text string, language code, and translated jpayne@68: keyword may be empty or NULL pointers. The keyword/text jpayne@68: pairs are put into the array in the order that they are received. jpayne@68: However, some or all of the text chunks may be after the image, so, to jpayne@68: make sure you have read all the text chunks, don't mess with these jpayne@68: until after you read the stuff after the image. This will be jpayne@68: mentioned again below in the discussion that goes with png_read_end(). jpayne@68: jpayne@68: .SS Input transformations jpayne@68: jpayne@68: After you've read the header information, you can set up the library jpayne@68: to handle any special transformations of the image data. The various jpayne@68: ways to transform the data will be described in the order that they jpayne@68: should occur. This is important, as some of these change the color jpayne@68: type and/or bit depth of the data, and some others only work on jpayne@68: certain color types and bit depths. jpayne@68: jpayne@68: Transformations you request are ignored if they don't have any meaning for a jpayne@68: particular input data format. However some transformations can have an effect jpayne@68: as a result of a previous transformation. If you specify a contradictory set of jpayne@68: transformations, for example both adding and removing the alpha channel, you jpayne@68: cannot predict the final result. jpayne@68: jpayne@68: The color used for the transparency values should be supplied in the same jpayne@68: format/depth as the current image data. It is stored in the same format/depth jpayne@68: as the image data in a tRNS chunk, so this is what libpng expects for this data. jpayne@68: jpayne@68: The color used for the background value depends on the need_expand argument as jpayne@68: described below. jpayne@68: jpayne@68: Data will be decoded into the supplied row buffers packed into bytes jpayne@68: unless the library has been told to transform it into another format. jpayne@68: For example, 4 bit/pixel paletted or grayscale data will be returned jpayne@68: 2 pixels/byte with the leftmost pixel in the high-order bits of the byte, jpayne@68: unless png_set_packing() is called. 8-bit RGB data will be stored jpayne@68: in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha() jpayne@68: is called to insert filler bytes, either before or after each RGB triplet. jpayne@68: jpayne@68: 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant jpayne@68: byte of the color value first, unless png_set_scale_16() is called to jpayne@68: transform it to regular RGB RGB triplets, or png_set_filler() or jpayne@68: png_set_add alpha() is called to insert two filler bytes, either before jpayne@68: or after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can jpayne@68: be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(), jpayne@68: or png_set_scale_16(). jpayne@68: jpayne@68: The following code transforms grayscale images of less than 8 to 8 bits, jpayne@68: changes paletted images to RGB, and adds a full alpha channel if there is jpayne@68: transparency information in a tRNS chunk. This is most useful on jpayne@68: grayscale images with bit depths of 2 or 4 or if there is a multiple-image jpayne@68: viewing application that wishes to treat all images in the same way. jpayne@68: jpayne@68: if (color_type == PNG_COLOR_TYPE_PALETTE) jpayne@68: png_set_palette_to_rgb(png_ptr); jpayne@68: jpayne@68: if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)) jpayne@68: png_set_tRNS_to_alpha(png_ptr); jpayne@68: jpayne@68: if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8) jpayne@68: png_set_expand_gray_1_2_4_to_8(png_ptr); jpayne@68: jpayne@68: The first two functions are actually aliases for png_set_expand(), added jpayne@68: in libpng version 1.0.4, with the function names expanded to improve code jpayne@68: readability. In some future version they may actually do different jpayne@68: things. jpayne@68: jpayne@68: As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was jpayne@68: added. It expands the sample depth without changing tRNS to alpha. jpayne@68: jpayne@68: As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as jpayne@68: png_set_expand(); however, the resultant channels have 16 bits rather than 8. jpayne@68: Use this when the output color or gray channels are made linear to avoid fairly jpayne@68: severe accuracy loss. jpayne@68: jpayne@68: if (bit_depth < 16) jpayne@68: png_set_expand_16(png_ptr); jpayne@68: jpayne@68: PNG can have files with 16 bits per channel. If you only can handle jpayne@68: 8 bits per channel, this will strip the pixels down to 8-bit. jpayne@68: jpayne@68: if (bit_depth == 16) jpayne@68: { jpayne@68: #if PNG_LIBPNG_VER >= 10504 jpayne@68: png_set_scale_16(png_ptr); jpayne@68: #else jpayne@68: png_set_strip_16(png_ptr); jpayne@68: #endif jpayne@68: } jpayne@68: jpayne@68: (The more accurate "png_set_scale_16()" API became available in libpng version jpayne@68: 1.5.4). jpayne@68: jpayne@68: If you need to process the alpha channel on the image separately from the image jpayne@68: data (for example if you convert it to a bitmap mask) it is possible to have jpayne@68: libpng strip the channel leaving just RGB or gray data: jpayne@68: jpayne@68: if (color_type & PNG_COLOR_MASK_ALPHA) jpayne@68: png_set_strip_alpha(png_ptr); jpayne@68: jpayne@68: If you strip the alpha channel you need to find some other way of dealing with jpayne@68: the information. If, instead, you want to convert the image to an opaque jpayne@68: version with no alpha channel use png_set_background; see below. jpayne@68: jpayne@68: As of libpng version 1.5.2, almost all useful expansions are supported, the jpayne@68: major omissions are conversion of grayscale to indexed images (which can be jpayne@68: done trivially in the application) and conversion of indexed to grayscale (which jpayne@68: can be done by a trivial manipulation of the palette.) jpayne@68: jpayne@68: In the following table, the 01 means grayscale with depth<8, 31 means jpayne@68: indexed with depth<8, other numerals represent the color type, "T" means jpayne@68: the tRNS chunk is present, A means an alpha channel is present, and O jpayne@68: means tRNS or alpha is present but all pixels in the image are opaque. jpayne@68: jpayne@68: FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O jpayne@68: TO jpayne@68: 01 - [G] - - - - - - - - - - - - - jpayne@68: 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q jpayne@68: 0 1 G + . . G G G G G G B B GB GB jpayne@68: 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt jpayne@68: 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt jpayne@68: 2 C P C C C + . . C - - CB CB B B jpayne@68: 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt jpayne@68: 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt jpayne@68: 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q jpayne@68: 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt jpayne@68: 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt jpayne@68: 4A lA G A T T GA GT GT GA GT GT + BA G GBA jpayne@68: 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G jpayne@68: 6A CA PA CA C C A T tT PA P P C CBA + BA jpayne@68: 6O CA PBA CA C C A tT T PA P P CBA C BA + jpayne@68: jpayne@68: Within the matrix, jpayne@68: "+" identifies entries where 'from' and 'to' are the same. jpayne@68: "-" means the transformation is not supported. jpayne@68: "." means nothing is necessary (a tRNS chunk can just be ignored). jpayne@68: "t" means the transformation is obtained by png_set_tRNS. jpayne@68: "A" means the transformation is obtained by png_set_add_alpha(). jpayne@68: "X" means the transformation is obtained by png_set_expand(). jpayne@68: "1" means the transformation is obtained by jpayne@68: png_set_expand_gray_1_2_4_to_8() (and by png_set_expand() jpayne@68: if there is no transparency in the original or the final jpayne@68: format). jpayne@68: "C" means the transformation is obtained by png_set_gray_to_rgb(). jpayne@68: "G" means the transformation is obtained by png_set_rgb_to_gray(). jpayne@68: "P" means the transformation is obtained by jpayne@68: png_set_expand_palette_to_rgb(). jpayne@68: "p" means the transformation is obtained by png_set_packing(). jpayne@68: "Q" means the transformation is obtained by png_set_quantize(). jpayne@68: "T" means the transformation is obtained by jpayne@68: png_set_tRNS_to_alpha(). jpayne@68: "B" means the transformation is obtained by jpayne@68: png_set_background(), or png_strip_alpha(). jpayne@68: jpayne@68: When an entry has multiple transforms listed all are required to cause the jpayne@68: right overall transformation. When two transforms are separated by a comma jpayne@68: either will do the job. When transforms are enclosed in [] the transform should jpayne@68: do the job but this is currently unimplemented - a different format will result jpayne@68: if the suggested transformations are used. jpayne@68: jpayne@68: In PNG files, the alpha channel in an image jpayne@68: is the level of opacity. If you need the alpha channel in an image to jpayne@68: be the level of transparency instead of opacity, you can invert the jpayne@68: alpha channel (or the tRNS chunk data) after it's read, so that 0 is jpayne@68: fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit jpayne@68: images) is fully transparent, with jpayne@68: jpayne@68: png_set_invert_alpha(png_ptr); jpayne@68: jpayne@68: PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as jpayne@68: they can, resulting in, for example, 8 pixels per byte for 1 bit jpayne@68: files. This code expands to 1 pixel per byte without changing the jpayne@68: values of the pixels: jpayne@68: jpayne@68: if (bit_depth < 8) jpayne@68: png_set_packing(png_ptr); jpayne@68: jpayne@68: PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels jpayne@68: stored in a PNG image have been "scaled" or "shifted" up to the next jpayne@68: higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] jpayne@68: to 8 bits/sample in the range [0, 255]). However, it is also possible jpayne@68: to convert the PNG pixel data back to the original bit depth of the jpayne@68: image. This call reduces the pixels back down to the original bit depth: jpayne@68: jpayne@68: png_color_8p sig_bit; jpayne@68: jpayne@68: if (png_get_sBIT(png_ptr, info_ptr, &sig_bit)) jpayne@68: png_set_shift(png_ptr, sig_bit); jpayne@68: jpayne@68: PNG files store 3-color pixels in red, green, blue order. This code jpayne@68: changes the storage of the pixels to blue, green, red: jpayne@68: jpayne@68: if (color_type == PNG_COLOR_TYPE_RGB || jpayne@68: color_type == PNG_COLOR_TYPE_RGB_ALPHA) jpayne@68: png_set_bgr(png_ptr); jpayne@68: jpayne@68: PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them jpayne@68: into 4 or 8 bytes for windowing systems that need them in this format: jpayne@68: jpayne@68: if (color_type == PNG_COLOR_TYPE_RGB) jpayne@68: png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE); jpayne@68: jpayne@68: where "filler" is the 8-bit or 16-bit number to fill with, and the location jpayne@68: is either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether jpayne@68: you want the filler before the RGB or after. When filling an 8-bit pixel, jpayne@68: the least significant 8 bits of the number are used, if a 16-bit number is jpayne@68: supplied. This transformation does not affect images that already have full jpayne@68: alpha channels. To add an opaque alpha channel, use filler=0xffff and jpayne@68: PNG_FILLER_AFTER which will generate RGBA pixels. jpayne@68: jpayne@68: Note that png_set_filler() does not change the color type. If you want jpayne@68: to do that, you can add a true alpha channel with jpayne@68: jpayne@68: if (color_type == PNG_COLOR_TYPE_RGB || jpayne@68: color_type == PNG_COLOR_TYPE_GRAY) jpayne@68: png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER); jpayne@68: jpayne@68: where "filler" contains the alpha value to assign to each pixel. jpayne@68: The png_set_add_alpha() function was added in libpng-1.2.7. jpayne@68: jpayne@68: If you are reading an image with an alpha channel, and you need the jpayne@68: data as ARGB instead of the normal PNG format RGBA: jpayne@68: jpayne@68: if (color_type == PNG_COLOR_TYPE_RGB_ALPHA) jpayne@68: png_set_swap_alpha(png_ptr); jpayne@68: jpayne@68: For some uses, you may want a grayscale image to be represented as jpayne@68: RGB. This code will do that conversion: jpayne@68: jpayne@68: if (color_type == PNG_COLOR_TYPE_GRAY || jpayne@68: color_type == PNG_COLOR_TYPE_GRAY_ALPHA) jpayne@68: png_set_gray_to_rgb(png_ptr); jpayne@68: jpayne@68: Conversely, you can convert an RGB or RGBA image to grayscale or grayscale jpayne@68: with alpha. jpayne@68: jpayne@68: if (color_type == PNG_COLOR_TYPE_RGB || jpayne@68: color_type == PNG_COLOR_TYPE_RGB_ALPHA) jpayne@68: png_set_rgb_to_gray(png_ptr, error_action, jpayne@68: (double)red_weight, (double)green_weight); jpayne@68: jpayne@68: error_action = 1: silently do the conversion jpayne@68: jpayne@68: error_action = 2: issue a warning if the original jpayne@68: image has any pixel where jpayne@68: red != green or red != blue jpayne@68: jpayne@68: error_action = 3: issue an error and abort the jpayne@68: conversion if the original jpayne@68: image has any pixel where jpayne@68: red != green or red != blue jpayne@68: jpayne@68: red_weight: weight of red component jpayne@68: jpayne@68: green_weight: weight of green component jpayne@68: If either weight is negative, default jpayne@68: weights are used. jpayne@68: jpayne@68: In the corresponding fixed point API the red_weight and green_weight values are jpayne@68: simply scaled by 100,000: jpayne@68: jpayne@68: png_set_rgb_to_gray(png_ptr, error_action, jpayne@68: (png_fixed_point)red_weight, jpayne@68: (png_fixed_point)green_weight); jpayne@68: jpayne@68: If you have set error_action = 1 or 2, you can jpayne@68: later check whether the image really was gray, after processing jpayne@68: the image rows, with the png_get_rgb_to_gray_status(png_ptr) function. jpayne@68: It will return a png_byte that is zero if the image was gray or jpayne@68: 1 if there were any non-gray pixels. Background and sBIT data jpayne@68: will be silently converted to grayscale, using the green channel jpayne@68: data for sBIT, regardless of the error_action setting. jpayne@68: jpayne@68: The default values come from the PNG file cHRM chunk if present; otherwise, the jpayne@68: defaults correspond to the ITU-R recommendation 709, and also the sRGB color jpayne@68: space, as recommended in the Charles Poynton's Colour FAQ, jpayne@68: Copyright (c) 2006-11-28 Charles Poynton, in section 9: jpayne@68: jpayne@68: jpayne@68: jpayne@68: Y = 0.2126 * R + 0.7152 * G + 0.0722 * B jpayne@68: jpayne@68: Previous versions of this document, 1998 through 2002, recommended a slightly jpayne@68: different formula: jpayne@68: jpayne@68: Y = 0.212671 * R + 0.715160 * G + 0.072169 * B jpayne@68: jpayne@68: Libpng uses an integer approximation: jpayne@68: jpayne@68: Y = (6968 * R + 23434 * G + 2366 * B)/32768 jpayne@68: jpayne@68: The calculation is done in a linear colorspace, if the image gamma jpayne@68: can be determined. jpayne@68: jpayne@68: The png_set_background() function has been described already; it tells libpng to jpayne@68: composite images with alpha or simple transparency against the supplied jpayne@68: background color. For compatibility with versions of libpng earlier than jpayne@68: libpng-1.5.4 it is recommended that you call the function after reading the file jpayne@68: header, even if you don't want to use the color in a bKGD chunk, if one exists. jpayne@68: jpayne@68: If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid), jpayne@68: you may use this color, or supply another color more suitable for jpayne@68: the current display (e.g., the background color from a web page). You jpayne@68: need to tell libpng how the color is represented, both the format of the jpayne@68: component values in the color (the number of bits) and the gamma encoding of the jpayne@68: color. The function takes two arguments, background_gamma_mode and need_expand jpayne@68: to convey this information; however, only two combinations are likely to be jpayne@68: useful: jpayne@68: jpayne@68: png_color_16 my_background; jpayne@68: png_color_16p image_background; jpayne@68: jpayne@68: if (png_get_bKGD(png_ptr, info_ptr, &image_background)) jpayne@68: png_set_background(png_ptr, image_background, jpayne@68: PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1); jpayne@68: else jpayne@68: png_set_background(png_ptr, &my_background, jpayne@68: PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1); jpayne@68: jpayne@68: The second call was described above - my_background is in the format of the jpayne@68: final, display, output produced by libpng. Because you now know the format of jpayne@68: the PNG it is possible to avoid the need to choose either 8-bit or 16-bit jpayne@68: output and to retain palette images (the palette colors will be modified jpayne@68: appropriately and the tRNS chunk removed.) However, if you are doing this, jpayne@68: take great care not to ask for transformations without checking first that jpayne@68: they apply! jpayne@68: jpayne@68: In the first call the background color has the original bit depth and color type jpayne@68: of the PNG file. So, for palette images the color is supplied as a palette jpayne@68: index and for low bit greyscale images the color is a reduced bit value in jpayne@68: image_background->gray. jpayne@68: jpayne@68: If you didn't call png_set_gamma() before reading the file header, for example jpayne@68: if you need your code to remain compatible with older versions of libpng prior jpayne@68: to libpng-1.5.4, this is the place to call it. jpayne@68: jpayne@68: Do not call it if you called png_set_alpha_mode(); doing so will damage the jpayne@68: settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is jpayne@68: supported then you can certainly do png_set_gamma() before reading the PNG jpayne@68: header.) jpayne@68: jpayne@68: This API unconditionally sets the screen and file gamma values, so it will jpayne@68: override the value in the PNG file unless it is called before the PNG file jpayne@68: reading starts. For this reason you must always call it with the PNG file jpayne@68: value when you call it in this position: jpayne@68: jpayne@68: if (png_get_gAMA(png_ptr, info_ptr, &file_gamma)) jpayne@68: png_set_gamma(png_ptr, screen_gamma, file_gamma); jpayne@68: jpayne@68: else jpayne@68: png_set_gamma(png_ptr, screen_gamma, 0.45455); jpayne@68: jpayne@68: If you need to reduce an RGB file to a paletted file, or if a paletted jpayne@68: file has more entries than will fit on your screen, png_set_quantize() jpayne@68: will do that. Note that this is a simple match quantization that merely jpayne@68: finds the closest color available. This should work fairly well with jpayne@68: optimized palettes, but fairly badly with linear color cubes. If you jpayne@68: pass a palette that is larger than maximum_colors, the file will jpayne@68: reduce the number of colors in the palette so it will fit into jpayne@68: maximum_colors. If there is a histogram, libpng will use it to make jpayne@68: more intelligent choices when reducing the palette. If there is no jpayne@68: histogram, it may not do as good a job. jpayne@68: jpayne@68: if (color_type & PNG_COLOR_MASK_COLOR) jpayne@68: { jpayne@68: if (png_get_valid(png_ptr, info_ptr, jpayne@68: PNG_INFO_PLTE)) jpayne@68: { jpayne@68: png_uint_16p histogram = NULL; jpayne@68: jpayne@68: png_get_hIST(png_ptr, info_ptr, jpayne@68: &histogram); jpayne@68: png_set_quantize(png_ptr, palette, num_palette, jpayne@68: max_screen_colors, histogram, 1); jpayne@68: } jpayne@68: jpayne@68: else jpayne@68: { jpayne@68: png_color std_color_cube[MAX_SCREEN_COLORS] = jpayne@68: { ... colors ... }; jpayne@68: jpayne@68: png_set_quantize(png_ptr, std_color_cube, jpayne@68: MAX_SCREEN_COLORS, MAX_SCREEN_COLORS, jpayne@68: NULL,0); jpayne@68: } jpayne@68: } jpayne@68: jpayne@68: PNG files describe monochrome as black being zero and white being one. jpayne@68: The following code will reverse this (make black be one and white be jpayne@68: zero): jpayne@68: jpayne@68: if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY) jpayne@68: png_set_invert_mono(png_ptr); jpayne@68: jpayne@68: This function can also be used to invert grayscale and gray-alpha images: jpayne@68: jpayne@68: if (color_type == PNG_COLOR_TYPE_GRAY || jpayne@68: color_type == PNG_COLOR_TYPE_GRAY_ALPHA) jpayne@68: png_set_invert_mono(png_ptr); jpayne@68: jpayne@68: PNG files store 16-bit pixels in network byte order (big-endian, jpayne@68: ie. most significant bits first). This code changes the storage to the jpayne@68: other way (little-endian, i.e. least significant bits first, the jpayne@68: way PCs store them): jpayne@68: jpayne@68: if (bit_depth == 16) jpayne@68: png_set_swap(png_ptr); jpayne@68: jpayne@68: If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you jpayne@68: need to change the order the pixels are packed into bytes, you can use: jpayne@68: jpayne@68: if (bit_depth < 8) jpayne@68: png_set_packswap(png_ptr); jpayne@68: jpayne@68: Finally, you can write your own transformation function if none of jpayne@68: the existing ones meets your needs. This is done by setting a callback jpayne@68: with jpayne@68: jpayne@68: png_set_read_user_transform_fn(png_ptr, jpayne@68: read_transform_fn); jpayne@68: jpayne@68: You must supply the function jpayne@68: jpayne@68: void read_transform_fn(png_structp png_ptr, png_row_infop jpayne@68: row_info, png_bytep data) jpayne@68: jpayne@68: See pngtest.c for a working example. Your function will be called jpayne@68: after all of the other transformations have been processed. Take care with jpayne@68: interlaced images if you do the interlace yourself - the width of the row is the jpayne@68: width in 'row_info', not the overall image width. jpayne@68: jpayne@68: If supported, libpng provides two information routines that you can use to find jpayne@68: where you are in processing the image: jpayne@68: jpayne@68: png_get_current_pass_number(png_structp png_ptr); jpayne@68: png_get_current_row_number(png_structp png_ptr); jpayne@68: jpayne@68: Don't try using these outside a transform callback - firstly they are only jpayne@68: supported if user transforms are supported, secondly they may well return jpayne@68: unexpected results unless the row is actually being processed at the moment they jpayne@68: are called. jpayne@68: jpayne@68: With interlaced jpayne@68: images the value returned is the row in the input sub-image image. Use jpayne@68: PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to jpayne@68: find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass). jpayne@68: jpayne@68: The discussion of interlace handling above contains more information on how to jpayne@68: use these values. jpayne@68: jpayne@68: You can also set up a pointer to a user structure for use by your jpayne@68: callback function, and you can inform libpng that your transform jpayne@68: function will change the number of channels or bit depth with the jpayne@68: function jpayne@68: jpayne@68: png_set_user_transform_info(png_ptr, user_ptr, jpayne@68: user_depth, user_channels); jpayne@68: jpayne@68: The user's application, not libpng, is responsible for allocating and jpayne@68: freeing any memory required for the user structure. jpayne@68: jpayne@68: You can retrieve the pointer via the function jpayne@68: png_get_user_transform_ptr(). For example: jpayne@68: jpayne@68: voidp read_user_transform_ptr = jpayne@68: png_get_user_transform_ptr(png_ptr); jpayne@68: jpayne@68: The last thing to handle is interlacing; this is covered in detail below, jpayne@68: but you must call the function here if you want libpng to handle expansion jpayne@68: of the interlaced image. jpayne@68: jpayne@68: number_of_passes = png_set_interlace_handling(png_ptr); jpayne@68: