-.TH LIBPNG 3 "September 23, 2010"
+.TH LIBPNG 3 "April 25, 2013"
.SH NAME
-libpng \- Portable Network Graphics (PNG) Reference Library 1.4.4
+libpng \- Portable Network Graphics (PNG) Reference Library 1.6.2
.SH SYNOPSIS
-\fI\fB
-
-\fB#include <png.h>\fP
-
-\fI\fB
+\fB
+#include <png.h>\fP
\fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
-\fI\fB
-
\fBvoid png_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
-\fI\fB
+\fBvoid png_build_grayscale_palette (int \fP\fIbit_depth\fP\fB, png_colorp \fIpalette\fP\fB);\fP
-\fBvoid png_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
+\fBpng_voidp png_calloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
-\fI\fB
+\fBvoid png_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
\fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
-\fI\fB
-
\fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
-\fI\fB
-
\fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
-\fI\fB
-
\fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
-\fI\fB
-
\fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
-\fI\fB
-
\fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
-
\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
-\fI\fB
-
-\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
-
-\fI\fB
+\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
\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
-\fI\fB
+\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
-\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
-
-\fI\fB
+\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
\fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
-\fI\fB
-
\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
-\fI\fB
-
\fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
-\fI\fB
+\fBvoid png_err (png_structp \fIpng_ptr\fP\fB);\fP
\fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
-\fI\fB
-
\fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
-\fI\fB
-
\fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
-
-\fBvoid png_free_default(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
-
-\fI\fB
+\fBvoid png_free_default (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
\fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
-\fI\fB
-
-\fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
-
-\fI\fB
-
-\fBpng_uint_32 png_get_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
-
-\fI\fB
-
-\fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\fBpng_byte png_get_bit_depth (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
+\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
-\fBpng_uint_32 png_get_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_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
+\fBpng_byte png_get_channels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
+\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
-\fBpng_uint_32 png_get_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_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
+\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
-\fI\fB
+\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
-\fBpng_uint_32 png_get_chunk_cache_max (png_structp \fIpng_ptr\fP\fB);\fP
+\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
-\fI\fB
+\fBpng_uint_32 png_get_chunk_cache_max (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\fBpng_alloc_size_t png_get_chunk_malloc_max (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
+\fBpng_byte png_get_color_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
+\fBpng_uint_32 png_get_compression_buffer_size (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
+\fBpng_byte png_get_compression_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\fBpng_byte png_get_copyright (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
+\fBpng_uint_32 png_get_current_row_number \fI(png_const_structp\fP\fB);\fP
-\fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
+\fBpng_byte png_get_current_pass_number \fI(png_const_structp\fP\fB);\fP
-\fI\fB
+\fBpng_voidp png_get_error_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
+\fBpng_byte png_get_filter_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
+\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
-\fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\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
-\fI\fB
+\fBpng_byte png_get_header_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fBpng_uint_32 png_get_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
+\fBpng_byte png_get_header_version (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
+\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
-\fBpng_uint_32 png_get_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
-
-\fI\fB
-
-\fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
-
-\fI\fB
-
-\fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
-
-\fI\fB
-
-\fBpng_uint_32 png_get_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
-
-\fI\fB
-
-\fBpng_uint_32 png_get_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_charpp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
-
-\fI\fB
+\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
\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
-\fI\fB
-
-\fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\fBpng_uint_32 png_get_image_height (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
-
-\fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
-
-\fI\fB
+\fBpng_uint_32 png_get_image_width (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
\fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
-\fI\fB
-
-\fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\fBpng_byte png_get_interlace_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
+\fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP
\fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
-
-\fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
-
-\fI\fB
-
-\fBpng_alloc_size_t png_get_chunk_malloc_max (png_structp \fIpng_ptr\fP\fB);\fP
-
-\fI\fB
-
-\fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
-
-\fI\fB
-
-\fBpng_uint_32 png_get_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_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
-
-\fI\fB
-
-\fBpng_uint_32 png_get_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_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
-
-\fI\fB
-
-\fBpng_uint_32 png_get_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_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
-
-\fI\fB
+\fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP
-\fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
+\fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\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
-\fI\fB
+\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
-\fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
+\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
-\fI\fB
+\fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fBpng_uint_32 png_get_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
+\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
-\fI\fB
+\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
-\fBpng_byte png_get_rgb_to_gray_status (png_structp \fIpng_ptr)
+\fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fBpng_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
+\fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\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
-\fI\fB