jpayne@68: After setting the transformations, libpng can update your png_info jpayne@68: structure to reflect any transformations you've requested with this jpayne@68: call. jpayne@68: jpayne@68: png_read_update_info(png_ptr, info_ptr); jpayne@68: jpayne@68: This is most useful to update the info structure's rowbytes jpayne@68: field so you can use it to allocate your image memory. This function jpayne@68: will also update your palette with the correct screen_gamma and jpayne@68: background if these have been given with the calls above. You may jpayne@68: only call png_read_update_info() once with a particular info_ptr. jpayne@68: jpayne@68: After you call png_read_update_info(), you can allocate any jpayne@68: memory you need to hold the image. The row data is simply jpayne@68: raw byte data for all forms of images. As the actual allocation jpayne@68: varies among applications, no example will be given. If you jpayne@68: are allocating one large chunk, you will need to build an jpayne@68: array of pointers to each row, as it will be needed for some jpayne@68: of the functions below. jpayne@68: jpayne@68: Be sure that your platform can allocate the buffer that you'll need. jpayne@68: libpng internally checks for oversize width, but you'll need to jpayne@68: do your own check for number_of_rows*width*pixel_size if you are using jpayne@68: a multiple-row buffer: jpayne@68: jpayne@68: /* Guard against integer overflow */ jpayne@68: if (number_of_rows > PNG_SIZE_MAX/(width*pixel_size)) jpayne@68: png_error(png_ptr, "image_data buffer would be too large"); jpayne@68: jpayne@68: Remember: Before you call png_read_update_info(), the png_get_*() jpayne@68: functions return the values corresponding to the original PNG image. jpayne@68: After you call png_read_update_info the values refer to the image jpayne@68: that libpng will output. Consequently you must call all the png_set_ jpayne@68: functions before you call png_read_update_info(). This is particularly jpayne@68: important for png_set_interlace_handling() - if you are going to call jpayne@68: png_read_update_info() you must call png_set_interlace_handling() before jpayne@68: it unless you want to receive interlaced output. jpayne@68: jpayne@68: .SS Reading image data jpayne@68: jpayne@68: After you've allocated memory, you can read the image data. jpayne@68: The simplest way to do this is in one function call. If you are jpayne@68: allocating enough memory to hold the whole image, you can just jpayne@68: call png_read_image() and libpng will read in all the image data jpayne@68: and put it in the memory area supplied. You will need to pass in jpayne@68: an array of pointers to each row. jpayne@68: jpayne@68: This function automatically handles interlacing, so you don't jpayne@68: need to call png_set_interlace_handling() (unless you call jpayne@68: png_read_update_info()) or call this function multiple times, or any jpayne@68: of that other stuff necessary with png_read_rows(). jpayne@68: jpayne@68: png_read_image(png_ptr, row_pointers); jpayne@68: jpayne@68: where row_pointers is: jpayne@68: jpayne@68: png_bytep row_pointers[height]; jpayne@68: jpayne@68: You can point to void or char or whatever you use for pixels. jpayne@68: jpayne@68: If you don't want to read in the whole image at once, you can jpayne@68: use png_read_rows() instead. If there is no interlacing (check jpayne@68: interlace_type == PNG_INTERLACE_NONE), this is simple: jpayne@68: jpayne@68: png_read_rows(png_ptr, row_pointers, NULL, jpayne@68: number_of_rows); jpayne@68: jpayne@68: where row_pointers is the same as in the png_read_image() call. jpayne@68: jpayne@68: If you are doing this just one row at a time, you can do this with jpayne@68: a single row_pointer instead of an array of row_pointers: jpayne@68: jpayne@68: png_bytep row_pointer = row; jpayne@68: png_read_row(png_ptr, row_pointer, NULL); jpayne@68: jpayne@68: If the file is interlaced (interlace_type != 0 in the IHDR chunk), things jpayne@68: get somewhat harder. The only current (PNG Specification version 1.2) jpayne@68: interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7); jpayne@68: a somewhat complicated 2D interlace scheme, known as Adam7, that jpayne@68: breaks down an image into seven smaller images of varying size, based jpayne@68: on an 8x8 grid. This number is defined (from libpng 1.5) as jpayne@68: PNG_INTERLACE_ADAM7_PASSES in png.h jpayne@68: jpayne@68: libpng can fill out those images or it can give them to you "as is". jpayne@68: It is almost always better to have libpng handle the interlacing for you. jpayne@68: If you want the images filled out, there are two ways to do that. The one jpayne@68: mentioned in the PNG specification is to expand each pixel to cover jpayne@68: those pixels that have not been read yet (the "rectangle" method). jpayne@68: This results in a blocky image for the first pass, which gradually jpayne@68: smooths out as more pixels are read. The other method is the "sparkle" jpayne@68: method, where pixels are drawn only in their final locations, with the jpayne@68: rest of the image remaining whatever colors they were initialized to jpayne@68: before the start of the read. The first method usually looks better, jpayne@68: but tends to be slower, as there are more pixels to put in the rows. jpayne@68: jpayne@68: If, as is likely, you want libpng to expand the images, call this before jpayne@68: calling png_start_read_image() or png_read_update_info(): jpayne@68: jpayne@68: if (interlace_type == PNG_INTERLACE_ADAM7) jpayne@68: number_of_passes jpayne@68: = png_set_interlace_handling(png_ptr); jpayne@68: jpayne@68: This will return the number of passes needed. Currently, this is seven, jpayne@68: but may change if another interlace type is added. This function can be jpayne@68: called even if the file is not interlaced, where it will return one pass. jpayne@68: You then need to read the whole image 'number_of_passes' times. Each time jpayne@68: will distribute the pixels from the current pass to the correct place in jpayne@68: the output image, so you need to supply the same rows to png_read_rows in jpayne@68: each pass. jpayne@68: jpayne@68: If you are not going to display the image after each pass, but are jpayne@68: going to wait until the entire image is read in, use the sparkle jpayne@68: effect. This effect is faster and the end result of either method jpayne@68: is exactly the same. If you are planning on displaying the image jpayne@68: after each pass, the "rectangle" effect is generally considered the jpayne@68: better looking one. jpayne@68: jpayne@68: If you only want the "sparkle" effect, just call png_read_row() or jpayne@68: png_read_rows() as jpayne@68: normal, with the third parameter NULL. Make sure you make pass over jpayne@68: the image number_of_passes times, and you don't change the data in the jpayne@68: rows between calls. You can change the locations of the data, just jpayne@68: not the data. Each pass only writes the pixels appropriate for that jpayne@68: pass, and assumes the data from previous passes is still valid. jpayne@68: jpayne@68: png_read_rows(png_ptr, row_pointers, NULL, jpayne@68: number_of_rows); jpayne@68: or jpayne@68: png_read_row(png_ptr, row_pointers, NULL); jpayne@68: jpayne@68: If you only want the first effect (the rectangles), do the same as jpayne@68: before except pass the row buffer in the third parameter, and leave jpayne@68: the second parameter NULL. jpayne@68: jpayne@68: png_read_rows(png_ptr, NULL, row_pointers, jpayne@68: number_of_rows); jpayne@68: or jpayne@68: png_read_row(png_ptr, NULL, row_pointers); jpayne@68: jpayne@68: If you don't want libpng to handle the interlacing details, just call jpayne@68: png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images. jpayne@68: Each of the images is a valid image by itself; however, you will almost jpayne@68: certainly need to distribute the pixels from each sub-image to the jpayne@68: correct place. This is where everything gets very tricky. jpayne@68: jpayne@68: If you want to retrieve the separate images you must pass the correct jpayne@68: number of rows to each successive call of png_read_rows(). The calculation jpayne@68: gets pretty complicated for small images, where some sub-images may jpayne@68: not even exist because either their width or height ends up zero. jpayne@68: libpng provides two macros to help you in 1.5 and later versions: jpayne@68: jpayne@68: png_uint_32 width = PNG_PASS_COLS(image_width, pass_number); jpayne@68: png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number); jpayne@68: jpayne@68: Respectively these tell you the width and height of the sub-image jpayne@68: corresponding to the numbered pass. 'pass' is in in the range 0 to 6 - jpayne@68: this can be confusing because the specification refers to the same passes jpayne@68: as 1 to 7! Be careful, you must check both the width and height before jpayne@68: calling png_read_rows() and not call it for that pass if either is zero. jpayne@68: jpayne@68: You can, of course, read each sub-image row by row. If you want to jpayne@68: produce optimal code to make a pixel-by-pixel transformation of an jpayne@68: interlaced image this is the best approach; read each row of each pass, jpayne@68: transform it, and write it out to a new interlaced image. jpayne@68: jpayne@68: If you want to de-interlace the image yourself libpng provides further jpayne@68: macros to help that tell you where to place the pixels in the output image. jpayne@68: Because the interlacing scheme is rectangular - sub-image pixels are always jpayne@68: arranged on a rectangular grid - all you need to know for each pass is the jpayne@68: starting column and row in the output image of the first pixel plus the jpayne@68: spacing between each pixel. As of libpng 1.5 there are four macros to jpayne@68: retrieve this information: jpayne@68: jpayne@68: png_uint_32 x = PNG_PASS_START_COL(pass); jpayne@68: png_uint_32 y = PNG_PASS_START_ROW(pass); jpayne@68: png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass); jpayne@68: png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass); jpayne@68: jpayne@68: These allow you to write the obvious loop: jpayne@68: jpayne@68: png_uint_32 input_y = 0; jpayne@68: png_uint_32 output_y = PNG_PASS_START_ROW(pass); jpayne@68: jpayne@68: while (output_y < output_image_height) jpayne@68: { jpayne@68: png_uint_32 input_x = 0; jpayne@68: png_uint_32 output_x = PNG_PASS_START_COL(pass); jpayne@68: jpayne@68: while (output_x < output_image_width) jpayne@68: { jpayne@68: image[output_y][output_x] = jpayne@68: subimage[pass][input_y][input_x++]; jpayne@68: jpayne@68: output_x += xStep; jpayne@68: } jpayne@68: jpayne@68: ++input_y; jpayne@68: output_y += yStep; jpayne@68: } jpayne@68: jpayne@68: Notice that the steps between successive output rows and columns are jpayne@68: returned as shifts. This is possible because the pixels in the subimages jpayne@68: are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original jpayne@68: image. In practice you may need to directly calculate the output coordinate jpayne@68: given an input coordinate. libpng provides two further macros for this jpayne@68: purpose: jpayne@68: jpayne@68: png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass); jpayne@68: png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass); jpayne@68: jpayne@68: Finally a pair of macros are provided to tell you if a particular image jpayne@68: row or column appears in a given pass: jpayne@68: jpayne@68: int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass); jpayne@68: int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass); jpayne@68: jpayne@68: Bear in mind that you will probably also need to check the width and height jpayne@68: of the pass in addition to the above to be sure the pass even exists! jpayne@68: jpayne@68: With any luck you are convinced by now that you don't want to do your own jpayne@68: interlace handling. In reality normally the only good reason for doing this jpayne@68: is if you are processing PNG files on a pixel-by-pixel basis and don't want jpayne@68: to load the whole file into memory when it is interlaced. jpayne@68: jpayne@68: libpng includes a test program, pngvalid, that illustrates reading and jpayne@68: writing of interlaced images. If you can't get interlacing to work in your jpayne@68: code and don't want to leave it to libpng (the recommended approach), see jpayne@68: how pngvalid.c does it. jpayne@68: jpayne@68: .SS Finishing a sequential read jpayne@68: jpayne@68: After you are finished reading the image through the jpayne@68: low-level interface, you can finish reading the file. jpayne@68: jpayne@68: If you want to use a different crc action for handling CRC errors in jpayne@68: chunks after the image data, you can call png_set_crc_action() jpayne@68: again at this point. jpayne@68: jpayne@68: If you are interested in comments or time, which may be stored either jpayne@68: before or after the image data, you should pass the separate png_info jpayne@68: struct if you want to keep the comments from before and after the image jpayne@68: separate. jpayne@68: jpayne@68: png_infop end_info = png_create_info_struct(png_ptr); jpayne@68: jpayne@68: if (!end_info) jpayne@68: { jpayne@68: png_destroy_read_struct(&png_ptr, &info_ptr, NULL); jpayne@68: return ERROR; jpayne@68: } jpayne@68: jpayne@68: png_read_end(png_ptr, end_info); jpayne@68: jpayne@68: If you are not interested, you should still call png_read_end() jpayne@68: but you can pass NULL, avoiding the need to create an end_info structure. jpayne@68: If you do this, libpng will not process any chunks after IDAT other than jpayne@68: skipping over them and perhaps (depending on whether you have called jpayne@68: png_set_crc_action) checking their CRCs while looking for the IEND chunk. jpayne@68: jpayne@68: png_read_end(png_ptr, NULL); jpayne@68: jpayne@68: If you don't call png_read_end(), then your file pointer will be jpayne@68: left pointing to the first chunk after the last IDAT, which is probably jpayne@68: not what you want if you expect to read something beyond the end of jpayne@68: the PNG datastream. jpayne@68: jpayne@68: When you are done, you can free all memory allocated by libpng like this: jpayne@68: jpayne@68: png_destroy_read_struct(&png_ptr, &info_ptr, &end_info); jpayne@68: jpayne@68: or, if you didn't create an end_info structure, jpayne@68: jpayne@68: png_destroy_read_struct(&png_ptr, &info_ptr, NULL); jpayne@68: jpayne@68: It is also possible to individually free the info_ptr members that jpayne@68: point to libpng-allocated storage with the following function: jpayne@68: jpayne@68: png_free_data(png_ptr, info_ptr, mask, seq) jpayne@68: jpayne@68: mask - identifies data to be freed, a mask jpayne@68: containing the bitwise OR of one or jpayne@68: more of jpayne@68: PNG_FREE_PLTE, PNG_FREE_TRNS, jpayne@68: PNG_FREE_HIST, PNG_FREE_ICCP, jpayne@68: PNG_FREE_PCAL, PNG_FREE_ROWS, jpayne@68: PNG_FREE_SCAL, PNG_FREE_SPLT, jpayne@68: PNG_FREE_TEXT, PNG_FREE_UNKN, jpayne@68: or simply PNG_FREE_ALL jpayne@68: jpayne@68: seq - sequence number of item to be freed jpayne@68: (\-1 for all items) jpayne@68: jpayne@68: This function may be safely called when the relevant storage has jpayne@68: already been freed, or has not yet been allocated, or was allocated jpayne@68: by the user and not by libpng, and will in those cases do nothing. jpayne@68: The "seq" parameter is ignored if only one item of the selected data jpayne@68: type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items jpayne@68: are allowed for the data type identified in the mask, such as text or jpayne@68: sPLT, only the n'th item in the structure is freed, where n is "seq". jpayne@68: jpayne@68: The default behavior is only to free data that was allocated internally jpayne@68: by libpng. This can be changed, so that libpng will not free the data, jpayne@68: or so that it will free data that was allocated by the user with png_malloc() jpayne@68: or png_calloc() and passed in via a png_set_*() function, with jpayne@68: jpayne@68: png_data_freer(png_ptr, info_ptr, freer, mask) jpayne@68: jpayne@68: freer - one of jpayne@68: PNG_DESTROY_WILL_FREE_DATA jpayne@68: PNG_SET_WILL_FREE_DATA jpayne@68: PNG_USER_WILL_FREE_DATA jpayne@68: jpayne@68: mask - which data elements are affected jpayne@68: same choices as in png_free_data() jpayne@68: jpayne@68: This function only affects data that has already been allocated. jpayne@68: You can call this function after reading the PNG data but before calling jpayne@68: any png_set_*() functions, to control whether the user or the png_set_*() jpayne@68: function is responsible for freeing any existing data that might be present, jpayne@68: and again after the png_set_*() functions to control whether the user jpayne@68: or png_destroy_*() is supposed to free the data. When the user assumes jpayne@68: responsibility for libpng-allocated data, the application must use jpayne@68: png_free() to free it, and when the user transfers responsibility to libpng jpayne@68: for data that the user has allocated, the user must have used png_malloc() jpayne@68: or png_calloc() to allocate it. jpayne@68: jpayne@68: If you allocated your row_pointers in a single block, as suggested above in jpayne@68: the description of the high level read interface, you must not transfer jpayne@68: responsibility for freeing it to the png_set_rows or png_read_destroy function, jpayne@68: because they would also try to free the individual row_pointers[i]. jpayne@68: jpayne@68: If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword jpayne@68: separately, do not transfer responsibility for freeing text_ptr to libpng, jpayne@68: because when libpng fills a png_text structure it combines these members with jpayne@68: the key member, and png_free_data() will free only text_ptr.key. Similarly, jpayne@68: if you transfer responsibility for free'ing text_ptr from libpng to your jpayne@68: application, your application must not separately free those members. jpayne@68: jpayne@68: The png_free_data() function will turn off the "valid" flag for anything jpayne@68: it frees. If you need to turn the flag off for a chunk that was freed by jpayne@68: your application instead of by libpng, you can use jpayne@68: jpayne@68: png_set_invalid(png_ptr, info_ptr, mask); jpayne@68: jpayne@68: mask - identifies the chunks to be made invalid, jpayne@68: containing the bitwise OR of one or jpayne@68: more of jpayne@68: PNG_INFO_gAMA, PNG_INFO_sBIT, jpayne@68: PNG_INFO_cHRM, PNG_INFO_PLTE, jpayne@68: PNG_INFO_tRNS, PNG_INFO_bKGD, jpayne@68: PNG_INFO_eXIf, jpayne@68: PNG_INFO_hIST, PNG_INFO_pHYs, jpayne@68: PNG_INFO_oFFs, PNG_INFO_tIME, jpayne@68: PNG_INFO_pCAL, PNG_INFO_sRGB, jpayne@68: PNG_INFO_iCCP, PNG_INFO_sPLT, jpayne@68: PNG_INFO_sCAL, PNG_INFO_IDAT jpayne@68: jpayne@68: For a more compact example of reading a PNG image, see the file example.c. jpayne@68: jpayne@68: .SS Reading PNG files progressively jpayne@68: jpayne@68: The progressive reader is slightly different from the non-progressive jpayne@68: reader. Instead of calling png_read_info(), png_read_rows(), and jpayne@68: png_read_end(), you make one call to png_process_data(), which calls jpayne@68: callbacks when it has the info, a row, or the end of the image. You jpayne@68: set up these callbacks with png_set_progressive_read_fn(). You don't jpayne@68: have to worry about the input/output functions of libpng, as you are jpayne@68: giving the library the data directly in png_process_data(). I will jpayne@68: assume that you have read the section on reading PNG files above, jpayne@68: so I will only highlight the differences (although I will show jpayne@68: all of the code). jpayne@68: jpayne@68: png_structp png_ptr; jpayne@68: png_infop info_ptr; jpayne@68: jpayne@68: /* An example code fragment of how you would jpayne@68: initialize the progressive reader in your jpayne@68: application. */ jpayne@68: int jpayne@68: initialize_png_reader() jpayne@68: { jpayne@68: png_ptr = png_create_read_struct jpayne@68: (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, jpayne@68: user_error_fn, user_warning_fn); jpayne@68: jpayne@68: if (!png_ptr) jpayne@68: return ERROR; jpayne@68: jpayne@68: info_ptr = png_create_info_struct(png_ptr); jpayne@68: jpayne@68: if (!info_ptr) jpayne@68: { jpayne@68: png_destroy_read_struct(&png_ptr, NULL, NULL); jpayne@68: return ERROR; jpayne@68: } jpayne@68: jpayne@68: if (setjmp(png_jmpbuf(png_ptr))) jpayne@68: { jpayne@68: png_destroy_read_struct(&png_ptr, &info_ptr, NULL); jpayne@68: return ERROR; jpayne@68: } jpayne@68: jpayne@68: /* This one's new. You can provide functions jpayne@68: to be called when the header info is valid, jpayne@68: when each row is completed, and when the image jpayne@68: is finished. If you aren't using all functions, jpayne@68: you can specify NULL parameters. Even when all jpayne@68: three functions are NULL, you need to call jpayne@68: png_set_progressive_read_fn(). You can use jpayne@68: any struct as the user_ptr (cast to a void pointer jpayne@68: for the function call), and retrieve the pointer jpayne@68: from inside the callbacks using the function jpayne@68: jpayne@68: png_get_progressive_ptr(png_ptr); jpayne@68: jpayne@68: which will return a void pointer, which you have jpayne@68: to cast appropriately. jpayne@68: */ jpayne@68: png_set_progressive_read_fn(png_ptr, (void *)user_ptr, jpayne@68: info_callback, row_callback, end_callback); jpayne@68: jpayne@68: return 0; jpayne@68: } jpayne@68: jpayne@68: /* A code fragment that you call as you receive blocks jpayne@68: of data */ jpayne@68: int jpayne@68: process_data(png_bytep buffer, png_uint_32 length) jpayne@68: { jpayne@68: if (setjmp(png_jmpbuf(png_ptr))) jpayne@68: { jpayne@68: png_destroy_read_struct(&png_ptr, &info_ptr, NULL); jpayne@68: return ERROR; jpayne@68: } jpayne@68: jpayne@68: /* This one's new also. Simply give it a chunk jpayne@68: of data from the file stream (in order, of jpayne@68: course). On machines with segmented memory jpayne@68: models machines, don't give it any more than jpayne@68: 64K. The library seems to run fine with sizes jpayne@68: of 4K. Although you can give it much less if jpayne@68: necessary (I assume you can give it chunks of jpayne@68: 1 byte, I haven't tried less than 256 bytes jpayne@68: yet). When this function returns, you may jpayne@68: want to display any rows that were generated jpayne@68: in the row callback if you don't already do jpayne@68: so there. jpayne@68: */ jpayne@68: png_process_data(png_ptr, info_ptr, buffer, length); jpayne@68: jpayne@68: /* At this point you can call png_process_data_skip if jpayne@68: you want to handle data the library will skip yourself; jpayne@68: it simply returns the number of bytes to skip (and stops jpayne@68: libpng skipping that number of bytes on the next jpayne@68: png_process_data call). jpayne@68: return 0; jpayne@68: } jpayne@68: jpayne@68: /* This function is called (as set by jpayne@68: png_set_progressive_read_fn() above) when enough data jpayne@68: has been supplied so all of the header has been jpayne@68: read. jpayne@68: */ jpayne@68: void jpayne@68: info_callback(png_structp png_ptr, png_infop info) jpayne@68: { jpayne@68: /* Do any setup here, including setting any of jpayne@68: the transformations mentioned in the Reading jpayne@68: PNG files section. For now, you _must_ call jpayne@68: either png_start_read_image() or jpayne@68: png_read_update_info() after all the jpayne@68: transformations are set (even if you don't set jpayne@68: any). You may start getting rows before jpayne@68: png_process_data() returns, so this is your jpayne@68: last chance to prepare for that. jpayne@68: jpayne@68: This is where you turn on interlace handling, jpayne@68: assuming you don't want to do it yourself. jpayne@68: jpayne@68: If you need to you can stop the processing of jpayne@68: your original input data at this point by calling jpayne@68: png_process_data_pause. This returns the number jpayne@68: of unprocessed bytes from the last png_process_data jpayne@68: call - it is up to you to ensure that the next call jpayne@68: sees these bytes again. If you don't want to bother jpayne@68: with this you can get libpng to cache the unread jpayne@68: bytes by setting the 'save' parameter (see png.h) but jpayne@68: then libpng will have to copy the data internally. jpayne@68: */ jpayne@68: } jpayne@68: jpayne@68: /* This function is called when each row of image jpayne@68: data is complete */ jpayne@68: void jpayne@68: row_callback(png_structp png_ptr, png_bytep new_row, jpayne@68: png_uint_32 row_num, int pass) jpayne@68: { jpayne@68: /* If the image is interlaced, and you turned jpayne@68: on the interlace handler, this function will jpayne@68: be called for every row in every pass. Some jpayne@68: of these rows will not be changed from the jpayne@68: previous pass. When the row is not changed, jpayne@68: the new_row variable will be NULL. The rows jpayne@68: and passes are called in order, so you don't jpayne@68: really need the row_num and pass, but I'm jpayne@68: supplying them because it may make your life jpayne@68: easier. jpayne@68: jpayne@68: If you did not turn on interlace handling then jpayne@68: the callback is called for each row of each jpayne@68: sub-image when the image is interlaced. In this jpayne@68: case 'row_num' is the row in the sub-image, not jpayne@68: the row in the output image as it is in all other jpayne@68: cases. jpayne@68: jpayne@68: For the non-NULL rows of interlaced images when jpayne@68: you have switched on libpng interlace handling, jpayne@68: you must call png_progressive_combine_row() jpayne@68: passing in the row and the old row. You can jpayne@68: call this function for NULL rows (it will just jpayne@68: return) and for non-interlaced images (it just jpayne@68: does the memcpy for you) if it will make the jpayne@68: code easier. Thus, you can just do this for jpayne@68: all cases if you switch on interlace handling; jpayne@68: */ jpayne@68: jpayne@68: png_progressive_combine_row(png_ptr, old_row, jpayne@68: new_row); jpayne@68: jpayne@68: /* where old_row is what was displayed jpayne@68: previously for the row. Note that the first jpayne@68: pass (pass == 0, really) will completely cover jpayne@68: the old row, so the rows do not have to be jpayne@68: initialized. After the first pass (and only jpayne@68: for interlaced images), you will have to pass jpayne@68: the current row, and the function will combine jpayne@68: the old row and the new row. jpayne@68: jpayne@68: You can also call png_process_data_pause in this jpayne@68: callback - see above. jpayne@68: */ jpayne@68: } jpayne@68: jpayne@68: void jpayne@68: end_callback(png_structp png_ptr, png_infop info) jpayne@68: { jpayne@68: /* This function is called after the whole image jpayne@68: has been read, including any chunks after the jpayne@68: image (up to and including the IEND). You jpayne@68: will usually have the same info chunk as you jpayne@68: had in the header, although some data may have jpayne@68: been added to the comments and time fields. jpayne@68: jpayne@68: Most people won't do much here, perhaps setting jpayne@68: a flag that marks the image as finished. jpayne@68: */ jpayne@68: } jpayne@68: jpayne@68: jpayne@68: jpayne@68: .SH IV. Writing jpayne@68: jpayne@68: Much of this is very similar to reading. However, everything of jpayne@68: importance is repeated here, so you won't have to constantly look jpayne@68: back up in the reading section to understand writing. jpayne@68: jpayne@68: .SS Setup jpayne@68: jpayne@68: You will want to do the I/O initialization before you get into libpng, jpayne@68: so if it doesn't work, you don't have anything to undo. If you are not jpayne@68: using the standard I/O functions, you will need to replace them with jpayne@68: custom writing functions. See the discussion under Customizing libpng. jpayne@68: jpayne@68: FILE *fp = fopen(file_name, "wb"); jpayne@68: jpayne@68: if (!fp) jpayne@68: return ERROR; jpayne@68: jpayne@68: Next, png_struct and png_info need to be allocated and initialized. jpayne@68: As these can be both relatively large, you may not want to store these jpayne@68: on the stack, unless you have stack space to spare. Of course, you jpayne@68: will want to check if they return NULL. If you are also reading, jpayne@68: you won't want to name your read structure and your write structure jpayne@68: both "png_ptr"; you can call them anything you like, such as jpayne@68: "read_ptr" and "write_ptr". Look at pngtest.c, for example. jpayne@68: jpayne@68: png_structp png_ptr = png_create_write_struct jpayne@68: (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, jpayne@68: user_error_fn, user_warning_fn); jpayne@68: jpayne@68: if (!png_ptr) jpayne@68: return ERROR; jpayne@68: jpayne@68: png_infop info_ptr = png_create_info_struct(png_ptr); jpayne@68: if (!info_ptr) jpayne@68: { jpayne@68: png_destroy_write_struct(&png_ptr, NULL); jpayne@68: return ERROR; jpayne@68: } jpayne@68: jpayne@68: If you want to use your own memory allocation routines, jpayne@68: define PNG_USER_MEM_SUPPORTED and use jpayne@68: png_create_write_struct_2() instead of png_create_write_struct(): jpayne@68: jpayne@68: png_structp png_ptr = png_create_write_struct_2 jpayne@68: (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, jpayne@68: user_error_fn, user_warning_fn, (png_voidp) jpayne@68: user_mem_ptr, user_malloc_fn, user_free_fn); jpayne@68: jpayne@68: After you have these structures, you will need to set up the jpayne@68: error handling. When libpng encounters an error, it expects to jpayne@68: longjmp() back to your routine. Therefore, you will need to call jpayne@68: setjmp() and pass the png_jmpbuf(png_ptr). If you jpayne@68: write the file from different routines, you will need to update jpayne@68: the png_jmpbuf(png_ptr) every time you enter a new routine that will jpayne@68: call a png_*() function. See your documentation of setjmp/longjmp jpayne@68: for your compiler for more information on setjmp/longjmp. See jpayne@68: the discussion on libpng error handling in the Customizing Libpng jpayne@68: section below for more information on the libpng error handling. jpayne@68: jpayne@68: if (setjmp(png_jmpbuf(png_ptr))) jpayne@68: { jpayne@68: png_destroy_write_struct(&png_ptr, &info_ptr); jpayne@68: fclose(fp); jpayne@68: return ERROR; jpayne@68: } jpayne@68: ... jpayne@68: return; jpayne@68: jpayne@68: If you would rather avoid the complexity of setjmp/longjmp issues, jpayne@68: you can compile libpng with PNG_NO_SETJMP, in which case jpayne@68: errors will result in a call to PNG_ABORT() which defaults to abort(). jpayne@68: jpayne@68: You can #define PNG_ABORT() to a function that does something jpayne@68: more useful than abort(), as long as your function does not jpayne@68: return. jpayne@68: jpayne@68: Checking for invalid palette index on write was added at libpng jpayne@68: 1.5.10. If a pixel contains an invalid (out-of-range) index libpng issues jpayne@68: a benign error. This is enabled by default because this condition is an jpayne@68: error according to the PNG specification, Clause 11.3.2, but the error can jpayne@68: be ignored in each png_ptr with jpayne@68: jpayne@68: png_set_check_for_invalid_index(png_ptr, 0); jpayne@68: jpayne@68: If the error is ignored, or if png_benign_error() treats it as a warning, jpayne@68: any invalid pixels are written as-is by the encoder, resulting in an jpayne@68: invalid PNG datastream as output. In this case the application is jpayne@68: responsible for ensuring that the pixel indexes are in range when it writes jpayne@68: a PLTE chunk with fewer entries than the bit depth would allow. jpayne@68: jpayne@68: Now you need to set up the output code. The default for libpng is to jpayne@68: use the C function fwrite(). If you use this, you will need to pass a jpayne@68: valid FILE * in the function png_init_io(). Be sure that the file is jpayne@68: opened in binary mode. Again, if you wish to handle writing data in jpayne@68: another way, see the discussion on libpng I/O handling in the Customizing jpayne@68: Libpng section below. jpayne@68: jpayne@68: png_init_io(png_ptr, fp); jpayne@68: jpayne@68: If you are embedding your PNG into a datastream such as MNG, and don't jpayne@68: want libpng to write the 8-byte signature, or if you have already jpayne@68: written the signature in your application, use jpayne@68: jpayne@68: png_set_sig_bytes(png_ptr, 8); jpayne@68: jpayne@68: to inform libpng that it should not write a signature. jpayne@68: jpayne@68: .SS Write callbacks jpayne@68: jpayne@68: At this point, you can set up a callback function that will be jpayne@68: called after each row has been written, which you can use to control jpayne@68: a progress meter or the like. It's demonstrated in pngtest.c. jpayne@68: You must supply a function jpayne@68: jpayne@68: void write_row_callback(png_structp png_ptr, png_uint_32 row, jpayne@68: int pass) jpayne@68: { jpayne@68: /* put your code here */ jpayne@68: } jpayne@68: jpayne@68: (You can give it another name that you like instead of "write_row_callback") jpayne@68: jpayne@68: To inform libpng about your function, use jpayne@68: jpayne@68: png_set_write_status_fn(png_ptr, write_row_callback); jpayne@68: jpayne@68: When this function is called the row has already been completely processed and jpayne@68: it has also been written out. The 'row' and 'pass' refer to the next row to be jpayne@68: handled. For the jpayne@68: non-interlaced case the row that was just handled is simply one less than the jpayne@68: passed in row number, and pass will always be 0. For the interlaced case the jpayne@68: same applies unless the row value is 0, in which case the row just handled was jpayne@68: the last one from one of the preceding passes. Because interlacing may skip a jpayne@68: pass you cannot be sure that the preceding pass is just 'pass\-1', if you really jpayne@68: need to know what the last pass is record (row,pass) from the callback and use jpayne@68: the last recorded value each time. jpayne@68: jpayne@68: As with the user transform you can find the output row using the jpayne@68: PNG_ROW_FROM_PASS_ROW macro. jpayne@68: jpayne@68: You now have the option of modifying how the compression library will jpayne@68: run. The following functions are mainly for testing, but may be useful jpayne@68: in some cases, like if you need to write PNG files extremely fast and jpayne@68: are willing to give up some compression, or if you want to get the jpayne@68: maximum possible compression at the expense of slower writing. If you jpayne@68: have no special needs in this area, let the library do what it wants by jpayne@68: not calling this function at all, as it has been tuned to deliver a good jpayne@68: speed/compression ratio. The second parameter to png_set_filter() is jpayne@68: the filter method, for which the only valid values are 0 (as of the jpayne@68: July 1999 PNG specification, version 1.2) or 64 (if you are writing jpayne@68: a PNG datastream that is to be embedded in a MNG datastream). The third jpayne@68: parameter is a flag that indicates which filter type(s) are to be tested jpayne@68: for each scanline. See the PNG specification for details on the specific jpayne@68: filter types. jpayne@68: jpayne@68: jpayne@68: /* turn on or off filtering, and/or choose jpayne@68: specific filters. You can use either a single jpayne@68: PNG_FILTER_VALUE_NAME or the bitwise OR of one jpayne@68: or more PNG_FILTER_NAME masks. jpayne@68: */ jpayne@68: png_set_filter(png_ptr, 0, jpayne@68: PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE | jpayne@68: PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB | jpayne@68: PNG_FILTER_UP | PNG_FILTER_VALUE_UP | jpayne@68: PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG | jpayne@68: PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH| jpayne@68: PNG_ALL_FILTERS | PNG_FAST_FILTERS); jpayne@68: jpayne@68: If an application wants to start and stop using particular filters during jpayne@68: compression, it should start out with all of the filters (to ensure that jpayne@68: the previous row of pixels will be stored in case it's needed later), jpayne@68: and then add and remove them after the start of compression. jpayne@68: jpayne@68: If you are writing a PNG datastream that is to be embedded in a MNG jpayne@68: datastream, the second parameter can be either 0 or 64. jpayne@68: jpayne@68: The png_set_compression_*() functions interface to the zlib compression jpayne@68: library, and should mostly be ignored unless you really know what you are jpayne@68: doing. The only generally useful call is png_set_compression_level() jpayne@68: which changes how much time zlib spends on trying to compress the image jpayne@68: data. See the Compression Library (zlib.h and algorithm.txt, distributed jpayne@68: with zlib) for details on the compression levels. jpayne@68: jpayne@68: #include zlib.h jpayne@68: jpayne@68: /* Set the zlib compression level */ jpayne@68: png_set_compression_level(png_ptr, jpayne@68: Z_BEST_COMPRESSION); jpayne@68: jpayne@68: /* Set other zlib parameters for compressing IDAT */ jpayne@68: png_set_compression_mem_level(png_ptr, 8); jpayne@68: png_set_compression_strategy(png_ptr, jpayne@68: Z_DEFAULT_STRATEGY); jpayne@68: png_set_compression_window_bits(png_ptr, 15); jpayne@68: png_set_compression_method(png_ptr, 8); jpayne@68: png_set_compression_buffer_size(png_ptr, 8192) jpayne@68: jpayne@68: /* Set zlib parameters for text compression jpayne@68: * If you don't call these, the parameters jpayne@68: * fall back on those defined for IDAT chunks jpayne@68: */ jpayne@68: png_set_text_compression_mem_level(png_ptr, 8); jpayne@68: png_set_text_compression_strategy(png_ptr, jpayne@68: Z_DEFAULT_STRATEGY); jpayne@68: png_set_text_compression_window_bits(png_ptr, 15); jpayne@68: png_set_text_compression_method(png_ptr, 8); jpayne@68: jpayne@68: .SS Setting the contents of info for output jpayne@68: jpayne@68: You now need to fill in the png_info structure with all the data you jpayne@68: wish to write before the actual image. Note that the only thing you jpayne@68: are allowed to write after the image is the text chunks and the time jpayne@68: chunk (as of PNG Specification 1.2, anyway). See png_write_end() and jpayne@68: the latest PNG specification for more information on that. If you jpayne@68: wish to write them before the image, fill them in now, and flag that jpayne@68: data as being valid. If you want to wait until after the data, don't jpayne@68: fill them until png_write_end(). For all the fields in png_info and jpayne@68: their data types, see png.h. For explanations of what the fields jpayne@68: contain, see the PNG specification. jpayne@68: jpayne@68: Some of the more important parts of the png_info are: jpayne@68: jpayne@68: png_set_IHDR(png_ptr, info_ptr, width, height, jpayne@68: bit_depth, color_type, interlace_type, jpayne@68: compression_type, filter_method) jpayne@68: jpayne@68: width - holds the width of the image jpayne@68: in pixels (up to 2^31). jpayne@68: jpayne@68: height - holds the height of the image jpayne@68: in pixels (up to 2^31). jpayne@68: jpayne@68: bit_depth - holds the bit depth of one of the jpayne@68: image channels. jpayne@68: (valid values are 1, 2, 4, 8, 16 jpayne@68: and depend also on the jpayne@68: color_type. See also significant jpayne@68: bits (sBIT) below). jpayne@68: jpayne@68: color_type - describes which color/alpha jpayne@68: channels are present. jpayne@68: PNG_COLOR_TYPE_GRAY jpayne@68: (bit depths 1, 2, 4, 8, 16) jpayne@68: PNG_COLOR_TYPE_GRAY_ALPHA jpayne@68: (bit depths 8, 16) jpayne@68: PNG_COLOR_TYPE_PALETTE jpayne@68: (bit depths 1, 2, 4, 8) jpayne@68: PNG_COLOR_TYPE_RGB jpayne@68: (bit_depths 8, 16) jpayne@68: PNG_COLOR_TYPE_RGB_ALPHA jpayne@68: (bit_depths 8, 16) jpayne@68: jpayne@68: PNG_COLOR_MASK_PALETTE jpayne@68: PNG_COLOR_MASK_COLOR jpayne@68: PNG_COLOR_MASK_ALPHA jpayne@68: jpayne@68: interlace_type - PNG_INTERLACE_NONE or jpayne@68: PNG_INTERLACE_ADAM7 jpayne@68: jpayne@68: compression_type - (must be jpayne@68: PNG_COMPRESSION_TYPE_DEFAULT) jpayne@68: jpayne@68: filter_method - (must be PNG_FILTER_TYPE_DEFAULT jpayne@68: or, if you are writing a PNG to jpayne@68: be embedded in a MNG datastream, jpayne@68: can also be jpayne@68: PNG_INTRAPIXEL_DIFFERENCING) jpayne@68: jpayne@68: If you call png_set_IHDR(), the call must appear before any of the jpayne@68: other png_set_*() functions, because they might require access to some of jpayne@68: the IHDR settings. The remaining png_set_*() functions can be called jpayne@68: in any order. jpayne@68: jpayne@68: If you wish, you can reset the compression_type, interlace_type, or jpayne@68: filter_method later by calling png_set_IHDR() again; if you do this, the jpayne@68: width, height, bit_depth, and color_type must be the same in each call. jpayne@68: jpayne@68: png_set_PLTE(png_ptr, info_ptr, palette, jpayne@68: num_palette); jpayne@68: jpayne@68: palette - the palette for the file jpayne@68: (array of png_color) jpayne@68: num_palette - number of entries in the palette jpayne@68: jpayne@68: jpayne@68: png_set_gAMA(png_ptr, info_ptr, file_gamma); jpayne@68: png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma); jpayne@68: jpayne@68: file_gamma - the gamma at which the image was jpayne@68: created (PNG_INFO_gAMA) jpayne@68: jpayne@68: int_file_gamma - 100,000 times the gamma at which jpayne@68: the image was created jpayne@68: jpayne@68: png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y, jpayne@68: green_x, green_y, blue_x, blue_y) jpayne@68: png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X, jpayne@68: green_Y, green_Z, blue_X, blue_Y, blue_Z) jpayne@68: png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y, jpayne@68: int_red_x, int_red_y, int_green_x, int_green_y, jpayne@68: int_blue_x, int_blue_y) jpayne@68: png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y, jpayne@68: int_red_Z, int_green_X, int_green_Y, int_green_Z, jpayne@68: int_blue_X, int_blue_Y, int_blue_Z) jpayne@68: jpayne@68: {white,red,green,blue}_{x,y} jpayne@68: A color space encoding specified using the chromaticities jpayne@68: of the end points and the white point. jpayne@68: jpayne@68: {red,green,blue}_{X,Y,Z} jpayne@68: A color space encoding specified using the encoding end jpayne@68: points - the CIE tristimulus specification of the intended jpayne@68: color of the red, green and blue channels in the PNG RGB jpayne@68: data. The white point is simply the sum of the three end jpayne@68: points. jpayne@68: jpayne@68: png_set_sRGB(png_ptr, info_ptr, srgb_intent); jpayne@68: jpayne@68: srgb_intent - the rendering intent jpayne@68: (PNG_INFO_sRGB) The presence of jpayne@68: the sRGB chunk means that the pixel jpayne@68: data is in the sRGB color space. jpayne@68: This chunk also implies specific jpayne@68: values of gAMA and cHRM. Rendering jpayne@68: intent is the CSS-1 property that jpayne@68: has been defined by the International jpayne@68: Color Consortium jpayne@68: (http://www.color.org). jpayne@68: It can be one of jpayne@68: PNG_sRGB_INTENT_SATURATION, jpayne@68: PNG_sRGB_INTENT_PERCEPTUAL, jpayne@68: PNG_sRGB_INTENT_ABSOLUTE, or jpayne@68: PNG_sRGB_INTENT_RELATIVE. jpayne@68: jpayne@68: jpayne@68: png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr, jpayne@68: srgb_intent); jpayne@68: jpayne@68: srgb_intent - the rendering intent jpayne@68: (PNG_INFO_sRGB) The presence of the jpayne@68: sRGB chunk means that the pixel jpayne@68: data is in the sRGB color space. jpayne@68: This function also causes gAMA and jpayne@68: cHRM chunks with the specific values jpayne@68: that are consistent with sRGB to be jpayne@68: written. jpayne@68: jpayne@68: png_set_iCCP(png_ptr, info_ptr, name, compression_type, jpayne@68: profile, proflen); jpayne@68: jpayne@68: name - The profile name. jpayne@68: jpayne@68: compression_type - The compression type; always jpayne@68: PNG_COMPRESSION_TYPE_BASE for PNG 1.0. jpayne@68: You may give NULL to this argument to jpayne@68: ignore it. jpayne@68: jpayne@68: profile - International Color Consortium color jpayne@68: profile data. May contain NULs. jpayne@68: jpayne@68: proflen - length of profile data in bytes. jpayne@68: jpayne@68: png_set_sBIT(png_ptr, info_ptr, sig_bit); jpayne@68: jpayne@68: sig_bit - the number of significant bits for jpayne@68: (PNG_INFO_sBIT) each of the gray, red, jpayne@68: green, and blue channels, whichever are jpayne@68: appropriate for the given color type jpayne@68: (png_color_16) jpayne@68: jpayne@68: png_set_tRNS(png_ptr, info_ptr, trans_alpha, jpayne@68: num_trans, trans_color); jpayne@68: jpayne@68: trans_alpha - array of alpha (transparency) jpayne@68: entries for palette (PNG_INFO_tRNS) jpayne@68: jpayne@68: num_trans - number of transparent entries jpayne@68: (PNG_INFO_tRNS) jpayne@68: jpayne@68: trans_color - graylevel or color sample values jpayne@68: (in order red, green, blue) of the jpayne@68: single transparent color for jpayne@68: non-paletted images (PNG_INFO_tRNS) jpayne@68: jpayne@68: png_set_eXIf_1(png_ptr, info_ptr, num_exif, exif); jpayne@68: jpayne@68: exif - Exif profile (array of png_byte) jpayne@68: (PNG_INFO_eXIf) jpayne@68: jpayne@68: png_set_hIST(png_ptr, info_ptr, hist); jpayne@68: jpayne@68: hist - histogram of palette (array of jpayne@68: png_uint_16) (PNG_INFO_hIST) jpayne@68: jpayne@68: png_set_tIME(png_ptr, info_ptr, mod_time); jpayne@68: jpayne@68: mod_time - time image was last modified jpayne@68: (PNG_INFO_tIME) jpayne@68: jpayne@68: png_set_bKGD(png_ptr, info_ptr, background); jpayne@68: jpayne@68: background - background color (of type jpayne@68: png_color_16p) (PNG_INFO_bKGD) jpayne@68: jpayne@68: png_set_text(png_ptr, info_ptr, text_ptr, num_text); jpayne@68: jpayne@68: text_ptr - array of png_text holding image jpayne@68: comments jpayne@68: jpayne@68: text_ptr[i].compression - type of compression used jpayne@68: on "text" PNG_TEXT_COMPRESSION_NONE jpayne@68: PNG_TEXT_COMPRESSION_zTXt jpayne@68: PNG_ITXT_COMPRESSION_NONE jpayne@68: PNG_ITXT_COMPRESSION_zTXt jpayne@68: text_ptr[i].key - keyword for comment. Must contain jpayne@68: 1-79 characters. jpayne@68: text_ptr[i].text - text comments for current jpayne@68: keyword. Can be NULL or empty. jpayne@68: text_ptr[i].text_length - length of text string, jpayne@68: after decompression, 0 for iTXt jpayne@68: text_ptr[i].itxt_length - length of itxt string, jpayne@68: after decompression, 0 for tEXt/zTXt jpayne@68: text_ptr[i].lang - language of comment (NULL or jpayne@68: empty for unknown). jpayne@68: text_ptr[i].translated_keyword - keyword in UTF-8 (NULL jpayne@68: or empty for unknown). jpayne@68: jpayne@68: Note that the itxt_length, lang, and lang_key jpayne@68: members of the text_ptr structure only exist when the jpayne@68: library is built with iTXt chunk support. Prior to jpayne@68: libpng-1.4.0 the library was built by default without jpayne@68: iTXt support. Also note that when iTXt is supported, jpayne@68: they contain NULL pointers when the "compression" jpayne@68: field contains PNG_TEXT_COMPRESSION_NONE or jpayne@68: PNG_TEXT_COMPRESSION_zTXt. jpayne@68: jpayne@68: num_text - number of comments jpayne@68: jpayne@68: png_set_sPLT(png_ptr, info_ptr, &palette_ptr, jpayne@68: num_spalettes); jpayne@68: jpayne@68: palette_ptr - array of png_sPLT_struct structures jpayne@68: to be added to the list of palettes jpayne@68: in the info structure. jpayne@68: num_spalettes - number of palette structures to be jpayne@68: added. jpayne@68: jpayne@68: png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y, jpayne@68: unit_type); jpayne@68: jpayne@68: offset_x - positive offset from the left jpayne@68: edge of the screen jpayne@68: jpayne@68: offset_y - positive offset from the top jpayne@68: edge of the screen jpayne@68: jpayne@68: unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER jpayne@68: jpayne@68: png_set_pHYs(png_ptr, info_ptr, res_x, res_y, jpayne@68: unit_type); jpayne@68: jpayne@68: res_x - pixels/unit physical resolution jpayne@68: in x direction jpayne@68: jpayne@68: res_y - pixels/unit physical resolution jpayne@68: in y direction jpayne@68: jpayne@68: unit_type - PNG_RESOLUTION_UNKNOWN, jpayne@68: PNG_RESOLUTION_METER jpayne@68: jpayne@68: png_set_sCAL(png_ptr, info_ptr, unit, width, height) jpayne@68: jpayne@68: unit - physical scale units (an integer) jpayne@68: jpayne@68: width - width of a pixel in physical scale units jpayne@68: jpayne@68: height - height of a pixel in physical scale units jpayne@68: (width and height are doubles) jpayne@68: jpayne@68: png_set_sCAL_s(png_ptr, info_ptr, unit, width, height) jpayne@68: jpayne@68: unit - physical scale units (an integer) jpayne@68: jpayne@68: width - width of a pixel in physical scale units jpayne@68: expressed as a string jpayne@68: jpayne@68: height - height of a pixel in physical scale units jpayne@68: (width and height are strings like "2.54") jpayne@68: jpayne@68: png_set_unknown_chunks(png_ptr, info_ptr, &unknowns, jpayne@68: num_unknowns) jpayne@68: jpayne@68: unknowns - array of png_unknown_chunk jpayne@68: structures holding unknown chunks jpayne@68: unknowns[i].name - name of unknown chunk jpayne@68: unknowns[i].data - data of unknown chunk jpayne@68: unknowns[i].size - size of unknown chunk's data jpayne@68: unknowns[i].location - position to write chunk in file jpayne@68: 0: do not write chunk jpayne@68: PNG_HAVE_IHDR: before PLTE jpayne@68: PNG_HAVE_PLTE: before IDAT jpayne@68: PNG_AFTER_IDAT: after IDAT jpayne@68: jpayne@68: The "location" member is set automatically according to jpayne@68: what part of the output file has already been written. jpayne@68: You can change its value after calling png_set_unknown_chunks() jpayne@68: as demonstrated in pngtest.c. Within each of the "locations", jpayne@68: the chunks are sequenced according to their position in the jpayne@68: structure (that is, the value of "i", which is the order in which jpayne@68: the chunk was either read from the input file or defined with jpayne@68: png_set_unknown_chunks). jpayne@68: jpayne@68: A quick word about text and num_text. text is an array of png_text jpayne@68: structures. num_text is the number of valid structures in the array. jpayne@68: Each png_text structure holds a language code, a keyword, a text value, jpayne@68: and a compression type. jpayne@68: jpayne@68: The compression types have the same valid numbers as the compression jpayne@68: types of the image data. Currently, the only valid number is zero. jpayne@68: However, you can store text either compressed or uncompressed, unlike jpayne@68: images, which always have to be compressed. So if you don't want the jpayne@68: text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE. jpayne@68: Because tEXt and zTXt chunks don't have a language field, if you jpayne@68: specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt jpayne@68: any language code or translated keyword will not be written out. jpayne@68: jpayne@68: Until text gets around a few hundred bytes, it is not worth compressing it. jpayne@68: After the text has been written out to the file, the compression type jpayne@68: is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR, jpayne@68: so that it isn't written out again at the end (in case you are calling jpayne@68: png_write_end() with the same struct). jpayne@68: jpayne@68: The keywords that are given in the PNG Specification are: jpayne@68: jpayne@68: Title Short (one line) title or jpayne@68: caption for image jpayne@68: jpayne@68: Author Name of image's creator jpayne@68: jpayne@68: Description Description of image (possibly long) jpayne@68: jpayne@68: Copyright Copyright notice jpayne@68: jpayne@68: Creation Time Time of original image creation jpayne@68: (usually RFC 1123 format, see below) jpayne@68: jpayne@68: Software Software used to create the image jpayne@68: jpayne@68: Disclaimer Legal disclaimer jpayne@68: jpayne@68: Warning Warning of nature of content jpayne@68: jpayne@68: Source Device used to create the image jpayne@68: jpayne@68: Comment Miscellaneous comment; conversion jpayne@68: from other image format jpayne@68: jpayne@68: The keyword-text pairs work like this. Keywords should be short jpayne@68: simple descriptions of what the comment is about. Some typical jpayne@68: keywords are found in the PNG specification, as is some recommendations jpayne@68: on keywords. You can repeat keywords in a file. You can even write jpayne@68: some text before the image and some after. For example, you may want jpayne@68: to put a description of the image before the image, but leave the jpayne@68: disclaimer until after, so viewers working over modem connections jpayne@68: don't have to wait for the disclaimer to go over the modem before jpayne@68: they start seeing the image. Finally, keywords should be full jpayne@68: words, not abbreviations. Keywords and text are in the ISO 8859-1 jpayne@68: (Latin-1) character set (a superset of regular ASCII) and can not jpayne@68: contain NUL characters, and should not contain control or other jpayne@68: unprintable characters. To make the comments widely readable, stick jpayne@68: with basic ASCII, and avoid machine specific character set extensions jpayne@68: like the IBM-PC character set. The keyword must be present, but jpayne@68: you can leave off the text string on non-compressed pairs. jpayne@68: Compressed pairs must have a text string, as only the text string jpayne@68: is compressed anyway, so the compression would be meaningless. jpayne@68: jpayne@68: PNG supports modification time via the png_time structure. Two jpayne@68: conversion routines are provided, png_convert_from_time_t() for jpayne@68: time_t and png_convert_from_struct_tm() for struct tm. The jpayne@68: time_t routine uses gmtime(). You don't have to use either of jpayne@68: these, but if you wish to fill in the png_time structure directly, jpayne@68: you should provide the time in universal time (GMT) if possible jpayne@68: instead of your local time. Note that the year number is the full jpayne@68: year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and jpayne@68: that months start with 1. jpayne@68: jpayne@68: If you want to store the time of the original image creation, you should jpayne@68: use a plain tEXt chunk with the "Creation Time" keyword. This is jpayne@68: necessary because the "creation time" of a PNG image is somewhat vague, jpayne@68: depending on whether you mean the PNG file, the time the image was jpayne@68: created in a non-PNG format, a still photo from which the image was jpayne@68: scanned, or possibly the subject matter itself. In order to facilitate jpayne@68: machine-readable dates, it is recommended that the "Creation Time" jpayne@68: tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"), jpayne@68: although this isn't a requirement. Unlike the tIME chunk, the jpayne@68: "Creation Time" tEXt chunk is not expected to be automatically changed jpayne@68: by the software. To facilitate the use of RFC 1123 dates, a function jpayne@68: png_convert_to_rfc1123_buffer(buffer, png_timep) is provided to jpayne@68: convert from PNG time to an RFC 1123 format string. The caller must provide jpayne@68: a writeable buffer of at least 29 bytes. jpayne@68: jpayne@68: .SS Writing unknown chunks jpayne@68: jpayne@68: You can use the png_set_unknown_chunks function to queue up private chunks jpayne@68: for writing. You give it a chunk name, location, raw data, and a size. You jpayne@68: also must use png_set_keep_unknown_chunks() to ensure that libpng will jpayne@68: handle them. That's all there is to it. The chunks will be written by the jpayne@68: next following png_write_info_before_PLTE, png_write_info, or png_write_end jpayne@68: function, depending upon the specified location. Any chunks previously jpayne@68: read into the info structure's unknown-chunk list will also be written out jpayne@68: in a sequence that satisfies the PNG specification's ordering rules. jpayne@68: jpayne@68: Here is an example of writing two private chunks, prVt and miNE: jpayne@68: jpayne@68: #ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED jpayne@68: /* Set unknown chunk data */ jpayne@68: png_unknown_chunk unk_chunk[2]; jpayne@68: strcpy((char *) unk_chunk[0].name, "prVt"; jpayne@68: unk_chunk[0].data = (unsigned char *) "PRIVATE DATA"; jpayne@68: unk_chunk[0].size = strlen(unk_chunk[0].data)+1; jpayne@68: unk_chunk[0].location = PNG_HAVE_IHDR; jpayne@68: strcpy((char *) unk_chunk[1].name, "miNE"; jpayne@68: unk_chunk[1].data = (unsigned char *) "MY CHUNK DATA"; jpayne@68: unk_chunk[1].size = strlen(unk_chunk[0].data)+1; jpayne@68: unk_chunk[1].location = PNG_AFTER_IDAT; jpayne@68: png_set_unknown_chunks(write_ptr, write_info_ptr, jpayne@68: unk_chunk, 2); jpayne@68: /* Needed because miNE is not safe-to-copy */ jpayne@68: png_set_keep_unknown_chunks(png, PNG_HANDLE_CHUNK_ALWAYS, jpayne@68: (png_bytep) "miNE", 1); jpayne@68: # if PNG_LIBPNG_VER < 10600 jpayne@68: /* Deal with unknown chunk location bug in 1.5.x and earlier */ jpayne@68: png_set_unknown_chunk_location(png, info, 0, PNG_HAVE_IHDR); jpayne@68: png_set_unknown_chunk_location(png, info, 1, PNG_AFTER_IDAT); jpayne@68: # endif jpayne@68: # if PNG_LIBPNG_VER < 10500 jpayne@68: /* PNG_AFTER_IDAT writes two copies of the chunk prior to libpng-1.5.0, jpayne@68: * one before IDAT and another after IDAT, so don't use it; only use jpayne@68: * PNG_HAVE_IHDR location. This call resets the location previously jpayne@68: * set by assignment and png_set_unknown_chunk_location() for chunk 1. jpayne@68: */ jpayne@68: png_set_unknown_chunk_location(png, info, 1, PNG_HAVE_IHDR); jpayne@68: # endif jpayne@68: #endif jpayne@68: jpayne@68: .SS The high-level write interface jpayne@68: jpayne@68: At this point there are two ways to proceed; through the high-level jpayne@68: write interface, or through a sequence of low-level write operations. jpayne@68: You can use the high-level interface if your image data is present jpayne@68: in the info structure. All defined output jpayne@68: transformations are permitted, enabled by the following masks. jpayne@68: jpayne@68: PNG_TRANSFORM_IDENTITY No transformation jpayne@68: PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples jpayne@68: PNG_TRANSFORM_PACKSWAP Change order of packed jpayne@68: pixels to LSB first jpayne@68: PNG_TRANSFORM_INVERT_MONO Invert monochrome images jpayne@68: PNG_TRANSFORM_SHIFT Normalize pixels to the jpayne@68: sBIT depth jpayne@68: PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA jpayne@68: to BGRA jpayne@68: PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA jpayne@68: to AG jpayne@68: PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity jpayne@68: to transparency jpayne@68: PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples jpayne@68: PNG_TRANSFORM_STRIP_FILLER Strip out filler jpayne@68: bytes (deprecated). jpayne@68: PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading jpayne@68: filler bytes jpayne@68: PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing jpayne@68: filler bytes jpayne@68: jpayne@68: If you have valid image data in the info structure (you can use jpayne@68: png_set_rows() to put image data in the info structure), simply do this: jpayne@68: jpayne@68: png_write_png(png_ptr, info_ptr, png_transforms, NULL) jpayne@68: jpayne@68: where png_transforms is an integer containing the bitwise OR of some set of jpayne@68: transformation flags. This call is equivalent to png_write_info(), jpayne@68: followed the set of transformations indicated by the transform mask, jpayne@68: then png_write_image(), and finally png_write_end(). jpayne@68: jpayne@68: (The final parameter of this call is not yet used. Someday it might point jpayne@68: to transformation parameters required by some future output transform.) jpayne@68: jpayne@68: You must use png_transforms and not call any png_set_transform() functions jpayne@68: when you use png_write_png(). jpayne@68: jpayne@68: .SS The low-level write interface jpayne@68: jpayne@68: If you are going the low-level route instead, you are now ready to jpayne@68: write all the file information up to the actual image data. You do jpayne@68: this with a call to png_write_info(). jpayne@68: jpayne@68: png_write_info(png_ptr, info_ptr); jpayne@68: jpayne@68: Note that there is one transformation you may need to do before jpayne@68: png_write_info(). In PNG files, the alpha channel in an image is the jpayne@68: level of opacity. If your data is supplied as a level of transparency, jpayne@68: you can invert the alpha channel before you write it, so that 0 is jpayne@68: fully transparent and 255 (in 8-bit or paletted images) or 65535 jpayne@68: (in 16-bit images) is fully opaque, with jpayne@68: jpayne@68: png_set_invert_alpha(png_ptr); jpayne@68: jpayne@68: This must appear before png_write_info() instead of later with the jpayne@68: other transformations because in the case of paletted images the tRNS jpayne@68: chunk data has to be inverted before the tRNS chunk is written. If jpayne@68: your image is not a paletted image, the tRNS data (which in such cases jpayne@68: represents a single color to be rendered as transparent) won't need to jpayne@68: be changed, and you can safely do this transformation after your jpayne@68: png_write_info() call. jpayne@68: jpayne@68: If you need to write a private chunk that you want to appear before jpayne@68: the PLTE chunk when PLTE is present, you can write the PNG info in jpayne@68: two steps, and insert code to write your own chunk between them: jpayne@68: jpayne@68: png_write_info_before_PLTE(png_ptr, info_ptr); jpayne@68: png_set_unknown_chunks(png_ptr, info_ptr, ...); jpayne@68: png_write_info(png_ptr, info_ptr); jpayne@68: jpayne@68: After you've written the file information, you can set up the library jpayne@68: to handle any special transformations of the image data. The various jpayne@68: ways to transform the data will be described in the order that they jpayne@68: should occur. This is important, as some of these change the color jpayne@68: type and/or bit depth of the data, and some others only work on jpayne@68: certain color types and bit depths. Even though each transformation jpayne@68: checks to see if it has data that it can do something with, you should jpayne@68: make sure to only enable a transformation if it will be valid for the jpayne@68: data. For example, don't swap red and blue on grayscale data. jpayne@68: jpayne@68: PNG files store RGB pixels packed into 3 or 6 bytes. This code tells jpayne@68: the library to strip input data that has 4 or 8 bytes per pixel down jpayne@68: to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2 jpayne@68: bytes per pixel). jpayne@68: jpayne@68: png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE); jpayne@68: jpayne@68: where the 0 is unused, and the location is either PNG_FILLER_BEFORE or jpayne@68: PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel jpayne@68: is stored XRGB or RGBX. jpayne@68: jpayne@68: PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as jpayne@68: they can, resulting in, for example, 8 pixels per byte for 1 bit files. jpayne@68: If the data is supplied at 1 pixel per byte, use this code, which will jpayne@68: correctly pack the pixels into a single byte: jpayne@68: jpayne@68: png_set_packing(png_ptr); jpayne@68: jpayne@68: PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your jpayne@68: data is of another bit depth, you can write an sBIT chunk into the jpayne@68: file so that decoders can recover the original data if desired. jpayne@68: jpayne@68: /* Set the true bit depth of the image data */ jpayne@68: if (color_type & PNG_COLOR_MASK_COLOR) jpayne@68: { jpayne@68: sig_bit.red = true_bit_depth; jpayne@68: sig_bit.green = true_bit_depth; jpayne@68: sig_bit.blue = true_bit_depth; jpayne@68: } jpayne@68: jpayne@68: else jpayne@68: { jpayne@68: sig_bit.gray = true_bit_depth; jpayne@68: } jpayne@68: jpayne@68: if (color_type & PNG_COLOR_MASK_ALPHA) jpayne@68: { jpayne@68: sig_bit.alpha = true_bit_depth; jpayne@68: } jpayne@68: jpayne@68: png_set_sBIT(png_ptr, info_ptr, &sig_bit); jpayne@68: jpayne@68: If the data is stored in the row buffer in a bit depth other than jpayne@68: one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG), jpayne@68: this will scale the values to appear to be the correct bit depth as jpayne@68: is required by PNG. jpayne@68: jpayne@68: png_set_shift(png_ptr, &sig_bit); jpayne@68: jpayne@68: PNG files store 16-bit pixels in network byte order (big-endian, jpayne@68: ie. most significant bits first). This code would be used if they are jpayne@68: supplied the other way (little-endian, i.e. least significant bits jpayne@68: first, the way PCs store them): jpayne@68: jpayne@68: if (bit_depth > 8) jpayne@68: png_set_swap(png_ptr); jpayne@68: jpayne@68: If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you jpayne@68: need to change the order the pixels are packed into bytes, you can use: jpayne@68: jpayne@68: if (bit_depth < 8) jpayne@68: png_set_packswap(png_ptr); jpayne@68: jpayne@68: PNG files store 3 color pixels in red, green, blue order. This code jpayne@68: would be used if they are supplied as blue, green, red: jpayne@68: jpayne@68: png_set_bgr(png_ptr); jpayne@68: jpayne@68: PNG files describe monochrome as black being zero and white being jpayne@68: one. This code would be used if the pixels are supplied with this reversed jpayne@68: (black being one and white being zero): jpayne@68: jpayne@68: png_set_invert_mono(png_ptr); jpayne@68: jpayne@68: Finally, you can write your own transformation function if none of jpayne@68: the existing ones meets your needs. This is done by setting a callback jpayne@68: with jpayne@68: jpayne@68: png_set_write_user_transform_fn(png_ptr, jpayne@68: write_transform_fn); jpayne@68: jpayne@68: You must supply the function jpayne@68: jpayne@68: void write_transform_fn(png_structp png_ptr, png_row_infop jpayne@68: row_info, png_bytep data) jpayne@68: jpayne@68: See pngtest.c for a working example. Your function will be called jpayne@68: before any of the other transformations are processed. If supported jpayne@68: libpng also supplies an information routine that may be called from jpayne@68: your callback: jpayne@68: jpayne@68: png_get_current_row_number(png_ptr); jpayne@68: png_get_current_pass_number(png_ptr); jpayne@68: jpayne@68: This returns the current row passed to the transform. With interlaced jpayne@68: images the value returned is the row in the input sub-image image. Use jpayne@68: PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to jpayne@68: find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass). jpayne@68: jpayne@68: The discussion of interlace handling above contains more information on how to jpayne@68: use these values. jpayne@68: jpayne@68: You can also set up a pointer to a user structure for use by your jpayne@68: callback function. jpayne@68: jpayne@68: png_set_user_transform_info(png_ptr, user_ptr, 0, 0); jpayne@68: jpayne@68: The user_channels and user_depth parameters of this function are ignored jpayne@68: when writing; you can set them to zero as shown. jpayne@68: jpayne@68: You can retrieve the pointer via the function png_get_user_transform_ptr(). jpayne@68: For example: jpayne@68: jpayne@68: voidp write_user_transform_ptr = jpayne@68: png_get_user_transform_ptr(png_ptr); jpayne@68: jpayne@68: It is possible to have libpng flush any pending output, either manually, jpayne@68: or automatically after a certain number of lines have been written. To jpayne@68: flush the output stream a single time call: jpayne@68: jpayne@68: png_write_flush(png_ptr); jpayne@68: jpayne@68: and to have libpng flush the output stream periodically after a certain jpayne@68: number of scanlines have been written, call: jpayne@68: jpayne@68: png_set_flush(png_ptr, nrows); jpayne@68: jpayne@68: Note that the distance between rows is from the last time png_write_flush() jpayne@68: was called, or the first row of the image if it has never been called. jpayne@68: So if you write 50 lines, and then png_set_flush 25, it will flush the jpayne@68: output on the next scanline, and every 25 lines thereafter, unless jpayne@68: png_write_flush() is called before 25 more lines have been written. jpayne@68: If nrows is too small (less than about 10 lines for a 640 pixel wide jpayne@68: RGB image) the image compression may decrease noticeably (although this jpayne@68: may be acceptable for real-time applications). Infrequent flushing will jpayne@68: only degrade the compression performance by a few percent over images jpayne@68: that do not use flushing. jpayne@68: jpayne@68: .SS Writing the image data jpayne@68: jpayne@68: That's it for the transformations. Now you can write the image data. jpayne@68: The simplest way to do this is in one function call. If you have the jpayne@68: whole image in memory, you can just call png_write_image() and libpng jpayne@68: will write the image. You will need to pass in an array of pointers to jpayne@68: each row. This function automatically handles interlacing, so you don't jpayne@68: need to call png_set_interlace_handling() or call this function multiple jpayne@68: times, or any of that other stuff necessary with png_write_rows(). jpayne@68: jpayne@68: png_write_image(png_ptr, row_pointers); jpayne@68: jpayne@68: where row_pointers is: jpayne@68: jpayne@68: png_byte *row_pointers[height]; jpayne@68: jpayne@68: You can point to void or char or whatever you use for pixels. jpayne@68: jpayne@68: If you don't want to write the whole image at once, you can jpayne@68: use png_write_rows() instead. If the file is not interlaced, jpayne@68: this is simple: jpayne@68: jpayne@68: png_write_rows(png_ptr, row_pointers, jpayne@68: number_of_rows); jpayne@68: jpayne@68: row_pointers is the same as in the png_write_image() call. jpayne@68: jpayne@68: If you are just writing one row at a time, you can do this with jpayne@68: a single row_pointer instead of an array of row_pointers: jpayne@68: jpayne@68: png_bytep row_pointer = row; jpayne@68: jpayne@68: png_write_row(png_ptr, row_pointer); jpayne@68: jpayne@68: When the file is interlaced, things can get a good deal more complicated. jpayne@68: The only currently (as of the PNG Specification version 1.2, dated July jpayne@68: 1999) defined interlacing scheme for PNG files is the "Adam7" interlace jpayne@68: scheme, that breaks down an image into seven smaller images of varying jpayne@68: size. libpng will build these images for you, or you can do them jpayne@68: yourself. If you want to build them yourself, see the PNG specification jpayne@68: for details of which pixels to write when. jpayne@68: jpayne@68: If you don't want libpng to handle the interlacing details, just jpayne@68: use png_set_interlace_handling() and call png_write_rows() the jpayne@68: correct number of times to write all the sub-images jpayne@68: (png_set_interlace_handling() returns the number of sub-images.) jpayne@68: jpayne@68: If you want libpng to build the sub-images, call this before you start jpayne@68: writing any rows: jpayne@68: jpayne@68: number_of_passes = png_set_interlace_handling(png_ptr); jpayne@68: jpayne@68: This will return the number of passes needed. Currently, this is seven, jpayne@68: but may change if another interlace type is added. jpayne@68: jpayne@68: Then write the complete image number_of_passes times. jpayne@68: jpayne@68: png_write_rows(png_ptr, row_pointers, number_of_rows); jpayne@68: jpayne@68: Think carefully before you write an interlaced image. Typically code that jpayne@68: reads such images reads all the image data into memory, uncompressed, before jpayne@68: doing any processing. Only code that can display an image on the fly can jpayne@68: take advantage of the interlacing and even then the image has to be exactly jpayne@68: the correct size for the output device, because scaling an image requires jpayne@68: adjacent pixels and these are not