+\fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fBpng_uint_32 png_get_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
+\fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
+\fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\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
-\fI\fB
+\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
-\fBpng_uint_32 png_get_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
+\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
-\fI\fB
+\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
-\fBpng_uint_32 png_get_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fI*intent\fP\fB);\fP
+\fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
+\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
-\fBpng_uint_32 png_get_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
+\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
-\fI\fB
+\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
-\fBpng_uint_32 png_get_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
+\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
-\fI\fB
-
-\fBpng_uint_32 png_get_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_color\fP\fB);\fP
-
-\fI\fB
+\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
\fB/* This function is really an inline macro. \fI*/
\fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
-\fI\fB
-
-\fBpng_uint_32 png_get_uint_31 (png_bytep \fIbuf\fP\fB);\fP
-
-\fI\fB
+\fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP
\fB/* This function is really an inline macro. \fI*/
\fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
-\fI\fB
+\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
-\fBpng_uint_32 png_get_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
+\fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
+\fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
+\fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
+\fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP
-\fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP
+\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
-\fI\fB
+\fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
+\fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
+\fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP
+\fBpng_int_32 png_get_x_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
+\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
-\fBpng_uint_32 png_get_valid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
+\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
-\fI\fB
+\fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
+\fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\fBpng_int_32 png_get_y_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
+\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
-\fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\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
-\fI\fB
+\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
-\fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\fBint png_image_begin_read_from_file (png_imagep \fP\fIimage\fP\fB, const char \fI*file_name\fP\fB);\fP
-\fI\fB
+\fBint png_image_begin_read_from_stdio (png_imagep \fP\fIimage\fP\fB, FILE* \fIfile\fP\fB);\fP
-\fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\fBint, png_image_begin_read_from_memory (png_imagep \fP\fIimage\fP\fB, png_const_voidp \fP\fImemory\fP\fB, png_size_t \fIsize\fP\fB);\fP
-\fI\fB
+\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
-\fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
+\fBvoid png_image_free (png_imagep \fIimage\fP\fB);\fP
-\fI\fB
+\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
-\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
+\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
-\fI\fB
+\fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
\fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
-\fI\fB
+\fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP
\fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
-\fI\fB
-
-\fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
+\fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
-\fI\fB
+\fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
-\fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
-
-\fI\fB
-
-\fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
-
-\fI\fB
+\fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP
\fBvoid png_process_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fIbuffer\fP\fB, png_size_t \fIbuffer_size\fP\fB);\fP
-\fI\fB
+\fBpng_size_t png_process_data_pause \fP\fI(png_structp\fP\fB, int \fIsave\fP\fB);\fP
-\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
+\fBpng_uint_32 png_process_data_skip \fI(png_structp\fP\fB);\fP
-\fI\fB
+\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
\fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
-
\fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
-\fI\fB
-
\fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
-
\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
-\fI\fB
-
\fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
-\fI\fB
-
\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
-\fI\fB
-
\fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
-
-\fBpng_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
+\fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
+\fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
\fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
-\fI\fB
-
\fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
-\fI\fB
-
\fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
-\fI\fB
+\fBvoid png_set_alpha_mode (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, double \fIoutput_gamma\fP\fB);\fP
+
+\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
\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
-\fI\fB
+\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
-\fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
+\fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
-\fI\fB
+\fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
\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
-\fI\fB
+\fBvoid png_set_check_for_invalid_index(png_structrp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
\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
-\fI\fB
-
\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
-\fI\fB
+\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
-\fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
+\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
-\fI\fB
+\fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
\fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
-\fI\fB
-
\fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
-\fI\fB
-
\fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
-\fI\fB
-
\fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
-\fI\fB
-
\fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
-\fI\fB
-
\fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
-\fI\fB
-
\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
-\fI\fB
-
\fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
+\fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP
-\fBvoid png_set_expand_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
-
-\fI\fB
+\fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
\fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
-\fI\fB
-
\fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
-\fI\fB
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\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
-\fI\fB