available until all the passes have been jpayne@68: read. jpayne@68: jpayne@68: If you do write an interlaced image you will hardly ever need to handle jpayne@68: the interlacing yourself. Call png_set_interlace_handling() and use the jpayne@68: approach described above. jpayne@68: jpayne@68: The only time it is conceivable that you will really need to write an jpayne@68: interlaced image pass-by-pass is when you have read one pass by pass and jpayne@68: made some pixel-by-pixel transformation to it, as described in the read jpayne@68: code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros jpayne@68: to determine the size of each sub-image in turn and simply write the rows jpayne@68: you obtained from the read code. jpayne@68: jpayne@68: .SS Finishing a sequential write jpayne@68: jpayne@68: After you are finished writing the image, you should finish writing jpayne@68: the file. If you are interested in writing comments or time, you should jpayne@68: pass an appropriately filled png_info pointer. If you are not interested, jpayne@68: you can pass NULL. jpayne@68: jpayne@68: png_write_end(png_ptr, info_ptr); jpayne@68: jpayne@68: When you are done, you can free all memory used by libpng like this: jpayne@68: jpayne@68: png_destroy_write_struct(&png_ptr, &info_ptr); jpayne@68: jpayne@68: It is also possible to individually free the info_ptr members that jpayne@68: point to libpng-allocated storage with the following function: jpayne@68: jpayne@68: png_free_data(png_ptr, info_ptr, mask, seq) jpayne@68: jpayne@68: mask - identifies data to be freed, a mask jpayne@68: containing the bitwise OR of one or jpayne@68: more of jpayne@68: PNG_FREE_PLTE, PNG_FREE_TRNS, jpayne@68: PNG_FREE_HIST, PNG_FREE_ICCP, jpayne@68: PNG_FREE_PCAL, PNG_FREE_ROWS, jpayne@68: PNG_FREE_SCAL, PNG_FREE_SPLT, jpayne@68: PNG_FREE_TEXT, PNG_FREE_UNKN, jpayne@68: or simply PNG_FREE_ALL jpayne@68: jpayne@68: seq - sequence number of item to be freed jpayne@68: (\-1 for all items) jpayne@68: jpayne@68: This function may be safely called when the relevant storage has jpayne@68: already been freed, or has not yet been allocated, or was allocated jpayne@68: by the user and not by libpng, and will in those cases do nothing. jpayne@68: The "seq" parameter is ignored if only one item of the selected data jpayne@68: type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items jpayne@68: are allowed for the data type identified in the mask, such as text or jpayne@68: sPLT, only the n'th item in the structure is freed, where n is "seq". jpayne@68: jpayne@68: If you allocated data such as a palette that you passed in to libpng jpayne@68: with png_set_*, you must not free it until just before the call to jpayne@68: png_destroy_write_struct(). jpayne@68: jpayne@68: The default behavior is only to free data that was allocated internally jpayne@68: by libpng. This can be changed, so that libpng will not free the data, jpayne@68: or so that it will free data that was allocated by the user with png_malloc() jpayne@68: or png_calloc() and passed in via a png_set_*() function, with jpayne@68: jpayne@68: png_data_freer(png_ptr, info_ptr, freer, mask) jpayne@68: jpayne@68: freer - one of jpayne@68: PNG_DESTROY_WILL_FREE_DATA jpayne@68: PNG_SET_WILL_FREE_DATA jpayne@68: PNG_USER_WILL_FREE_DATA jpayne@68: jpayne@68: mask - which data elements are affected jpayne@68: same choices as in png_free_data() jpayne@68: jpayne@68: For example, to transfer responsibility for some data from a read structure jpayne@68: to a write structure, you could use jpayne@68: jpayne@68: png_data_freer(read_ptr, read_info_ptr, jpayne@68: PNG_USER_WILL_FREE_DATA, jpayne@68: PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST) jpayne@68: jpayne@68: png_data_freer(write_ptr, write_info_ptr, jpayne@68: PNG_DESTROY_WILL_FREE_DATA, jpayne@68: PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST) jpayne@68: jpayne@68: thereby briefly reassigning responsibility for freeing to the user but jpayne@68: immediately afterwards reassigning it once more to the write_destroy jpayne@68: function. Having done this, it would then be safe to destroy the read jpayne@68: structure and continue to use the PLTE, tRNS, and hIST data in the write jpayne@68: structure. jpayne@68: jpayne@68: This function only affects data that has already been allocated. jpayne@68: You can call this function before calling after the png_set_*() functions jpayne@68: to control whether the user or png_destroy_*() is supposed to free the data. jpayne@68: When the user assumes responsibility for libpng-allocated data, the jpayne@68: application must use jpayne@68: png_free() to free it, and when the user transfers responsibility to libpng jpayne@68: for data that the user has allocated, the user must have used png_malloc() jpayne@68: or png_calloc() to allocate it. jpayne@68: jpayne@68: If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword jpayne@68: separately, do not transfer responsibility for freeing text_ptr to libpng, jpayne@68: because when libpng fills a png_text structure it combines these members with jpayne@68: the key member, and png_free_data() will free only text_ptr.key. Similarly, jpayne@68: if you transfer responsibility for free'ing text_ptr from libpng to your jpayne@68: application, your application must not separately free those members. jpayne@68: For a more compact example of writing a PNG image, see the file example.c. jpayne@68: jpayne@68: .SH V. Simplified API jpayne@68: jpayne@68: The simplified API, which became available in libpng-1.6.0, hides the details jpayne@68: of both libpng and the PNG file format itself. jpayne@68: It allows PNG files to be read into a very limited number of jpayne@68: in-memory bitmap formats or to be written from the same formats. If these jpayne@68: formats do not accommodate your needs then you can, and should, use the more jpayne@68: sophisticated APIs above - these support a wide variety of in-memory formats jpayne@68: and a wide variety of sophisticated transformations to those formats as well jpayne@68: as a wide variety of APIs to manipulate ancillary information. jpayne@68: jpayne@68: To read a PNG file using the simplified API: jpayne@68: jpayne@68: 1) Declare a 'png_image' structure (see below) on the stack, set the jpayne@68: version field to PNG_IMAGE_VERSION and the 'opaque' pointer to NULL jpayne@68: (this is REQUIRED, your program may crash if you don't do it.) jpayne@68: jpayne@68: 2) Call the appropriate png_image_begin_read... function. jpayne@68: jpayne@68: 3) Set the png_image 'format' member to the required sample format. jpayne@68: jpayne@68: 4) Allocate a buffer for the image and, if required, the color-map. jpayne@68: jpayne@68: 5) Call png_image_finish_read to read the image and, if required, the jpayne@68: color-map into your buffers. jpayne@68: jpayne@68: There are no restrictions on the format of the PNG input itself; all valid jpayne@68: color types, bit depths, and interlace methods are acceptable, and the jpayne@68: input image is transformed as necessary to the requested in-memory format jpayne@68: during the png_image_finish_read() step. The only caveat is that if you jpayne@68: request a color-mapped image from a PNG that is full-color or makes jpayne@68: complex use of an alpha channel the transformation is extremely lossy and the jpayne@68: result may look terrible. jpayne@68: jpayne@68: To write a PNG file using the simplified API: jpayne@68: jpayne@68: 1) Declare a 'png_image' structure on the stack and memset() jpayne@68: it to all zero. jpayne@68: jpayne@68: 2) Initialize the members of the structure that describe the jpayne@68: image, setting the 'format' member to the format of the jpayne@68: image samples. jpayne@68: jpayne@68: 3) Call the appropriate png_image_write... function with a jpayne@68: pointer to the image and, if necessary, the color-map to write jpayne@68: the PNG data. jpayne@68: jpayne@68: png_image is a structure that describes the in-memory format of an image jpayne@68: when it is being read or defines the in-memory format of an image that you jpayne@68: need to write. The "png_image" structure contains the following members: jpayne@68: jpayne@68: png_controlp opaque Initialize to NULL, free with png_image_free jpayne@68: png_uint_32 version Set to PNG_IMAGE_VERSION jpayne@68: png_uint_32 width Image width in pixels (columns) jpayne@68: png_uint_32 height Image height in pixels (rows) jpayne@68: png_uint_32 format Image format as defined below jpayne@68: png_uint_32 flags A bit mask containing informational flags jpayne@68: png_uint_32 colormap_entries; Number of entries in the color-map jpayne@68: png_uint_32 warning_or_error; jpayne@68: char message[64]; jpayne@68: jpayne@68: In the event of an error or warning the "warning_or_error" jpayne@68: field will be set to a non-zero value and the 'message' field will contain jpayne@68: a '\0' terminated string with the libpng error or warning message. If both jpayne@68: warnings and an error were encountered, only the error is recorded. If there jpayne@68: are multiple warnings, only the first one is recorded. jpayne@68: jpayne@68: The upper 30 bits of the "warning_or_error" value are reserved; the low two jpayne@68: bits contain a two bit code such that a value more than 1 indicates a failure jpayne@68: in the API just called: jpayne@68: jpayne@68: 0 - no warning or error jpayne@68: 1 - warning jpayne@68: 2 - error jpayne@68: 3 - error preceded by warning jpayne@68: jpayne@68: The pixels (samples) of the image have one to four channels whose components jpayne@68: have original values in the range 0 to 1.0: jpayne@68: jpayne@68: 1: A single gray or luminance channel (G). jpayne@68: 2: A gray/luminance channel and an alpha channel (GA). jpayne@68: 3: Three red, green, blue color channels (RGB). jpayne@68: 4: Three color channels and an alpha channel (RGBA). jpayne@68: jpayne@68: The channels are encoded in one of two ways: jpayne@68: jpayne@68: a) As a small integer, value 0..255, contained in a single byte. For the jpayne@68: alpha channel the original value is simply value/255. For the color or jpayne@68: luminance channels the value is encoded according to the sRGB specification jpayne@68: and matches the 8-bit format expected by typical display devices. jpayne@68: jpayne@68: The color/gray channels are not scaled (pre-multiplied) by the alpha jpayne@68: channel and are suitable for passing to color management software. jpayne@68: jpayne@68: b) As a value in the range 0..65535, contained in a 2-byte integer, in jpayne@68: the native byte order of the platform on which the application is running. jpayne@68: All channels can be converted to the original value by dividing by 65535; all jpayne@68: channels are linear. Color channels use the RGB encoding (RGB end-points) of jpayne@68: the sRGB specification. This encoding is identified by the jpayne@68: PNG_FORMAT_FLAG_LINEAR flag below. jpayne@68: jpayne@68: When the simplified API needs to convert between sRGB and linear colorspaces, jpayne@68: the actual sRGB transfer curve defined in the sRGB specification (see the jpayne@68: article at https://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2 jpayne@68: approximation used elsewhere in libpng. jpayne@68: jpayne@68: When an alpha channel is present it is expected to denote pixel coverage jpayne@68: of the color or luminance channels and is returned as an associated alpha jpayne@68: channel: the color/gray channels are scaled (pre-multiplied) by the alpha jpayne@68: value. jpayne@68: jpayne@68: The samples are either contained directly in the image data, between 1 and 8 jpayne@68: bytes per pixel according to the encoding, or are held in a color-map indexed jpayne@68: by bytes in the image data. In the case of a color-map the color-map entries jpayne@68: are individual samples, encoded as above, and the image data has one byte per jpayne@68: pixel to select the relevant sample from the color-map. jpayne@68: jpayne@68: PNG_FORMAT_* jpayne@68: jpayne@68: The #defines to be used in png_image::format. Each #define identifies a jpayne@68: particular layout of channel data and, if present, alpha values. There are jpayne@68: separate defines for each of the two component encodings. jpayne@68: jpayne@68: A format is built up using single bit flag values. All combinations are jpayne@68: valid. Formats can be built up from the flag values or you can use one of jpayne@68: the predefined values below. When testing formats always use the FORMAT_FLAG jpayne@68: macros to test for individual features - future versions of the library may jpayne@68: add new flags. jpayne@68: jpayne@68: When reading or writing color-mapped images the format should be set to the jpayne@68: format of the entries in the color-map then png_image_{read,write}_colormap jpayne@68: called to read or write the color-map and set the format correctly for the jpayne@68: image data. Do not set the PNG_FORMAT_FLAG_COLORMAP bit directly! jpayne@68: jpayne@68: NOTE: libpng can be built with particular features disabled. If you see jpayne@68: compiler errors because the definition of one of the following flags has been jpayne@68: compiled out it is because libpng does not have the required support. It is jpayne@68: possible, however, for the libpng configuration to enable the format on just jpayne@68: read or just write; in that case you may see an error at run time. jpayne@68: You can guard against this by checking for the definition of the jpayne@68: appropriate "_SUPPORTED" macro, one of: jpayne@68: jpayne@68: PNG_SIMPLIFIED_{READ,WRITE}_{BGR,AFIRST}_SUPPORTED jpayne@68: jpayne@68: PNG_FORMAT_FLAG_ALPHA format with an alpha channel jpayne@68: PNG_FORMAT_FLAG_COLOR color format: otherwise grayscale jpayne@68: PNG_FORMAT_FLAG_LINEAR 2-byte channels else 1-byte jpayne@68: PNG_FORMAT_FLAG_COLORMAP image data is color-mapped jpayne@68: PNG_FORMAT_FLAG_BGR BGR colors, else order is RGB jpayne@68: PNG_FORMAT_FLAG_AFIRST alpha channel comes first jpayne@68: jpayne@68: Supported formats are as follows. Future versions of libpng may support more jpayne@68: formats; for compatibility with older versions simply check if the format jpayne@68: macro is defined using #ifdef. These defines describe the in-memory layout jpayne@68: of the components of the pixels of the image. jpayne@68: jpayne@68: First the single byte (sRGB) formats: jpayne@68: jpayne@68: PNG_FORMAT_GRAY jpayne@68: PNG_FORMAT_GA jpayne@68: PNG_FORMAT_AG jpayne@68: PNG_FORMAT_RGB jpayne@68: PNG_FORMAT_BGR jpayne@68: PNG_FORMAT_RGBA jpayne@68: PNG_FORMAT_ARGB jpayne@68: PNG_FORMAT_BGRA jpayne@68: PNG_FORMAT_ABGR jpayne@68: jpayne@68: Then the linear 2-byte formats. When naming these "Y" is used to jpayne@68: indicate a luminance (gray) channel. The component order within the pixel jpayne@68: is always the same - there is no provision for swapping the order of the jpayne@68: components in the linear format. The components are 16-bit integers in jpayne@68: the native byte order for your platform, and there is no provision for jpayne@68: swapping the bytes to a different endian condition. jpayne@68: jpayne@68: PNG_FORMAT_LINEAR_Y jpayne@68: PNG_FORMAT_LINEAR_Y_ALPHA jpayne@68: PNG_FORMAT_LINEAR_RGB jpayne@68: PNG_FORMAT_LINEAR_RGB_ALPHA jpayne@68: jpayne@68: With color-mapped formats the image data is one byte for each pixel. The byte jpayne@68: is an index into the color-map which is formatted as above. To obtain a jpayne@68: color-mapped format it is sufficient just to add the PNG_FOMAT_FLAG_COLORMAP jpayne@68: to one of the above definitions, or you can use one of the definitions below. jpayne@68: jpayne@68: PNG_FORMAT_RGB_COLORMAP jpayne@68: PNG_FORMAT_BGR_COLORMAP jpayne@68: PNG_FORMAT_RGBA_COLORMAP jpayne@68: PNG_FORMAT_ARGB_COLORMAP jpayne@68: PNG_FORMAT_BGRA_COLORMAP jpayne@68: PNG_FORMAT_ABGR_COLORMAP jpayne@68: jpayne@68: PNG_IMAGE macros jpayne@68: jpayne@68: These are convenience macros to derive information from a png_image jpayne@68: structure. The PNG_IMAGE_SAMPLE_ macros return values appropriate to the jpayne@68: actual image sample values - either the entries in the color-map or the jpayne@68: pixels in the image. The PNG_IMAGE_PIXEL_ macros return corresponding values jpayne@68: for the pixels and will always return 1 for color-mapped formats. The jpayne@68: remaining macros return information about the rows in the image and the jpayne@68: complete image. jpayne@68: jpayne@68: NOTE: All the macros that take a png_image::format parameter are compile time jpayne@68: constants if the format parameter is, itself, a constant. Therefore these jpayne@68: macros can be used in array declarations and case labels where required. jpayne@68: Similarly the macros are also pre-processor constants (sizeof is not used) so jpayne@68: they can be used in #if tests. jpayne@68: jpayne@68: PNG_IMAGE_SAMPLE_CHANNELS(fmt) jpayne@68: Returns the total number of channels in a given format: 1..4 jpayne@68: jpayne@68: PNG_IMAGE_SAMPLE_COMPONENT_SIZE(fmt) jpayne@68: Returns the size in bytes of a single component of a pixel or color-map jpayne@68: entry (as appropriate) in the image: 1 or 2. jpayne@68: jpayne@68: PNG_IMAGE_SAMPLE_SIZE(fmt) jpayne@68: This is the size of the sample data for one sample. If the image is jpayne@68: color-mapped it is the size of one color-map entry (and image pixels are jpayne@68: one byte in size), otherwise it is the size of one image pixel. jpayne@68: jpayne@68: PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(fmt) jpayne@68: The maximum size of the color-map required by the format expressed in a jpayne@68: count of components. This can be used to compile-time allocate a jpayne@68: color-map: jpayne@68: jpayne@68: png_uint_16 colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(linear_fmt)]; jpayne@68: jpayne@68: png_byte colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(sRGB_fmt)]; jpayne@68: jpayne@68: Alternatively use the PNG_IMAGE_COLORMAP_SIZE macro below to use the jpayne@68: information from one of the png_image_begin_read_ APIs and dynamically jpayne@68: allocate the required memory. jpayne@68: jpayne@68: PNG_IMAGE_COLORMAP_SIZE(fmt) jpayne@68: The size of the color-map required by the format; this is the size of the jpayne@68: color-map buffer passed to the png_image_{read,write}_colormap APIs. It is jpayne@68: a fixed number determined by the format so can easily be allocated on the jpayne@68: stack if necessary. jpayne@68: jpayne@68: Corresponding information about the pixels jpayne@68: jpayne@68: PNG_IMAGE_PIXEL_CHANNELS(fmt) jpayne@68: The number of separate channels (components) in a pixel; 1 for a jpayne@68: color-mapped image. jpayne@68: jpayne@68: PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt)\ jpayne@68: The size, in bytes, of each component in a pixel; 1 for a color-mapped jpayne@68: image. jpayne@68: jpayne@68: PNG_IMAGE_PIXEL_SIZE(fmt) jpayne@68: The size, in bytes, of a complete pixel; 1 for a color-mapped image. jpayne@68: jpayne@68: Information about the whole row, or whole image jpayne@68: jpayne@68: PNG_IMAGE_ROW_STRIDE(image) jpayne@68: Returns the total number of components in a single row of the image; this jpayne@68: is the minimum 'row stride', the minimum count of components between each jpayne@68: row. For a color-mapped image this is the minimum number of bytes in a jpayne@68: row. jpayne@68: jpayne@68: If you need the stride measured in bytes, row_stride_bytes is jpayne@68: PNG_IMAGE_ROW_STRIDE(image) * PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt) jpayne@68: plus any padding bytes that your application might need, for example jpayne@68: to start the next row on a 4-byte boundary. jpayne@68: jpayne@68: PNG_IMAGE_BUFFER_SIZE(image, row_stride) jpayne@68: Return the size, in bytes, of an image buffer given a png_image and a row jpayne@68: stride - the number of components to leave space for in each row. jpayne@68: jpayne@68: PNG_IMAGE_SIZE(image) jpayne@68: Return the size, in bytes, of the image in memory given just a png_image; jpayne@68: the row stride is the minimum stride required for the image. jpayne@68: jpayne@68: PNG_IMAGE_COLORMAP_SIZE(image) jpayne@68: Return the size, in bytes, of the color-map of this image. If the image jpayne@68: format is not a color-map format this will return a size sufficient for jpayne@68: 256 entries in the given format; check PNG_FORMAT_FLAG_COLORMAP if jpayne@68: you don't want to allocate a color-map in this case. jpayne@68: jpayne@68: PNG_IMAGE_FLAG_* jpayne@68: jpayne@68: Flags containing additional information about the image are held in jpayne@68: the 'flags' field of png_image. jpayne@68: jpayne@68: PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB == 0x01 jpayne@68: This indicates that the RGB values of the in-memory bitmap do not jpayne@68: correspond to the red, green and blue end-points defined by sRGB. jpayne@68: jpayne@68: PNG_IMAGE_FLAG_FAST == 0x02 jpayne@68: On write emphasise speed over compression; the resultant PNG file will be jpayne@68: larger but will be produced significantly faster, particular for large jpayne@68: images. Do not use this option for images which will be distributed, only jpayne@68: used it when producing intermediate files that will be read back in jpayne@68: repeatedly. For a typical 24-bit image the option will double the read jpayne@68: speed at the cost of increasing the image size by 25%, however for many jpayne@68: more compressible images the PNG file can be 10 times larger with only a jpayne@68: slight speed gain. jpayne@68: jpayne@68: PNG_IMAGE_FLAG_16BIT_sRGB == 0x04 jpayne@68: On read if the image is a 16-bit per component image and there is no gAMA jpayne@68: or sRGB chunk assume that the components are sRGB encoded. Notice that jpayne@68: images output by the simplified API always have gamma information; setting jpayne@68: this flag only affects the interpretation of 16-bit images from an jpayne@68: external source. It is recommended that the application expose this flag jpayne@68: to the user; the user can normally easily recognize the difference between jpayne@68: linear and sRGB encoding. This flag has no effect on write - the data jpayne@68: passed to the write APIs must have the correct encoding (as defined jpayne@68: above.) jpayne@68: jpayne@68: If the flag is not set (the default) input 16-bit per component data is jpayne@68: assumed to be linear. jpayne@68: jpayne@68: NOTE: the flag can only be set after the png_image_begin_read_ call, jpayne@68: because that call initializes the 'flags' field. jpayne@68: jpayne@68: READ APIs jpayne@68: jpayne@68: The png_image passed to the read APIs must have been initialized by setting jpayne@68: the png_controlp field 'opaque' to NULL (or, better, memset the whole thing.) jpayne@68: jpayne@68: int png_image_begin_read_from_file( png_imagep image, jpayne@68: const char *file_name) jpayne@68: jpayne@68: The named file is opened for read and the image header jpayne@68: is filled in from the PNG header in the file. jpayne@68: jpayne@68: int png_image_begin_read_from_stdio (png_imagep image, jpayne@68: FILE* file) jpayne@68: jpayne@68: The PNG header is read from the stdio FILE object. jpayne@68: jpayne@68: int png_image_begin_read_from_memory(png_imagep image, jpayne@68: png_const_voidp memory, size_t size) jpayne@68: jpayne@68: The PNG header is read from the given memory buffer. jpayne@68: jpayne@68: int png_image_finish_read(png_imagep image, jpayne@68: png_colorp background, void *buffer, jpayne@68: png_int_32 row_stride, void *colormap)); jpayne@68: jpayne@68: Finish reading the image into the supplied buffer and jpayne@68: clean up the png_image structure. jpayne@68: jpayne@68: row_stride is the step, in png_byte or png_uint_16 units jpayne@68: as appropriate, between adjacent rows. A positive stride jpayne@68: indicates that the top-most row is first in the buffer - jpayne@68: the normal top-down arrangement. A negative stride jpayne@68: indicates that the bottom-most row is first in the buffer. jpayne@68: jpayne@68: background need only be supplied if an alpha channel must jpayne@68: be removed from a png_byte format and the removal is to be jpayne@68: done by compositing on a solid color; otherwise it may be jpayne@68: NULL and any composition will be done directly onto the jpayne@68: buffer. The value is an sRGB color to use for the jpayne@68: background, for grayscale output the green channel is used. jpayne@68: jpayne@68: For linear output removing the alpha channel is always done jpayne@68: by compositing on black. jpayne@68: jpayne@68: void png_image_free(png_imagep image) jpayne@68: jpayne@68: Free any data allocated by libpng in image->opaque, jpayne@68: setting the pointer to NULL. May be called at any time jpayne@68: after the structure is initialized. jpayne@68: jpayne@68: When the simplified API needs to convert between sRGB and linear colorspaces, jpayne@68: the actual sRGB transfer curve defined in the sRGB specification (see the jpayne@68: article at https://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2 jpayne@68: approximation used elsewhere in libpng. jpayne@68: jpayne@68: WRITE APIS jpayne@68: jpayne@68: For write you must initialize a png_image structure to describe the image to jpayne@68: be written: jpayne@68: jpayne@68: version: must be set to PNG_IMAGE_VERSION jpayne@68: opaque: must be initialized to NULL jpayne@68: width: image width in pixels jpayne@68: height: image height in rows jpayne@68: format: the format of the data you wish to write jpayne@68: flags: set to 0 unless one of the defined flags applies; set jpayne@68: PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB for color format images jpayne@68: where the RGB values do not correspond to the colors in sRGB. jpayne@68: colormap_entries: set to the number of entries in the color-map (0 to 256) jpayne@68: jpayne@68: int png_image_write_to_file, (png_imagep image, jpayne@68: const char *file, int convert_to_8bit, const void *buffer, jpayne@68: png_int_32 row_stride, const void *colormap)); jpayne@68: jpayne@68: Write the image to the named file. jpayne@68: jpayne@68: int png_image_write_to_memory (png_imagep image, void *memory, jpayne@68: png_alloc_size_t * PNG_RESTRICT memory_bytes, jpayne@68: int convert_to_8_bit, const void *buffer, ptrdiff_t row_stride, jpayne@68: const void *colormap)); jpayne@68: jpayne@68: Write the image to memory. jpayne@68: jpayne@68: int png_image_write_to_stdio(png_imagep image, FILE *file, jpayne@68: int convert_to_8_bit, const void *buffer, jpayne@68: png_int_32 row_stride, const void *colormap) jpayne@68: jpayne@68: Write the image to the given (FILE*). jpayne@68: jpayne@68: With all write APIs if image is in one of the linear formats with jpayne@68: (png_uint_16) data then setting convert_to_8_bit will cause the output to be jpayne@68: a (png_byte) PNG gamma encoded according to the sRGB specification, otherwise jpayne@68: a 16-bit linear encoded PNG file is written. jpayne@68: jpayne@68: With all APIs row_stride is handled as in the read APIs - it is the spacing jpayne@68: from one row to the next in component sized units (float) and if negative jpayne@68: indicates a bottom-up row layout in the buffer. If you pass zero, libpng will jpayne@68: calculate the row_stride for you from the width and number of channels. jpayne@68: jpayne@68: Note that the write API does not support interlacing, sub-8-bit pixels, jpayne@68: indexed (paletted) images, or most ancillary chunks. jpayne@68: jpayne@68: .SH VI. Modifying/Customizing libpng jpayne@68: jpayne@68: There are two issues here. The first is changing how libpng does jpayne@68: standard things like memory allocation, input/output, and error handling. jpayne@68: The second deals with more complicated things like adding new chunks, jpayne@68: adding new transformations, and generally changing how libpng works. jpayne@68: Both of those are compile-time issues; that is, they are generally jpayne@68: determined at the time the code is written, and there is rarely a need jpayne@68: to provide the user with a means of changing them. jpayne@68: jpayne@68: Memory allocation, input/output, and error handling jpayne@68: jpayne@68: All of the memory allocation, input/output, and error handling in libpng jpayne@68: goes through callbacks that are user-settable. The default routines are jpayne@68: in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change jpayne@68: these functions, call the appropriate png_set_*_fn() function. jpayne@68: jpayne@68: Memory allocation is done through the functions png_malloc(), png_calloc(), jpayne@68: and png_free(). The png_malloc() and png_free() functions currently just jpayne@68: call the standard C functions and png_calloc() calls png_malloc() and then jpayne@68: clears the newly allocated memory to zero; note that png_calloc(png_ptr, size) jpayne@68: is not the same as the calloc(number, size) function provided by stdlib.h. jpayne@68: There is limited support for certain systems with segmented memory jpayne@68: architectures and the types of pointers declared by png.h match this; you jpayne@68: will have to use appropriate pointers in your application. If you prefer jpayne@68: to use a different method of allocating and freeing data, you can use jpayne@68: png_create_read_struct_2() or png_create_write_struct_2() to register your jpayne@68: own functions as described above. These functions also provide a void jpayne@68: pointer that can be retrieved via jpayne@68: jpayne@68: mem_ptr = png_get_mem_ptr(png_ptr); jpayne@68: jpayne@68: Your replacement memory functions must have prototypes as follows: jpayne@68: jpayne@68: png_voidp malloc_fn(png_structp png_ptr, jpayne@68: png_alloc_size_t size); jpayne@68: jpayne@68: void free_fn(png_structp png_ptr, png_voidp ptr); jpayne@68: jpayne@68: Your malloc_fn() must return NULL in case of failure. The png_malloc() jpayne@68: function will normally call png_error() if it receives a NULL from the jpayne@68: system memory allocator or from your replacement malloc_fn(). jpayne@68: jpayne@68: Your free_fn() will never be called with a NULL ptr, since libpng's jpayne@68: png_free() checks for NULL before calling free_fn(). jpayne@68: jpayne@68: Input/Output in libpng is done through png_read() and png_write(), jpayne@68: which currently just call fread() and fwrite(). The FILE * is stored in jpayne@68: png_struct and is initialized via png_init_io(). If you wish to change jpayne@68: the method of I/O, the library supplies callbacks that you can set jpayne@68: through the function png_set_read_fn() and png_set_write_fn() at run jpayne@68: time, instead of calling the png_init_io() function. These functions jpayne@68: also provide a void pointer that can be retrieved via the function jpayne@68: png_get_io_ptr(). For example: jpayne@68: jpayne@68: png_set_read_fn(png_structp read_ptr, jpayne@68: voidp read_io_ptr, png_rw_ptr read_data_fn) jpayne@68: jpayne@68: png_set_write_fn(png_structp write_ptr, jpayne@68: voidp write_io_ptr, png_rw_ptr write_data_fn, jpayne@68: png_flush_ptr output_flush_fn); jpayne@68: jpayne@68: voidp read_io_ptr = png_get_io_ptr(read_ptr); jpayne@68: voidp write_io_ptr = png_get_io_ptr(write_ptr); jpayne@68: jpayne@68: The replacement I/O functions must have prototypes as follows: jpayne@68: jpayne@68: void user_read_data(png_structp png_ptr, jpayne@68: png_bytep data, size_t length); jpayne@68: jpayne@68: void user_write_data(png_structp png_ptr, jpayne@68: png_bytep data, size_t length); jpayne@68: jpayne@68: void user_flush_data(png_structp png_ptr); jpayne@68: jpayne@68: The user_read_data() function is responsible for detecting and jpayne@68: handling end-of-data errors. jpayne@68: jpayne@68: Supplying NULL for the read, write, or flush functions sets them back jpayne@68: to using the default C stream functions, which expect the io_ptr to jpayne@68: point to a standard *FILE structure. It is probably a mistake jpayne@68: to use NULL for one of write_data_fn and output_flush_fn but not both jpayne@68: of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined. jpayne@68: It is an error to read from a write stream, and vice versa. jpayne@68: jpayne@68: Error handling in libpng is done through png_error() and png_warning(). jpayne@68: Errors handled through png_error() are fatal, meaning that png_error() jpayne@68: should never return to its caller. Currently, this is handled via jpayne@68: setjmp() and longjmp() (unless you have compiled libpng with jpayne@68: PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()), jpayne@68: but you could change this to do things like exit() if you should wish, jpayne@68: as long as your function does not return. jpayne@68: jpayne@68: On non-fatal errors, png_warning() is called jpayne@68: to print a warning message, and then control returns to the calling code. jpayne@68: By default png_error() and png_warning() print a message on stderr via jpayne@68: fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined jpayne@68: (because you don't want the messages) or PNG_NO_STDIO defined (because jpayne@68: fprintf() isn't available). If you wish to change the behavior of the error jpayne@68: functions, you will need to set up your own message callbacks. These jpayne@68: functions are normally supplied at the time that the png_struct is created. jpayne@68: It is also possible to redirect errors and warnings to your own replacement jpayne@68: functions after png_create_*_struct() has been called by calling: jpayne@68: jpayne@68: png_set_error_fn(png_structp png_ptr, jpayne@68: png_voidp error_ptr, png_error_ptr error_fn, jpayne@68: png_error_ptr warning_fn); jpayne@68: jpayne@68: If NULL is supplied for either error_fn or warning_fn, then the libpng jpayne@68: default function will be used, calling fprintf() and/or longjmp() if a jpayne@68: problem is encountered. The replacement error functions should have jpayne@68: parameters as follows: jpayne@68: jpayne@68: void user_error_fn(png_structp png_ptr, jpayne@68: png_const_charp error_msg); jpayne@68: jpayne@68: void user_warning_fn(png_structp png_ptr, jpayne@68: png_const_charp warning_msg); jpayne@68: jpayne@68: Then, within your user_error_fn or user_warning_fn, you can retrieve jpayne@68: the error_ptr if you need it, by calling jpayne@68: jpayne@68: png_voidp error_ptr = png_get_error_ptr(png_ptr); jpayne@68: jpayne@68: The motivation behind using setjmp() and longjmp() is the C++ throw and jpayne@68: catch exception handling methods. This makes the code much easier to write, jpayne@68: as there is no need to check every return code of every function call. jpayne@68: However, there are some uncertainties about the status of local variables jpayne@68: after a longjmp, so the user may want to be careful about doing anything jpayne@68: after setjmp returns non-zero besides returning itself. Consult your jpayne@68: compiler documentation for more details. For an alternative approach, you jpayne@68: may wish to use the "cexcept" facility (see https://cexcept.sourceforge.io/), jpayne@68: which is illustrated in pngvalid.c and in contrib/visupng. jpayne@68: jpayne@68: Beginning in libpng-1.4.0, the png_set_benign_errors() API became available. jpayne@68: You can use this to handle certain errors (normally handled as errors) jpayne@68: as warnings. jpayne@68: jpayne@68: png_set_benign_errors (png_ptr, int allowed); jpayne@68: jpayne@68: allowed: 0: treat png_benign_error() as an error. jpayne@68: 1: treat png_benign_error() as a warning. jpayne@68: jpayne@68: As of libpng-1.6.0, the default condition is to treat benign errors as jpayne@68: warnings while reading and as errors while writing. jpayne@68: jpayne@68: .SS Custom chunks jpayne@68: jpayne@68: If you need to read or write custom chunks, you may need to get deeper jpayne@68: into the libpng code. The library now has mechanisms for storing jpayne@68: and writing chunks of unknown type; you can even declare callbacks jpayne@68: for custom chunks. However, this may not be good enough if the jpayne@68: library code itself needs to know about interactions between your jpayne@68: chunk and existing `intrinsic' chunks. jpayne@68: jpayne@68: If you need to write a new intrinsic chunk, first read the PNG jpayne@68: specification. Acquire a first level of understanding of how it works. jpayne@68: Pay particular attention to the sections that describe chunk names, jpayne@68: and look at how other chunks were designed, so you can do things jpayne@68: similarly. Second, check out the sections of libpng that read and jpayne@68: write chunks. Try to find a chunk that is similar to yours and use jpayne@68: it as a template. More details can be found in the comments inside jpayne@68: the code. It is best to handle private or unknown chunks in a generic method, jpayne@68: via callback functions, instead of by modifying libpng functions. This jpayne@68: is illustrated in pngtest.c, which uses a callback function to handle a jpayne@68: private "vpAg" chunk and the new "sTER" chunk, which are both unknown to jpayne@68: libpng. jpayne@68: jpayne@68: If you wish to write your own transformation for the data, look through jpayne@68: the part of the code that does the transformations, and check out some of jpayne@68: the simpler ones to get an idea of how they work. Try to find a similar jpayne@68: transformation to the one you want to add and copy off of it. More details jpayne@68: can be found in the comments inside the code itself. jpayne@68: jpayne@68: .SS Configuring for gui/windowing platforms: jpayne@68: jpayne@68: You will need to write new error and warning functions that use the GUI jpayne@68: interface, as described previously, and set them to be the error and jpayne@68: warning functions at the time that png_create_*_struct() is called, jpayne@68: in order to have them available during the structure initialization. jpayne@68: They can be changed later via png_set_error_fn(). On some compilers, jpayne@68: you may also have to change the memory allocators (png_malloc, etc.). jpayne@68: jpayne@68: .SS Configuring zlib: jpayne@68: jpayne@68: There are special functions to configure the compression. Perhaps the jpayne@68: most useful one changes the compression level, which currently uses jpayne@68: input compression values in the range 0 - 9. The library normally jpayne@68: uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests jpayne@68: have shown that for a large majority of images, compression values in jpayne@68: the range 3-6 compress nearly as well as higher levels, and do so much jpayne@68: faster. For online applications it may be desirable to have maximum speed jpayne@68: (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also jpayne@68: specify no compression (Z_NO_COMPRESSION = 0), but this would create jpayne@68: files larger than just storing the raw bitmap. You can specify the jpayne@68: compression level by calling: jpayne@68: jpayne@68: #include zlib.h jpayne@68: png_set_compression_level(png_ptr, level); jpayne@68: jpayne@68: Another useful one is to reduce the memory level used by the library. jpayne@68: The memory level defaults to 8, but it can be lowered if you are jpayne@68: short on memory (running DOS, for example, where you only have 640K). jpayne@68: Note that the memory level does have an effect on compression; among jpayne@68: other things, lower levels will result in sections of incompressible jpayne@68: data being emitted in smaller stored blocks, with a correspondingly jpayne@68: larger relative overhead of up to 15% in the worst case. jpayne@68: jpayne@68: #include zlib.h jpayne@68: png_set_compression_mem_level(png_ptr, level); jpayne@68: jpayne@68: The other functions are for configuring zlib. They are not recommended jpayne@68: for normal use and may result in writing an invalid PNG file. See jpayne@68: zlib.h for more information on what these mean. jpayne@68: jpayne@68: #include zlib.h jpayne@68: png_set_compression_strategy(png_ptr, jpayne@68: strategy); jpayne@68: jpayne@68: png_set_compression_window_bits(png_ptr, jpayne@68: window_bits); jpayne@68: jpayne@68: png_set_compression_method(png_ptr, method); jpayne@68: jpayne@68: This controls the size of the IDAT chunks (default 8192): jpayne@68: jpayne@68: png_set_compression_buffer_size(png_ptr, size); jpayne@68: jpayne@68: As of libpng version 1.5.4, additional APIs became jpayne@68: available to set these separately for non-IDAT jpayne@68: compressed chunks such as zTXt, iTXt, and iCCP: jpayne@68: jpayne@68: #include zlib.h jpayne@68: #if PNG_LIBPNG_VER >= 10504 jpayne@68: png_set_text_compression_level(png_ptr, level); jpayne@68: jpayne@68: png_set_text_compression_mem_level(png_ptr, level); jpayne@68: jpayne@68: png_set_text_compression_strategy(png_ptr, jpayne@68: strategy); jpayne@68: jpayne@68: png_set_text_compression_window_bits(png_ptr, jpayne@68: window_bits); jpayne@68: jpayne@68: png_set_text_compression_method(png_ptr, method); jpayne@68: #endif jpayne@68: jpayne@68: .SS Controlling row filtering jpayne@68: jpayne@68: If you want to control whether libpng uses filtering or not, which jpayne@68: filters are used, and how it goes about picking row filters, you jpayne@68: can call one of these functions. The selection and configuration jpayne@68: of row filters can have a significant impact on the size and jpayne@68: encoding speed and a somewhat lesser impact on the decoding speed jpayne@68: of an image. Filtering is enabled by default for RGB and grayscale jpayne@68: images (with and without alpha), but not for paletted images nor jpayne@68: for any images with bit depths less than 8 bits/pixel. jpayne@68: jpayne@68: The 'method' parameter sets the main filtering method, which is jpayne@68: currently only '0' in the PNG 1.2 specification. The 'filters' jpayne@68: parameter sets which filter(s), if any, should be used for each jpayne@68: scanline. Possible values are PNG_ALL_FILTERS, PNG_NO_FILTERS, jpayne@68: or PNG_FAST_FILTERS to turn filtering on and off, or to turn on jpayne@68: just the fast-decoding subset of filters, respectively. jpayne@68: jpayne@68: Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB, jpayne@68: PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise jpayne@68: ORed together with '|' to specify one or more filters to use. jpayne@68: These filters are described in more detail in the PNG specification. jpayne@68: If you intend to change the filter type during the course of writing jpayne@68: the image, you should start with flags set for all of the filters jpayne@68: you intend to use so that libpng can initialize its internal jpayne@68: structures appropriately for all of the filter types. (Note that this jpayne@68: means the first row must always be adaptively filtered, because libpng jpayne@68: currently does not allocate the filter buffers until png_write_row() jpayne@68: is called for the first time.) jpayne@68: jpayne@68: filters = PNG_NO_FILTERS; jpayne@68: filters = PNG_ALL_FILTERS; jpayne@68: filters = PNG_FAST_FILTERS; jpayne@68: jpayne@68: or jpayne@68: jpayne@68: filters = PNG_FILTER_NONE | PNG_FILTER_SUB | jpayne@68: PNG_FILTER_UP | PNG_FILTER_AVG | jpayne@68: PNG_FILTER_PAETH; jpayne@68: jpayne@68: png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE, jpayne@68: filters); jpayne@68: jpayne@68: The second parameter can also be jpayne@68: PNG_INTRAPIXEL_DIFFERENCING if you are jpayne@68: writing a PNG to be embedded in a MNG jpayne@68: datastream. This parameter must be the jpayne@68: same as the value of filter_method used jpayne@68: in png_set_IHDR(). jpayne@68: jpayne@68: .SS Requesting debug printout jpayne@68: jpayne@68: The macro definition PNG_DEBUG can be used to request debugging jpayne@68: printout. Set it to an integer value in the range 0 to 3. Higher jpayne@68: numbers result in increasing amounts of debugging information. The jpayne@68: information is printed to the "stderr" file, unless another file jpayne@68: name is specified in the PNG_DEBUG_FILE macro definition. jpayne@68: jpayne@68: When PNG_DEBUG > 0, the following functions (macros) become available: jpayne@68: jpayne@68: png_debug(level, message) jpayne@68: png_debug1(level, message, p1) jpayne@68: png_debug2(level, message, p1, p2) jpayne@68: jpayne@68: in which "level" is compared to PNG_DEBUG to decide whether to print jpayne@68: the message, "message" is the formatted string to be printed, jpayne@68: and p1 and p2 are parameters that are to be embedded in the string jpayne@68: according to printf-style formatting directives. For example, jpayne@68: jpayne@68: png_debug1(2, "foo=%d", foo); jpayne@68: jpayne@68: is expanded to jpayne@68: jpayne@68: if (PNG_DEBUG > 2) jpayne@68: fprintf(PNG_DEBUG_FILE, "foo=%d\en", foo); jpayne@68: jpayne@68: When PNG_DEBUG is defined but is zero, the macros aren't defined, but you jpayne@68: can still use PNG_DEBUG to control your own debugging: jpayne@68: jpayne@68: #ifdef PNG_DEBUG jpayne@68: fprintf(stderr, ...); jpayne@68: #endif jpayne@68: jpayne@68: When PNG_DEBUG = 1, the macros are defined, but only png_debug statements jpayne@68: having level = 0 will be printed. There aren't any such statements in jpayne@68: this version of libpng, but if you insert some they will be printed. jpayne@68: jpayne@68: .SH VII. MNG support jpayne@68: jpayne@68: The MNG specification (available at http://www.libpng.org/pub/mng) allows jpayne@68: certain extensions to PNG for PNG images that are embedded in MNG datastreams. jpayne@68: Libpng can support some of these extensions. To enable them, use the jpayne@68: png_permit_mng_features() function: jpayne@68: jpayne@68: feature_set = png_permit_mng_features(png_ptr, mask) jpayne@68: jpayne@68: mask is a png_uint_32 containing the bitwise OR of the jpayne@68: features you want to enable. These include jpayne@68: PNG_FLAG_MNG_EMPTY_PLTE jpayne@68: PNG_FLAG_MNG_FILTER_64 jpayne@68: PNG_ALL_MNG_FEATURES jpayne@68: jpayne@68: feature_set is a png_uint_32 that is the bitwise AND of jpayne@68: your mask with the set of MNG features that is jpayne@68: supported by the version of libpng that you are using. jpayne@68: jpayne@68: It is an error to use this function when reading or writing a standalone jpayne@68: PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped jpayne@68: in a MNG datastream. As a minimum, it must have the MNG 8-byte signature jpayne@68: and the MHDR and MEND chunks. Libpng does not provide support for these jpayne@68: or any other MNG chunks; your application must provide its own support for jpayne@68: them. You may wish to consider using libmng (available at jpayne@68: https://www.libmng.com/) instead. jpayne@68: jpayne@68: .SH VIII. Changes to Libpng from version 0.88 jpayne@68: jpayne@68: It should be noted that versions of libpng later than 0.96 are not jpayne@68: distributed by the original libpng author, Guy Schalnat, nor by jpayne@68: Andreas Dilger, who had taken over from Guy during 1996 and 1997, and jpayne@68: distributed versions 0.89 through 0.96, but rather by another member jpayne@68: of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are jpayne@68: still alive and well, but they have moved on to other things. jpayne@68: jpayne@68: The old libpng functions png_read_init(), png_write_init(), jpayne@68: png_info_init(), png_read_destroy(), and png_write_destroy() have been jpayne@68: moved to PNG_INTERNAL in version 0.95 to discourage their use. These jpayne@68: functions will be removed from libpng version 1.4.0. jpayne@68: jpayne@68: The preferred method of creating and initializing the libpng structures is jpayne@68: via the png_create_read_struct(), png_create_write_struct(), and jpayne@68: png_create_info_struct() because they isolate the size of the structures jpayne@68: from the application, allow version error checking, and also allow the jpayne@68: use of custom error handling routines during the initialization, which jpayne@68: the old functions do not. The functions png_read_destroy() and jpayne@68: png_write_destroy() do not actually free the memory that libpng jpayne@68: allocated for these structs, but just