+\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
\fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
-\fI\fB
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\fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
-\fI\fB
+\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
\fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
-\fI\fB
-
\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
-\fI\fB
-
-\fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
-
-\fI\fB
+\fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
\fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
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\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
-\fI\fB
-
-\fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_charp \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
-
-\fI\fB
+\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
\fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
-
\fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
-\fI\fB
-
\fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
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\fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
-
\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
-\fI\fB
-
\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
-\fI\fB
-
\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
-\fI\fB
-
\fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
-\fI\fB
+\fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
-\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
-
-\fI\fB
+\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
\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
-\fI\fB
-
\fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
-
\fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
-
-\fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
-
-\fI\fB
+\fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
\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
-\fI\fB
-
\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
-\fI\fB
-
\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
-\fI\fB
-
\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
-\fI\fB
-
\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
-\fI\fB
-
\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
-\fI\fB
-
\fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
-\fI\fB
+\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
\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
-\fI\fB
-
\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
-\fI\fB
-
-\fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_fixed_point \fP\fIred\fP\fB, png_fixed_point \fIgreen\fP\fB);\fP
-
-\fI\fB
+\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
\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
-\fI\fB
-
\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
-\fI\fB
+\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
-\fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
+\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
-\fI\fB
+\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
-\fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
+\fBvoid png_set_scale_16 (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
+\fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
\fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
-\fI\fB
-
\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
-\fI\fB
-
-\fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
+\fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
-\fI\fB
-
-\fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
-
-\fI\fB
+\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
\fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
-
\fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
+\fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP
\fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
-
\fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
-
\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
-\fI\fB
-
-\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
-
-\fI\fB
-
-\fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_color\fP\fB);\fP
+\fBvoid png_set_text_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
-\fI\fB
+\fBvoid png_set_text_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
-\fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
+\fBvoid png_set_text_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
-\fI\fB
+\fBvoid png_set_text_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
-\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
+\fBvoid \fP\fIpng_set_text_compression_method\fP\fB, (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod)\fP\fB);\fP
-\fI\fB
+\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
-\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
+\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
-\fI\fB
+\fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP
-\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
+\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
-\fI\fB
+\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
\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
-\fI\fB
-
\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
-\fI\fB
-
\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
-\fI\fB
-
\fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
-\fI\fB
-
\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
-\fI\fB
-
-\fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
-
-\fI\fB
-
\fBint png_sig_cmp (png_bytep \fP\fIsig\fP\fB, png_size_t \fP\fIstart\fP\fB, png_size_t \fInum_to_check\fP\fB);\fP
-\fI\fB
-
\fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
-
\fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
-\fI\fB
-
\fBvoid png_write_chunk (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
-\fI\fB
-
\fBvoid png_write_chunk_data (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
-\fI\fB
-
\fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
-
\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
-\fI\fB
-
\fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
-
\fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
-
\fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
-\fI\fB
-
\fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
-
\fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
-\fI\fB
-
\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
-\fI\fB
-
\fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
-\fI\fB
-
\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
-\fI\fB
-
\fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
-\fI\fB
-
-\fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
-
-\fI\fB
-
-\fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
-
-\fI\fB
-
.SH DESCRIPTION
The
.I libpng
the Portable Network Graphics (PNG) format image files. It uses the
.IR zlib(3)
compression library.
-Following is a copy of the libpng.txt file that accompanies libpng.
+Following is a copy of the libpng-manual.txt file that accompanies libpng.
.SH LIBPNG.TXT
-libpng.txt - A description on how to use and modify libpng
+libpng-manual.txt - A description on how to use and modify libpng
- libpng version 1.4.4 - September 23, 2010
+ libpng version 1.6.2 - April 25, 2013
Updated and distributed by Glenn Randers-Pehrson
<glennrp at users.sourceforge.net>
- Copyright (c) 1998-2010 Glenn Randers-Pehrson
+ Copyright (c) 1998-2013 Glenn Randers-Pehrson
This document is released under the libpng license.
For conditions of distribution and use, see the disclaimer
Based on:
- libpng versions 0.97, January 1998, through 1.4.4 - September 23, 2010
+ libpng versions 0.97, January 1998, through 1.6.2 - April 25, 2013
Updated and distributed by Glenn Randers-Pehrson
- Copyright (c) 1998-2010 Glenn Randers-Pehrson
+ Copyright (c) 1998-2013 Glenn Randers-Pehrson
libpng 1.0 beta 6 version 0.96 May 28, 1997
Updated and distributed by Andreas Dilger
Copyright (c) 1995, 1996 Frank J. T. Wojcik
December 18, 1995 & January 20, 1996
+ TABLE OF CONTENTS
+
+ I. Introduction
+ II. Structures
+ III. Reading
+ IV. Writing
+ V. Simplified API
+ VI. Modifying/Customizing libpng
+ VII. MNG support
+ VIII. Changes to Libpng from version 0.88
+ IX. Changes to Libpng from version 1.0.x to 1.2.x
+ X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
+ XI. Changes to Libpng from version 1.4.x to 1.5.x
+ XII. Changes to Libpng from version 1.5.x to 1.6.x
+ XIII. Detecting libpng
+ XIV. Source code repository
+ XV. Coding style
+ XVI. Y2K Compliance in libpng
+
.SH I. Introduction
This file describes how to use and modify the PNG reference library
file format in application programs.
The PNG specification (second edition), November 2003, is available as
-a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
+a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2004 (E)) at
<http://www.w3.org/TR/2003/REC-PNG-20031110/
The W3C and ISO documents have identical technical content.
.SH II. Structures
There are two main structures that are important to libpng, png_struct
-and png_info. The first, png_struct, is an internal structure that
-will not, for the most part, be used by a user except as the first
-variable passed to every libpng function call.
+and png_info. Both are internal structures that are no longer exposed
+in the libpng interface (as of libpng 1.5.0).
The png_info structure is designed to provide information about the
PNG file. At one time, the fields of png_info were intended to be
directly accessible to the user. However, this tended to cause problems
with applications using dynamically loaded libraries, and as a result
a set of interface functions for png_info (the png_get_*() and png_set_*()
-functions) was developed. The fields of png_info are still available for
-older applications, but it is suggested that applications use the new
-interfaces if at all possible.
-
-Applications that do make direct access to the members of png_struct (except
-for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
-and applications that make direct access to the members of png_info must
-be recompiled if they were compiled or loaded with libpng version 1.0.6,
-in which the members were in a different order. In version 1.0.7, the
-members of the png_info structure reverted to the old order, as they were
-in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
-structures are going to be hidden, and the contents of the structures will
-only be accessible through the png_get/png_set functions.
+functions) was developed, and direct access to the png_info fields was
+deprecated..
+
+The png_struct structure is the object used by the library to decode a
+single image. As of 1.5.0 this structure is also not exposed.
+
+Almost all libpng APIs require a pointer to a png_struct as the first argument.
+Many (in particular the png_set and png_get APIs) also require a pointer
+to png_info as the second argument. Some application visible macros
+defined in png.h designed for basic data access (reading and writing
+integers in the PNG format) don't take a png_info pointer, but it's almost
+always safe to assume that a (png_struct*) has to be passed to call an API
+function.
+
+You can have more than one png_info structure associated with an image,
+as illustrated in pngtest.c, one for information valid prior to the
+IDAT chunks and another (called "end_info" below) for things after them.
The png.h header file is an invaluable reference for programming with libpng.
And while I'm on the topic, make sure you include the libpng header file:
#include <png.h>
+and also (as of libpng-1.5.0) the zlib header file, if you need it:
+
+#include <zlib.h>
+
+.SS Types
+
+The png.h header file defines a number of integral types used by the
+APIs. Most of these are fairly obvious; for example types corresponding
+to integers of particular sizes and types for passing color values.
+
+One exception is how non-integral numbers are handled. For application
+convenience most APIs that take such numbers have C (double) arguments;
+however, internally PNG, and libpng, use 32 bit signed integers and encode
+the value by multiplying by 100,000. As of libpng 1.5.0 a convenience
+macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point)
+which is simply (png_int_32).
+
+All APIs that take (double) arguments also have a matching API that
+takes the corresponding fixed point integer arguments. The fixed point
+API has the same name as the floating point one with "_fixed" appended.