reset the data structures, so they jpayne@68: can be used instead of png_destroy_read_struct() and jpayne@68: png_destroy_write_struct() if you feel there is too much system overhead jpayne@68: allocating and freeing the png_struct for each image read. jpayne@68: jpayne@68: Setting the error callbacks via png_set_message_fn() before jpayne@68: png_read_init() as was suggested in libpng-0.88 is no longer supported jpayne@68: because this caused applications that do not use custom error functions jpayne@68: to fail if the png_ptr was not initialized to zero. It is still possible jpayne@68: to set the error callbacks AFTER png_read_init(), or to change them with jpayne@68: png_set_error_fn(), which is essentially the same function, but with a new jpayne@68: name to force compilation errors with applications that try to use the old jpayne@68: method. jpayne@68: jpayne@68: Support for the sCAL, iCCP, iTXt, and sPLT chunks was added at libpng-1.0.6; jpayne@68: however, iTXt support was not enabled by default. jpayne@68: jpayne@68: Starting with version 1.0.7, you can find out which version of the library jpayne@68: you are using at run-time: jpayne@68: jpayne@68: png_uint_32 libpng_vn = png_access_version_number(); jpayne@68: jpayne@68: The number libpng_vn is constructed from the major version, minor jpayne@68: version with leading zero, and release number with leading zero, jpayne@68: (e.g., libpng_vn for version 1.0.7 is 10007). jpayne@68: jpayne@68: Note that this function does not take a png_ptr, so you can call it jpayne@68: before you've created one. jpayne@68: jpayne@68: You can also check which version of png.h you used when compiling your jpayne@68: application: jpayne@68: jpayne@68: png_uint_32 application_vn = PNG_LIBPNG_VER; jpayne@68: jpayne@68: .SH IX. Changes to Libpng from version 1.0.x to 1.2.x jpayne@68: jpayne@68: Support for user memory management was enabled by default. To jpayne@68: accomplish this, the functions png_create_read_struct_2(), jpayne@68: png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(), jpayne@68: png_malloc_default(), and png_free_default() were added. jpayne@68: jpayne@68: Support for the iTXt chunk has been enabled by default as of jpayne@68: version 1.2.41. jpayne@68: jpayne@68: Support for certain MNG features was enabled. jpayne@68: jpayne@68: Support for numbered error messages was added. However, we never got jpayne@68: around to actually numbering the error messages. The function jpayne@68: png_set_strip_error_numbers() was added (Note: the prototype for this jpayne@68: function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE jpayne@68: builds of libpng-1.2.15. It was restored in libpng-1.2.36). jpayne@68: jpayne@68: The png_malloc_warn() function was added at libpng-1.2.3. This issues jpayne@68: a png_warning and returns NULL instead of aborting when it fails to jpayne@68: acquire the requested memory allocation. jpayne@68: jpayne@68: Support for setting user limits on image width and height was enabled jpayne@68: by default. The functions png_set_user_limits(), png_get_user_width_max(), jpayne@68: and png_get_user_height_max() were added at libpng-1.2.6. jpayne@68: jpayne@68: The png_set_add_alpha() function was added at libpng-1.2.7. jpayne@68: jpayne@68: The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9. jpayne@68: Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the jpayne@68: tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is jpayne@68: deprecated. jpayne@68: jpayne@68: A number of macro definitions in support of runtime selection of jpayne@68: assembler code features (especially Intel MMX code support) were jpayne@68: added at libpng-1.2.0: jpayne@68: jpayne@68: PNG_ASM_FLAG_MMX_SUPPORT_COMPILED jpayne@68: PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU jpayne@68: PNG_ASM_FLAG_MMX_READ_COMBINE_ROW jpayne@68: PNG_ASM_FLAG_MMX_READ_INTERLACE jpayne@68: PNG_ASM_FLAG_MMX_READ_FILTER_SUB jpayne@68: PNG_ASM_FLAG_MMX_READ_FILTER_UP jpayne@68: PNG_ASM_FLAG_MMX_READ_FILTER_AVG jpayne@68: PNG_ASM_FLAG_MMX_READ_FILTER_PAETH jpayne@68: PNG_ASM_FLAGS_INITIALIZED jpayne@68: PNG_MMX_READ_FLAGS jpayne@68: PNG_MMX_FLAGS jpayne@68: PNG_MMX_WRITE_FLAGS jpayne@68: PNG_MMX_FLAGS jpayne@68: jpayne@68: We added the following functions in support of runtime jpayne@68: selection of assembler code features: jpayne@68: jpayne@68: png_get_mmx_flagmask() jpayne@68: png_set_mmx_thresholds() jpayne@68: png_get_asm_flags() jpayne@68: png_get_mmx_bitdepth_threshold() jpayne@68: png_get_mmx_rowbytes_threshold() jpayne@68: png_set_asm_flags() jpayne@68: jpayne@68: We replaced all of these functions with simple stubs in libpng-1.2.20, jpayne@68: when the Intel assembler code was removed due to a licensing issue. jpayne@68: jpayne@68: These macros are deprecated: jpayne@68: jpayne@68: PNG_READ_TRANSFORMS_NOT_SUPPORTED jpayne@68: PNG_PROGRESSIVE_READ_NOT_SUPPORTED jpayne@68: PNG_NO_SEQUENTIAL_READ_SUPPORTED jpayne@68: PNG_WRITE_TRANSFORMS_NOT_SUPPORTED jpayne@68: PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED jpayne@68: PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED jpayne@68: jpayne@68: They have been replaced, respectively, by: jpayne@68: jpayne@68: PNG_NO_READ_TRANSFORMS jpayne@68: PNG_NO_PROGRESSIVE_READ jpayne@68: PNG_NO_SEQUENTIAL_READ jpayne@68: PNG_NO_WRITE_TRANSFORMS jpayne@68: PNG_NO_READ_ANCILLARY_CHUNKS jpayne@68: PNG_NO_WRITE_ANCILLARY_CHUNKS jpayne@68: jpayne@68: PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been jpayne@68: deprecated since libpng-1.0.16 and libpng-1.2.6. jpayne@68: jpayne@68: The function jpayne@68: png_check_sig(sig, num) jpayne@68: was replaced with jpayne@68: png_sig_cmp(sig, 0, num) == 0 jpayne@68: It has been deprecated since libpng-0.90. jpayne@68: jpayne@68: The function jpayne@68: png_set_gray_1_2_4_to_8() jpayne@68: which also expands tRNS to alpha was replaced with jpayne@68: png_set_expand_gray_1_2_4_to_8() jpayne@68: which does not. It has been deprecated since libpng-1.0.18 and 1.2.9. jpayne@68: jpayne@68: .SH X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x jpayne@68: jpayne@68: Private libpng prototypes and macro definitions were moved from jpayne@68: png.h and pngconf.h into a new pngpriv.h header file. jpayne@68: jpayne@68: Functions png_set_benign_errors(), png_benign_error(), and jpayne@68: png_chunk_benign_error() were added. jpayne@68: jpayne@68: Support for setting the maximum amount of memory that the application jpayne@68: will allocate for reading chunks was added, as a security measure. jpayne@68: The functions png_set_chunk_cache_max() and png_get_chunk_cache_max() jpayne@68: were added to the library. jpayne@68: jpayne@68: We implemented support for I/O states by adding png_ptr member io_state jpayne@68: and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c jpayne@68: jpayne@68: We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level jpayne@68: input transforms. jpayne@68: jpayne@68: Checking for and reporting of errors in the IHDR chunk is more thorough. jpayne@68: jpayne@68: Support for global arrays was removed, to improve thread safety. jpayne@68: jpayne@68: Some obsolete/deprecated macros and functions have been removed. jpayne@68: jpayne@68: Typecasted NULL definitions such as jpayne@68: #define png_voidp_NULL (png_voidp)NULL jpayne@68: were eliminated. If you used these in your application, just use jpayne@68: NULL instead. jpayne@68: jpayne@68: The png_struct and info_struct members "trans" and "trans_values" were jpayne@68: changed to "trans_alpha" and "trans_color", respectively. jpayne@68: jpayne@68: The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles jpayne@68: were removed. jpayne@68: jpayne@68: The PNG_1_0_X and PNG_1_2_X macros were eliminated. jpayne@68: jpayne@68: The PNG_LEGACY_SUPPORTED macro was eliminated. jpayne@68: jpayne@68: Many WIN32_WCE #ifdefs were removed. jpayne@68: jpayne@68: The functions png_read_init(info_ptr), png_write_init(info_ptr), jpayne@68: png_info_init(info_ptr), png_read_destroy(), and png_write_destroy() jpayne@68: have been removed. They have been deprecated since libpng-0.95. jpayne@68: jpayne@68: The png_permit_empty_plte() was removed. It has been deprecated jpayne@68: since libpng-1.0.9. Use png_permit_mng_features() instead. jpayne@68: jpayne@68: We removed the obsolete stub functions png_get_mmx_flagmask(), jpayne@68: png_set_mmx_thresholds(), png_get_asm_flags(), jpayne@68: png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(), jpayne@68: png_set_asm_flags(), and png_mmx_supported() jpayne@68: jpayne@68: We removed the obsolete png_check_sig(), png_memcpy_check(), and jpayne@68: png_memset_check() functions. Instead use png_sig_cmp() == 0, jpayne@68: memcpy(), and memset(), respectively. jpayne@68: jpayne@68: The function png_set_gray_1_2_4_to_8() was removed. It has been jpayne@68: deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with jpayne@68: png_set_expand_gray_1_2_4_to_8() because the former function also jpayne@68: expanded any tRNS chunk to an alpha channel. jpayne@68: jpayne@68: Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32 jpayne@68: were added and are used by default instead of the corresponding jpayne@68: functions. Unfortunately, jpayne@68: from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the jpayne@68: function) incorrectly returned a value of type png_uint_32. jpayne@68: jpayne@68: We changed the prototype for png_malloc() from jpayne@68: png_malloc(png_structp png_ptr, png_uint_32 size) jpayne@68: to jpayne@68: png_malloc(png_structp png_ptr, png_alloc_size_t size) jpayne@68: jpayne@68: This also applies to the prototype for the user replacement malloc_fn(). jpayne@68: jpayne@68: The png_calloc() function was added and is used in place of jpayne@68: of "png_malloc(); memset();" except in the case in png_read_png() jpayne@68: where the array consists of pointers; in this case a "for" loop is used jpayne@68: after the png_malloc() to set the pointers to NULL, to give robust. jpayne@68: behavior in case the application runs out of memory part-way through jpayne@68: the process. jpayne@68: jpayne@68: We changed the prototypes of png_get_compression_buffer_size() and jpayne@68: png_set_compression_buffer_size() to work with size_t instead of jpayne@68: png_uint_32. jpayne@68: jpayne@68: Support for numbered error messages was removed by default, since we jpayne@68: never got around to actually numbering the error messages. The function jpayne@68: png_set_strip_error_numbers() was removed from the library by default. jpayne@68: jpayne@68: The png_zalloc() and png_zfree() functions are no longer exported. jpayne@68: The png_zalloc() function no longer zeroes out the memory that it jpayne@68: allocates. Applications that called png_zalloc(png_ptr, number, size) jpayne@68: can call png_calloc(png_ptr, number*size) instead, and can call jpayne@68: png_free() instead of png_zfree(). jpayne@68: jpayne@68: Support for dithering was disabled by default in libpng-1.4.0, because jpayne@68: it has not been well tested and doesn't actually "dither". jpayne@68: The code was not jpayne@68: removed, however, and could be enabled by building libpng with jpayne@68: PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support jpayne@68: was re-enabled, but the function was renamed png_set_quantize() to jpayne@68: reflect more accurately what it actually does. At the same time, jpayne@68: the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to jpayne@68: PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED jpayne@68: was renamed to PNG_READ_QUANTIZE_SUPPORTED. jpayne@68: jpayne@68: We removed the trailing '.' from the warning and error messages. jpayne@68: jpayne@68: .SH XI. Changes to Libpng from version 1.4.x to 1.5.x jpayne@68: jpayne@68: From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the jpayne@68: function) incorrectly returned a value of type png_uint_32. jpayne@68: The incorrect macro was removed from libpng-1.4.5. jpayne@68: jpayne@68: Checking for invalid palette index on write was added at libpng jpayne@68: 1.5.10. If a pixel contains an invalid (out-of-range) index libpng issues jpayne@68: a benign error. This is enabled by default because this condition is an jpayne@68: error according to the PNG specification, Clause 11.3.2, but the error can jpayne@68: be ignored in each png_ptr with jpayne@68: jpayne@68: png_set_check_for_invalid_index(png_ptr, allowed); jpayne@68: jpayne@68: allowed - one of jpayne@68: 0: disable benign error (accept the jpayne@68: invalid data without warning). jpayne@68: 1: enable benign error (treat the jpayne@68: invalid data as an error or a jpayne@68: warning). jpayne@68: jpayne@68: If the error is ignored, or if png_benign_error() treats it as a warning, jpayne@68: any invalid pixels are decoded as opaque black by the decoder and written jpayne@68: as-is by the encoder. jpayne@68: jpayne@68: Retrieving the maximum palette index found was added at libpng-1.5.15. jpayne@68: This statement must appear after png_read_png() or png_read_image() while jpayne@68: reading, and after png_write_png() or png_write_image() while writing. jpayne@68: jpayne@68: int max_palette = png_get_palette_max(png_ptr, info_ptr); jpayne@68: jpayne@68: This will return the maximum palette index found in the image, or "\-1" if jpayne@68: the palette was not checked, or "0" if no palette was found. Note that this jpayne@68: does not account for any palette index used by ancillary chunks such as the jpayne@68: bKGD chunk; you must check those separately to determine the maximum jpayne@68: palette index actually used. jpayne@68: jpayne@68: There are no substantial API changes between the non-deprecated parts of jpayne@68: the 1.4.5 API and the 1.5.0 API; however, the ability to directly access jpayne@68: members of the main libpng control structures, png_struct and png_info, jpayne@68: deprecated in earlier versions of libpng, has been completely removed from jpayne@68: libpng 1.5, and new private "pngstruct.h", "pnginfo.h", and "pngdebug.h" jpayne@68: header files were created. jpayne@68: jpayne@68: We no longer include zlib.h in png.h. The include statement has been moved jpayne@68: to pngstruct.h, where it is not accessible by applications. Applications that jpayne@68: need access to information in zlib.h will need to add the '#include "zlib.h"' jpayne@68: directive. It does not matter whether this is placed prior to or after jpayne@68: the '"#include png.h"' directive. jpayne@68: jpayne@68: The png_sprintf(), png_strcpy(), and png_strncpy() macros are no longer used jpayne@68: and were removed. jpayne@68: jpayne@68: We moved the png_strlen(), png_memcpy(), png_memset(), and png_memcmp() jpayne@68: macros into a private header file (pngpriv.h) that is not accessible to jpayne@68: applications. jpayne@68: jpayne@68: In png_get_iCCP, the type of "profile" was changed from png_charpp jpayne@68: to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep. jpayne@68: jpayne@68: There are changes of form in png.h, including new and changed macros to jpayne@68: declare parts of the API. Some API functions with arguments that are jpayne@68: pointers to data not modified within the function have been corrected to jpayne@68: declare these arguments with const. jpayne@68: jpayne@68: Much of the internal use of C macros to control the library build has also jpayne@68: changed and some of this is visible in the exported header files, in jpayne@68: particular the use of macros to control data and API elements visible jpayne@68: during application compilation may require significant revision to jpayne@68: application code. (It is extremely rare for an application to do this.) jpayne@68: jpayne@68: Any program that compiled against libpng 1.4 and did not use deprecated jpayne@68: features or access internal library structures should compile and work jpayne@68: against libpng 1.5, except for the change in the prototype for jpayne@68: png_get_iCCP() and png_set_iCCP() API functions mentioned above. jpayne@68: jpayne@68: libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of jpayne@68: interlaced images. The macros return the number of rows and columns in jpayne@68: each pass and information that can be used to de-interlace and (if jpayne@68: absolutely necessary) interlace an image. jpayne@68: jpayne@68: libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls jpayne@68: the application-provided png_longjmp_ptr on the internal, but application jpayne@68: initialized, longjmp buffer. It is provided as a convenience to avoid jpayne@68: the need to use the png_jmpbuf macro, which had the unnecessary side jpayne@68: effect of resetting the internal png_longjmp_ptr value. jpayne@68: jpayne@68: libpng 1.5.0 includes a complete fixed point API. By default this is jpayne@68: present along with the corresponding floating point API. In general the jpayne@68: fixed point API is faster and smaller than the floating point one because jpayne@68: the PNG file format used fixed point, not floating point. This applies jpayne@68: even if the library uses floating point in internal calculations. A new jpayne@68: macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library jpayne@68: uses floating point arithmetic (the default) or fixed point arithmetic jpayne@68: internally for performance critical calculations such as gamma correction. jpayne@68: In some cases, the gamma calculations may produce slightly different jpayne@68: results. This has changed the results in png_rgb_to_gray and in alpha jpayne@68: composition (png_set_background for example). This applies even if the jpayne@68: original image was already linear (gamma == 1.0) and, therefore, it is jpayne@68: not necessary to linearize the image. This is because libpng has *not* jpayne@68: been changed to optimize that case correctly, yet. jpayne@68: jpayne@68: Fixed point support for the sCAL chunk comes with an important caveat; jpayne@68: the sCAL specification uses a decimal encoding of floating point values jpayne@68: and the accuracy of PNG fixed point values is insufficient for jpayne@68: representation of these values. Consequently a "string" API jpayne@68: (png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading jpayne@68: arbitrary sCAL chunks in the absence of either the floating point API or jpayne@68: internal floating point calculations. Starting with libpng-1.5.0, both jpayne@68: of these functions are present when PNG_sCAL_SUPPORTED is defined. Prior jpayne@68: to libpng-1.5.0, their presence also depended upon PNG_FIXED_POINT_SUPPORTED jpayne@68: being defined and PNG_FLOATING_POINT_SUPPORTED not being defined. jpayne@68: jpayne@68: Applications no longer need to include the optional distribution header jpayne@68: file pngusr.h or define the corresponding macros during application jpayne@68: build in order to see the correct variant of the libpng API. From 1.5.0 jpayne@68: application code can check for the corresponding _SUPPORTED macro: jpayne@68: jpayne@68: #ifdef PNG_INCH_CONVERSIONS_SUPPORTED jpayne@68: /* code that uses the inch conversion APIs. */ jpayne@68: #endif jpayne@68: jpayne@68: This macro will only be defined if the inch conversion functions have been jpayne@68: compiled into libpng. The full set of macros, and whether or not support jpayne@68: has been compiled in, are available in the header file pnglibconf.h. jpayne@68: This header file is specific to the libpng build. Notice that prior to jpayne@68: 1.5.0 the _SUPPORTED macros would always have the default definition unless jpayne@68: reset by pngusr.h or by explicit settings on the compiler command line. jpayne@68: These settings may produce compiler warnings or errors in 1.5.0 because jpayne@68: of macro redefinition. jpayne@68: jpayne@68: Applications can now choose whether to use these macros or to call the jpayne@68: corresponding function by defining PNG_USE_READ_MACROS or jpayne@68: PNG_NO_USE_READ_MACROS before including png.h. Notice that this is jpayne@68: only supported from 1.5.0; defining PNG_NO_USE_READ_MACROS prior to 1.5.0 jpayne@68: will lead to a link failure. jpayne@68: jpayne@68: Prior to libpng-1.5.4, the zlib compressor used the same set of parameters jpayne@68: when compressing the IDAT data and textual data such as zTXt and iCCP. jpayne@68: In libpng-1.5.4 we reinitialized the zlib stream for each type of data. jpayne@68: We added five png_set_text_*() functions for setting the parameters to jpayne@68: use with textual data. jpayne@68: jpayne@68: Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED jpayne@68: option was off by default, and slightly inaccurate scaling occurred. jpayne@68: This option can no longer be turned off, and the choice of accurate jpayne@68: or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8() jpayne@68: API for accurate scaling or the old png_set_strip_16_to_8() API for simple jpayne@68: chopping. In libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED jpayne@68: macro became PNG_READ_SCALE_16_TO_8_SUPPORTED, and the PNG_READ_16_TO_8 jpayne@68: macro became PNG_READ_STRIP_16_TO_8_SUPPORTED, to enable the two jpayne@68: png_set_*_16_to_8() functions separately. jpayne@68: jpayne@68: Prior to libpng-1.5.4, the png_set_user_limits() function could only be jpayne@68: used to reduce the width and height limits from the value of jpayne@68: PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said jpayne@68: that it could be used to override them. Now this function will reduce or jpayne@68: increase the limits. jpayne@68: jpayne@68: Starting in libpng-1.5.22, default user limits were established. These jpayne@68: can be overridden by application calls to png_set_user_limits(), jpayne@68: png_set_user_chunk_cache_max(), and/or png_set_user_malloc_max(). jpayne@68: The limits are now jpayne@68: max possible default jpayne@68: png_user_width_max 0x7fffffff 1,000,000 jpayne@68: png_user_height_max 0x7fffffff 1,000,000 jpayne@68: png_user_chunk_cache_max 0 (unlimited) 1000 jpayne@68: png_user_chunk_malloc_max 0 (unlimited) 8,000,000 jpayne@68: jpayne@68: The png_set_option() function (and the "options" member of the png struct) was jpayne@68: added to libpng-1.5.15, with option PNG_ARM_NEON. jpayne@68: jpayne@68: The library now supports a complete fixed point implementation and can jpayne@68: thus be used on systems that have no floating point support or very jpayne@68: limited or slow support. Previously gamma correction, an essential part jpayne@68: of complete PNG support, required reasonably fast floating point. jpayne@68: jpayne@68: As part of this the choice of internal implementation has been made jpayne@68: independent of the choice of fixed versus floating point APIs and all the jpayne@68: missing fixed point APIs have been implemented. jpayne@68: jpayne@68: The exact mechanism used to control attributes of API functions has jpayne@68: changed, as described in the INSTALL file. jpayne@68: jpayne@68: A new test program, pngvalid, is provided in addition to pngtest. jpayne@68: pngvalid validates the arithmetic accuracy of the gamma correction jpayne@68: calculations and includes a number of validations of the file format. jpayne@68: A subset of the full range of tests is run when "make check" is done jpayne@68: (in the 'configure' build.) pngvalid also allows total allocated memory jpayne@68: usage to be evaluated and performs additional memory overwrite validation. jpayne@68: jpayne@68: Many changes to individual feature macros have been made. The following jpayne@68: are the changes most likely to be noticed by library builders who jpayne@68: configure libpng: jpayne@68: jpayne@68: 1) All feature macros now have consistent naming: jpayne@68: jpayne@68: #define PNG_NO_feature turns the feature off jpayne@68: #define PNG_feature_SUPPORTED turns the feature on jpayne@68: jpayne@68: pnglibconf.h contains one line for each feature macro which is either: jpayne@68: jpayne@68: #define PNG_feature_SUPPORTED jpayne@68: jpayne@68: if the feature is supported or: jpayne@68: jpayne@68: /*#undef