+The actual range of values permitted in the APIs is frequently less than
+the full range of (png_fixed_point) (-21474 to +21474). When APIs require
+a non-negative argument the type is recorded as png_uint_32 above. Consult
+the header file and the text below for more information.
+
+Special care must be take with sCAL chunk handling because the chunk itself
+uses non-integral values encoded as strings containing decimal floating point
+numbers. See the comments in the header file.
+
+.SS Configuration
+
+The main header file function declarations are frequently protected by C
+preprocessing directives of the form:
+
+ #ifdef PNG_feature_SUPPORTED
+ declare-function
+ #endif
+ ...
+ #ifdef PNG_feature_SUPPORTED
+ use-function
+ #endif
+
+The library can be built without support for these APIs, although a
+standard build will have all implemented APIs. Application programs
+should check the feature macros before using an API for maximum
+portability. From libpng 1.5.0 the feature macros set during the build
+of libpng are recorded in the header file "pnglibconf.h" and this file
+is always included by png.h.
+
+If you don't need to change the library configuration from the default, skip to
+the next section ("Reading").
+
+Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all
+of the build project files in the 'projects' directory simply copy
+scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build
+systems do not permit easy auto-configuration of the library - they only
+support the default configuration.
+
+The easiest way to make minor changes to the libpng configuration when
+auto-configuration is supported is to add definitions to the command line
+using (typically) CPPFLAGS. For example:
+
+CPPFLAGS=-DPNG_NO_FLOATING_ARITHMETIC
+
+will change the internal libpng math implementation for gamma correction and
+other arithmetic calculations to fixed point, avoiding the need for fast
+floating point support. The result can be seen in the generated pnglibconf.h -
+make sure it contains the changed feature macro setting.
+
+If you need to make more extensive configuration changes - more than one or two
+feature macro settings - you can either add -DPNG_USER_CONFIG to the build
+command line and put a list of feature macro settings in pngusr.h or you can set
+DFA_XTRA (a makefile variable) to a file containing the same information in the
+form of 'option' settings.
+
+A. Changing pnglibconf.h
+
+A variety of methods exist to build libpng. Not all of these support
+reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be
+rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand.
+
+Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to
+pnglibconf.h and changing the lines defining the supported features, paying
+very close attention to the 'option' information in scripts/pnglibconf.dfa
+that describes those features and their requirements. This is easy to get
+wrong.
+
+B. Configuration using DFA_XTRA
+
+Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later
+variant such as 'nawk' or 'gawk', is available. The configure build will
+automatically find an appropriate awk and build pnglibconf.h.
+The scripts/pnglibconf.mak file contains a set of make rules for doing the
+same thing if configure is not used, and many of the makefiles in the scripts
+directory use this approach.
+
+When rebuilding simply write a new file containing changed options and set
+DFA_XTRA to the name of this file. This causes the build to append the new file
+to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines
+of the following forms:
+
+everything = off
+
+This turns all optional features off. Include it at the start of pngusr.dfa to
+make it easier to build a minimal configuration. You will need to turn at least
+some features on afterward to enable either reading or writing code, or both.
+
+option feature on
+option feature off
+
+Enable or disable a single feature. This will automatically enable other
+features required by a feature that is turned on or disable other features that
+require a feature which is turned off. Conflicting settings will cause an error
+message to be emitted by awk.
+
+setting feature default value
+
+Changes the default value of setting 'feature' to 'value'. There are a small
+number of settings listed at the top of pnglibconf.h, they are documented in the
+source code. Most of these values have performance implications for the library
+but most of them have no visible effect on the API. Some can also be overridden
+from the API.
+
+This method of building a customized pnglibconf.h is illustrated in
+contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and
+pngusr.dfa in these directories.
+
+C. Configuration using PNG_USR_CONFIG
+
+If -DPNG_USR_CONFIG is added to the CFLAGS when pnglibconf.h is built the file
+pngusr.h will automatically be included before the options in
+scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only
+macro definitions turning features on or off or setting settings.