PNG_feature_SUPPORTED*/ jpayne@68: jpayne@68: if it is not. Library code consistently checks for the 'SUPPORTED' macro. jpayne@68: It does not, and libpng applications should not, check for the 'NO' macro jpayne@68: which will not normally be defined even if the feature is not supported. jpayne@68: The 'NO' macros are only used internally for setting or not setting the jpayne@68: corresponding 'SUPPORTED' macros. jpayne@68: jpayne@68: Compatibility with the old names is provided as follows: jpayne@68: jpayne@68: PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED jpayne@68: jpayne@68: And the following definitions disable the corresponding feature: jpayne@68: jpayne@68: PNG_SETJMP_NOT_SUPPORTED disables SETJMP jpayne@68: PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS jpayne@68: PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV jpayne@68: PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS jpayne@68: PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS jpayne@68: PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS jpayne@68: jpayne@68: Library builders should remove use of the above, inconsistent, names. jpayne@68: jpayne@68: 2) Warning and error message formatting was previously conditional on jpayne@68: the STDIO feature. The library has been changed to use the jpayne@68: CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled jpayne@68: the library no longer uses the printf(3) functions, even though the jpayne@68: default read/write implementations use (FILE) style stdio.h functions. jpayne@68: jpayne@68: 3) Three feature macros now control the fixed/floating point decisions: jpayne@68: jpayne@68: PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs jpayne@68: jpayne@68: PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in jpayne@68: practice these are normally required internally anyway (because the PNG jpayne@68: file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT jpayne@68: merely stops the function from being exported. jpayne@68: jpayne@68: PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating jpayne@68: point implementation or the fixed point one. Typically the fixed point jpayne@68: implementation is larger and slower than the floating point implementation jpayne@68: on a system that supports floating point; however, it may be faster on a jpayne@68: system which lacks floating point hardware and therefore uses a software jpayne@68: emulation. jpayne@68: jpayne@68: 4) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the jpayne@68: functions to read and write ints to be disabled independently of jpayne@68: PNG_USE_READ_MACROS, which allows libpng to be built with the functions jpayne@68: even though the default is to use the macros - this allows applications jpayne@68: to choose at app buildtime whether or not to use macros (previously jpayne@68: impossible because the functions weren't in the default build.) jpayne@68: jpayne@68: .SH XII. Changes to Libpng from version 1.5.x to 1.6.x jpayne@68: jpayne@68: A "simplified API" has been added (see documentation in png.h and a simple jpayne@68: example in contrib/examples/pngtopng.c). The new publicly visible API jpayne@68: includes the following: jpayne@68: jpayne@68: macros: jpayne@68: PNG_FORMAT_* jpayne@68: PNG_IMAGE_* jpayne@68: structures: jpayne@68: png_control jpayne@68: png_image jpayne@68: read functions jpayne@68: png_image_begin_read_from_file() jpayne@68: png_image_begin_read_from_stdio() jpayne@68: png_image_begin_read_from_memory() jpayne@68: png_image_finish_read() jpayne@68: png_image_free() jpayne@68: write functions jpayne@68: png_image_write_to_file() jpayne@68: png_image_write_to_memory() jpayne@68: png_image_write_to_stdio() jpayne@68: jpayne@68: Starting with libpng-1.6.0, you can configure libpng to prefix all exported jpayne@68: symbols, using the PNG_PREFIX macro. jpayne@68: jpayne@68: We no longer include string.h in png.h. The include statement has been moved jpayne@68: to pngpriv.h, where it is not accessible by applications. Applications that jpayne@68: need access to information in string.h must add an '#include ' jpayne@68: directive. It does not matter whether this is placed prior to or after jpayne@68: the '#include "png.h"' directive. jpayne@68: jpayne@68: The following API are now DEPRECATED: jpayne@68: png_info_init_3() jpayne@68: png_convert_to_rfc1123() which has been replaced jpayne@68: with png_convert_to_rfc1123_buffer() jpayne@68: png_malloc_default() jpayne@68: png_free_default() jpayne@68: png_reset_zstream() jpayne@68: jpayne@68: The following have been removed: jpayne@68: png_get_io_chunk_name(), which has been replaced jpayne@68: with png_get_io_chunk_type(). The new jpayne@68: function returns a 32-bit integer instead of jpayne@68: a string. jpayne@68: The png_sizeof(), png_strlen(), png_memcpy(), png_memcmp(), and jpayne@68: png_memset() macros are no longer used in the libpng sources and jpayne@68: have been removed. These had already been made invisible to applications jpayne@68: (i.e., defined in the private pngpriv.h header file) since libpng-1.5.0. jpayne@68: jpayne@68: The signatures of many exported functions were changed, such that jpayne@68: png_structp became png_structrp or png_const_structrp jpayne@68: png_infop became png_inforp or png_const_inforp jpayne@68: where "rp" indicates a "restricted pointer". jpayne@68: jpayne@68: Dropped support for 16-bit platforms. The support for FAR/far types has jpayne@68: been eliminated and the definition of png_alloc_size_t is now controlled jpayne@68: by a flag so that 'small size_t' systems can select it if necessary. jpayne@68: jpayne@68: Error detection in some chunks has improved; in particular the iCCP chunk jpayne@68: reader now does pretty complete validation of the basic format. Some bad jpayne@68: profiles that were previously accepted are now accepted with a warning or jpayne@68: rejected, depending upon the png_set_benign_errors() setting, in particular jpayne@68: the very old broken Microsoft/HP 3144-byte sRGB profile. Starting with jpayne@68: libpng-1.6.11, recognizing and checking sRGB profiles can be avoided by jpayne@68: means of jpayne@68: jpayne@68: #if defined(PNG_SKIP_sRGB_CHECK_PROFILE) && \ jpayne@68: defined(PNG_SET_OPTION_SUPPORTED) jpayne@68: png_set_option(png_ptr, PNG_SKIP_sRGB_CHECK_PROFILE, jpayne@68: PNG_OPTION_ON); jpayne@68: #endif jpayne@68: jpayne@68: It's not a good idea to do this if you are using the "simplified API", jpayne@68: which needs to be able to recognize sRGB profiles conveyed via the iCCP jpayne@68: chunk. jpayne@68: jpayne@68: The PNG spec requirement that only grayscale profiles may appear in images jpayne@68: with color type 0 or 4 and that even if the image only contains gray pixels, jpayne@68: only RGB profiles may appear in images with color type 2, 3, or 6, is now jpayne@68: enforced. The sRGB chunk is allowed to appear in images with any color type jpayne@68: and is interpreted by libpng to convey a one-tracer-curve gray profile or a jpayne@68: three-tracer-curve RGB profile as appropriate. jpayne@68: jpayne@68: Libpng 1.5.x erroneously used /MD for Debug DLL builds; if you used the debug jpayne@68: builds in your app and you changed your app to use /MD you will need to jpayne@68: change it back to /MDd for libpng 1.6.x. jpayne@68: jpayne@68: Prior to libpng-1.6.0 a warning would be issued if the iTXt chunk contained jpayne@68: an empty language field or an empty translated keyword. Both of these jpayne@68: are allowed by the PNG specification, so these warnings are no longer issued. jpayne@68: jpayne@68: The library now issues an error if the application attempts to set a jpayne@68: transform after it calls png_read_update_info() or if it attempts to call jpayne@68: both png_read_update_info() and png_start_read_image() or to call either jpayne@68: of them more than once. jpayne@68: jpayne@68: The default condition for benign_errors is now to treat benign errors as jpayne@68: warnings while reading and as errors while writing. jpayne@68: jpayne@68: The library now issues a warning if both background processing and RGB to jpayne@68: gray are used when gamma correction happens. As with previous versions of jpayne@68: the library the results are numerically very incorrect in this case. jpayne@68: jpayne@68: There are some minor arithmetic changes in some transforms such as jpayne@68: png_set_background(), that might be detected by certain regression tests. jpayne@68: jpayne@68: Unknown chunk handling has been improved internally, without any API change. jpayne@68: This adds more correct option control of the unknown handling, corrects jpayne@68: a pre-existing bug where the per-chunk 'keep' setting is ignored, and makes jpayne@68: it possible to skip IDAT chunks in the sequential reader. jpayne@68: jpayne@68: The machine-generated configure files are no longer included in branches jpayne@68: libpng16 and later of the GIT repository. They continue to be included jpayne@68: in the tarball releases, however. jpayne@68: jpayne@68: Libpng-1.6.0 through 1.6.2 used the CMF bytes at the beginning of the IDAT jpayne@68: stream to set the size of the sliding window for reading instead of using the jpayne@68: default 32-kbyte sliding window size. It was discovered that there are jpayne@68: hundreds of PNG files in the wild that have incorrect CMF bytes that caused jpayne@68: zlib to issue the "invalid distance too far back" error and reject the file. jpayne@68: Libpng-1.6.3 and later calculate their own safe CMF from the image dimensions, jpayne@68: provide a way to revert to the libpng-1.5.x behavior (ignoring the CMF bytes jpayne@68: and using a 32-kbyte sliding window), by using jpayne@68: jpayne@68: png_set_option(png_ptr, PNG_MAXIMUM_INFLATE_WINDOW, jpayne@68: PNG_OPTION_ON); jpayne@68: jpayne@68: and provide a tool (contrib/tools/pngfix) for rewriting a PNG file while jpayne@68: optimizing the CMF bytes in its IDAT chunk correctly. jpayne@68: jpayne@68: Libpng-1.6.0 and libpng-1.6.1 wrote uncompressed iTXt chunks with the wrong jpayne@68: length, which resulted in PNG files that cannot be read beyond the bad iTXt jpayne@68: chunk. This error was fixed in libpng-1.6.3, and a tool (called jpayne@68: contrib/tools/png-fix-itxt) has been added to the libpng distribution. jpayne@68: jpayne@68: Starting with libpng-1.6.17, the PNG_SAFE_LIMITS macro was eliminated jpayne@68: and safe limits are used by default (users who need larger limits jpayne@68: can still override them at compile time or run time, as described above). jpayne@68: jpayne@68: The new limits are jpayne@68: default spec limit jpayne@68: png_user_width_max 1,000,000 2,147,483,647 jpayne@68: png_user_height_max 1,000,000 2,147,483,647 jpayne@68: png_user_chunk_cache_max 128 unlimited jpayne@68: png_user_chunk_malloc_max 8,000,000 unlimited jpayne@68: jpayne@68: Starting with libpng-1.6.18, a PNG_RELEASE_BUILD macro was added, which allows jpayne@68: library builders to control compilation for an installed system (a release build). jpayne@68: It can be set for testing debug or beta builds to ensure that they will compile jpayne@68: when the build type is switched to RC or STABLE. In essence this overrides the jpayne@68: PNG_LIBPNG_BUILD_BASE_TYPE definition which is not directly user controllable. jpayne@68: jpayne@68: Starting with libpng-1.6.19, attempting to set an over-length PLTE chunk jpayne@68: is an error. Previously this requirement of the PNG specification was not jpayne@68: enforced, and the palette was always limited to 256 entries. An over-length jpayne@68: PLTE chunk found in an input PNG is silently truncated. jpayne@68: jpayne@68: Starting with libpng-1.6.31, the eXIf chunk is supported. Libpng does not jpayne@68: attempt to decode the Exif profile; it simply returns a byte array jpayne@68: containing the profile to the calling application which must do its own jpayne@68: decoding. jpayne@68: jpayne@68: .SH XIII. Detecting libpng jpayne@68: jpayne@68: The png_get_io_ptr() function has been present since libpng-0.88, has never jpayne@68: changed, and is unaffected by conditional compilation macros. It is the jpayne@68: best choice for use in configure scripts for detecting the presence of any jpayne@68: libpng version since 0.88. In an autoconf "configure.in" you could use jpayne@68: jpayne@68: AC_CHECK_LIB(png, png_get_io_ptr, ...) jpayne@68: jpayne@68: .SH XV. Source code repository jpayne@68: jpayne@68: Since about February 2009, version 1.2.34, libpng has been under "git" source jpayne@68: control. The git repository was built from old libpng-x.y.z.tar.gz files jpayne@68: going back to version 0.70. You can access the git repository (read only) jpayne@68: at jpayne@68: jpayne@68: https://github.com/pnggroup/libpng or jpayne@68: https://git.code.sf.net/p/libpng/code.git jpayne@68: jpayne@68: or you can browse it with a web browser at jpayne@68: jpayne@68: https://github.com/pnggroup/libpng or jpayne@68: https://sourceforge.net/p/libpng/code/ci/libpng16/tree/ jpayne@68: jpayne@68: Patches can be sent to png-mng-implement at lists.sourceforge.net or jpayne@68: uploaded to the libpng bug tracker at jpayne@68: jpayne@68: https://libpng.sourceforge.io/ jpayne@68: jpayne@68: or as a "pull request" to jpayne@68: jpayne@68: https://github.com/pnggroup/libpng/pulls jpayne@68: jpayne@68: We also accept patches built from the tar or zip distributions, and jpayne@68: simple verbal descriptions of bug fixes, reported either to the jpayne@68: SourceForge bug tracker, to the png-mng-implement at lists.sf.net jpayne@68: mailing list, as github issues. jpayne@68: jpayne@68: .SH XV. Coding style jpayne@68: jpayne@68: Our coding style is similar to the "Allman" style jpayne@68: (See https://en.wikipedia.org/wiki/Indent_style#Allman_style), with curly jpayne@68: braces on separate lines: jpayne@68: jpayne@68: if (condition) jpayne@68: { jpayne@68: action; jpayne@68: } jpayne@68: jpayne@68: else if (another condition) jpayne@68: { jpayne@68: another action; jpayne@68: } jpayne@68: jpayne@68: The braces can be omitted from simple one-line actions: jpayne@68: jpayne@68: if (condition) jpayne@68: return 0; jpayne@68: jpayne@68: We use 3-space indentation, except for continued statements which jpayne@68: are usually indented the same as the first line of the statement jpayne@68: plus four more spaces. jpayne@68: jpayne@68: For macro definitions we use 2-space indentation, always leaving the "#" jpayne@68: in the first column. jpayne@68: jpayne@68: #ifndef PNG_NO_FEATURE jpayne@68: # ifndef PNG_FEATURE_SUPPORTED jpayne@68: # define PNG_FEATURE_SUPPORTED jpayne@68: # endif jpayne@68: #endif jpayne@68: jpayne@68: Comments appear with the leading "/*" at the same indentation as jpayne@68: the statement that follows the comment: jpayne@68: jpayne@68: /* Single-line comment */ jpayne@68: statement; jpayne@68: jpayne@68: /* This is a multiple-line jpayne@68: * comment. jpayne@68: */ jpayne@68: statement; jpayne@68: jpayne@68: Very short comments can be placed after the end of the statement jpayne@68: to which they pertain: jpayne@68: jpayne@68: statement; /* comment */ jpayne@68: jpayne@68: We don't use C++ style ("//") comments. We have, however, jpayne@68: used them in the past in some now-abandoned MMX assembler jpayne@68: code. jpayne@68: jpayne@68: Functions and their curly braces are not indented, and jpayne@68: exported functions are marked with PNGAPI: jpayne@68: jpayne@68: /* This is a public function that is visible to jpayne@68: * application programmers. It does thus-and-so. jpayne@68: */ jpayne@68: void PNGAPI jpayne@68: png_exported_function(png_ptr, png_info, foo) jpayne@68: { jpayne@68: body; jpayne@68: } jpayne@68: jpayne@68: The return type and decorations are placed on a separate line jpayne@68: ahead of the function name, as illustrated above. jpayne@68: jpayne@68: The prototypes for all exported functions appear in png.h, jpayne@68: above the comment that says jpayne@68: jpayne@68: /* Maintainer: Put new public prototypes here ... */ jpayne@68: jpayne@68: We mark all non-exported functions with "/* PRIVATE */"": jpayne@68: jpayne@68: void /* PRIVATE */ jpayne@68: png_non_exported_function(png_ptr, png_info, foo) jpayne@68: { jpayne@68: body; jpayne@68: } jpayne@68: jpayne@68: The prototypes for non-exported functions (except for those in jpayne@68: pngtest) appear in pngpriv.h above the comment that says jpayne@68: jpayne@68: /* Maintainer: Put new private prototypes here ^ */ jpayne@68: jpayne@68: To avoid polluting the global namespace, the names of all exported jpayne@68: functions and variables begin with "png_", and all publicly visible C jpayne@68: preprocessor macros begin with "PNG". We request that applications that jpayne@68: use libpng *not* begin any of their own symbols with either of these strings. jpayne@68: jpayne@68: We put a space after the "sizeof" operator and we omit the jpayne@68: optional parentheses around its argument when the argument jpayne@68: is an expression, not a type name, and we always enclose the jpayne@68: sizeof operator, with its argument, in parentheses: jpayne@68: jpayne@68: (sizeof (png_uint_32)) jpayne@68: (sizeof array) jpayne@68: jpayne@68: Prior to libpng-1.6.0 we used a "png_sizeof()" macro, formatted as jpayne@68: though it were a function. jpayne@68: jpayne@68: Control keywords if, for, while, and switch are always followed by a space jpayne@68: to distinguish them from function calls, which have no trailing space. jpayne@68: jpayne@68: We put a space after each comma and after each semicolon jpayne@68: in "for" statements, and we put spaces before and after each jpayne@68: C binary operator and after "for" or "while", and before jpayne@68: "?". We don't put a space between a typecast and the expression jpayne@68: being cast, nor do we put one between a function name and the jpayne@68: left parenthesis that follows it: jpayne@68: jpayne@68: for (i = 2; i > 0; \-\-i) jpayne@68: y[i] = a(x) + (int)b; jpayne@68: jpayne@68: We prefer #ifdef and #ifndef to #if defined() and #if !defined() jpayne@68: when there is only one macro being tested. We always use parentheses jpayne@68: with "defined". jpayne@68: jpayne@68: We express integer constants that are used as bit masks in hex format, jpayne@68: with an even number of lower-case hex digits, and to make them unsigned jpayne@68: (e.g., 0x00U, 0xffU, 0x0100U) and long if they are greater than 0x7fff jpayne@68: (e.g., 0xffffUL). jpayne@68: jpayne@68: We prefer to use underscores rather than camelCase in names, except jpayne@68: for a few type names that we inherit from zlib.h. jpayne@68: jpayne@68: We prefer "if (something != 0)" and "if (something == 0)" over jpayne@68: "if (something)" and if "(!something)", respectively, and for pointers jpayne@68: we prefer "if (some_pointer != NULL)" or "if (some_pointer == NULL)". jpayne@68: jpayne@68: We do not use the TAB character for indentation in the C sources. jpayne@68: jpayne@68: Lines do not exceed 80 characters. jpayne@68: jpayne@68: Other rules can be inferred by inspecting the libpng source. jpayne@68: jpayne@68: .SH NOTE jpayne@68: jpayne@68: Note about libpng version numbers: jpayne@68: jpayne@68: Due to various miscommunications, unforeseen code incompatibilities jpayne@68: and occasional factors outside the authors' control, version numbering jpayne@68: on the library has not always been consistent and straightforward. jpayne@68: The following table summarizes matters since version 0.89c, which was jpayne@68: the first widely used release: jpayne@68: jpayne@68: source png.h png.h shared-lib jpayne@68: version string int version jpayne@68: ------- ------ ----- ---------- jpayne@68: 0.89c "1.0 beta 3" 0.89 89 1.0.89 jpayne@68: 0.90 "1.0 beta 4" 0.90 90 0.90 [should have been 2.0.90] jpayne@68: 0.95 "1.0 beta 5" 0.95 95 0.95 [should have been 2.0.95] jpayne@68: 0.96 "1.0 beta 6" 0.96 96 0.96 [should have been 2.0.96] jpayne@68: 0.97b "1.00.97 beta 7" 1.00.97 97 1.0.1 [should have been 2.0.97] jpayne@68: 0.97c 0.97 97 2.0.97 jpayne@68: 0.98 0.98 98 2.0.98 jpayne@68: 0.99 0.99 98 2.0.99 jpayne@68: 0.99a-m 0.99 99 2.0.99 jpayne@68: 1.00 1.00 100 2.1.0 [100 should be 10000] jpayne@68: 1.0.0 (from here on, the 100 2.1.0 [100 should be 10000] jpayne@68: 1.0.1 png.h string is 10001 2.1.0 jpayne@68: 1.0.1a-e identical to the 10002 from here on, the shared library jpayne@68: 1.0.2 source version) 10002 is 2.V where V is the source code jpayne@68: 1.0.2a-b 10003 version, except as noted. jpayne@68: 1.0.3 10003 jpayne@68: 1.0.3a-d 10004 jpayne@68: 1.0.4 10004 jpayne@68: 1.0.4a-f 10005 jpayne@68: 1.0.5 (+ 2 patches) 10005 jpayne@68: 1.0.5a-d 10006 jpayne@68: 1.0.5e-r 10100 (not source compatible) jpayne@68: 1.0.5s-v 10006 (not binary compatible) jpayne@68: 1.0.6 (+ 3 patches) 10006 (still binary incompatible) jpayne@68: 1.0.6d-f 10007 (still binary incompatible) jpayne@68: 1.0.6g 10007 jpayne@68: 1.0.6h 10007 10.6h (testing xy.z so-numbering) jpayne@68: 1.0.6i 10007 10.6i jpayne@68: 1.0.6j 10007 2.1.0.6j (incompatible with 1.0.0) jpayne@68: 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14 (binary compatible) jpayne@68: 1.0.7beta15-18 1 10007 2.1.0.7beta15-18 (binary compatible) jpayne@68: 1.0.7rc1-2 1 10007 2.1.0.7rc1-2 (binary compatible) jpayne@68: 1.0.7 1 10007 (still compatible) jpayne@68: ... jpayne@68: 1.0.69 10 10069 10.so.0.69[.0] jpayne@68: ... jpayne@68: 1.2.59 13 10259 12.so.0.59[.0] jpayne@68: ... jpayne@68: 1.4.20 14 10420 14.so.0.20[.0] jpayne@68: ... jpayne@68: 1.5.30 15 10530 15.so.15.30[.0] jpayne@68: ... jpayne@68: 1.6.35 16 10635 16.so.16.35[.0] jpayne@68: jpayne@68: Henceforth the source version will match the shared-library minor and jpayne@68: patch numbers; the shared-library major version number will be used for jpayne@68: changes in backward compatibility, as it is intended. jpayne@68: The PNG_PNGLIB_VER macro, which is not used within libpng but is jpayne@68: available for applications, is an unsigned integer of the form XYYZZ jpayne@68: corresponding to the source version X.Y.Z (leading zeros in Y and Z). jpayne@68: Beta versions were given the previous public release number plus a jpayne@68: letter, until version 1.0.6j; from then on they were given the upcoming jpayne@68: public release number plus "betaNN" or "rcNN". jpayne@68: jpayne@68: .SH "SEE ALSO" jpayne@68: .BR "png"(5) jpayne@68: .IP jpayne@68: The PNG (Portable Network Graphics) format specification. jpayne@68: .LP jpayne@68: .B libpng jpayne@68: .IP jpayne@68: http://www.libpng.org/pub/png/libpng.html (canonical home page) jpayne@68: .br jpayne@68: https://github.com/pnggroup/libpng (canonical Git repository) jpayne@68: .br jpayne@68: https://libpng.sourceforge.io (downloadable archives) jpayne@68: .LP jpayne@68: .B zlib jpayne@68: .IP jpayne@68: https://zlib.net (canonical home page) jpayne@68: .br jpayne@68: https://github.com/madler/zlib (canonical Git repository) jpayne@68: .br jpayne@68: A copy of zlib may also be found at the same location as libpng. jpayne@68: .LP jpayne@68: In the case of any inconsistency between the PNG specification jpayne@68: and this library, the specification takes precedence. jpayne@68: jpayne@68: .SH AUTHORS jpayne@68: This man page: jpayne@68: Initially created by Glenn Randers-Pehrson. jpayne@68: Maintained by Cosmin Truta. jpayne@68: jpayne@68: The contributing authors would like to thank all those who helped jpayne@68: with testing, bug fixes, and patience. This wouldn't have been jpayne@68: possible without all of you. jpayne@68: jpayne@68: Thanks to Frank J. T. Wojcik for helping with the documentation. jpayne@68: jpayne@68: Libpng: jpayne@68: Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc. jpayne@68: Maintained by Cosmin Truta. jpayne@68: jpayne@68: Supported by the PNG development group. jpayne@68: .br jpayne@68: png-mng-implement at lists.sourceforge.net. (Subscription is required; jpayne@68: visit https://lists.sourceforge.net/lists/listinfo/png-mng-implement jpayne@68: to subscribe.) jpayne@68: jpayne@68: .\" end of man page