+
+Apart from the global setting "everything = off" all the options listed above
+can be set using macros in pngusr.h:
+
+#define PNG_feature_SUPPORTED
+
+is equivalent to:
+
+option feature on
+
+#define PNG_NO_feature
+
+is equivalent to:
+
+option feature off
+
+#define PNG_feature value
+
+is equivalent to:
+
+setting feature default value
+
+Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the
+pngusr file you supply override the contents of scripts/pnglibconf.dfa
+
+If confusing or incomprehensible behavior results it is possible to
+examine the intermediate file pnglibconf.dfn to find the full set of
+dependency information for each setting and option. Simply locate the
+feature in the file and read the C comments that precede it.
+
+This method is also illustrated in the contrib/pngminim/* makefiles and
+pngusr.h.
+
.SH III. Reading
We'll now walk you through the possible functions to call when reading
FILE *fp = fopen(file_name, "rb");
if (!fp)
{
- return (ERROR);
+ return (ERROR);
}
+
fread(header, 1, number, fp);
is_png = !png_sig_cmp(header, 0, number);
+
if (!is_png)
{
- return (NOT_PNG);
+ return (NOT_PNG);
}
create the structure, so your application should check for that.
png_structp png_ptr = png_create_read_struct
- (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
+ (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
user_error_fn, user_warning_fn);
+
if (!png_ptr)
- return (ERROR);
+ return (ERROR);
png_infop info_ptr = png_create_info_struct(png_ptr);
+
if (!info_ptr)
{
- png_destroy_read_struct(&png_ptr,
+ png_destroy_read_struct(&png_ptr,
(png_infopp)NULL, (png_infopp)NULL);
- return (ERROR);
- }
-
- png_infop end_info = png_create_info_struct(png_ptr);
- if (!end_info)
- {
- png_destroy_read_struct(&png_ptr, &info_ptr,
- (png_infopp)NULL);
- return (ERROR);
+ return (ERROR);
}
If you want to use your own memory allocation routines,
-define PNG_USER_MEM_SUPPORTED and use
+use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use
png_create_read_struct_2() instead of png_create_read_struct():
png_structp png_ptr = png_create_read_struct_2
- (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
+ (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
user_error_fn, user_warning_fn, (png_voidp)
user_mem_ptr, user_malloc_fn, user_free_fn);
When libpng encounters an error, it expects to longjmp back
to your routine. Therefore, you will need to call setjmp and pass
your png_jmpbuf(png_ptr). If you read the file from different
-routines, you will need to update the jmpbuf field every time you enter
+routines, you will need to update the longjmp buffer every time you enter
a new routine that will call a png_*() function.
See your documentation of setjmp/longjmp for your compiler for more
if (setjmp(png_jmpbuf(png_ptr)))
{
- png_destroy_read_struct(&png_ptr, &info_ptr,
+ png_destroy_read_struct(&png_ptr, &info_ptr,
&end_info);
- fclose(fp);
- return (ERROR);
+ fclose(fp);
+ return (ERROR);
}
+Pass (png_infopp)NULL instead of &end_info if you didn't create
+an end_info structure.
+
If you would rather avoid the complexity of setjmp/longjmp issues,
you can compile libpng with PNG_NO_SETJMP, in which case
errors will result in a call to PNG_ABORT() which defaults to abort().
is changed immediately and the buffer is reallocated immediately,
instead of setting a flag to be acted upon later.
+If you want CRC errors to be handled in a different manner than
+the default, use
+
+ png_set_crc_action(png_ptr, crit_action, ancil_action);
+
+The values for png_set_crc_action() say how libpng is to handle CRC errors in
+ancillary and critical chunks, and whether to use the data contained
+therein. Note that it is impossible to "discard" data in a critical
+chunk.
+
+Choices for (int) crit_action are
+ PNG_CRC_DEFAULT 0 error/quit
+ PNG_CRC_ERROR_QUIT 1 error/quit
+ PNG_CRC_WARN_USE 3 warn/use data
+ PNG_CRC_QUIET_USE 4 quiet/use data
+ PNG_CRC_NO_CHANGE 5 use the current value
+
+Choices for (int) ancil_action are
+ PNG_CRC_DEFAULT 0 error/quit
+ PNG_CRC_ERROR_QUIT 1 error/quit
+ PNG_CRC_WARN_DISCARD 2 warn/discard data
+ PNG_CRC_WARN_USE 3 warn/use data
+ PNG_CRC_QUIET_USE 4 quiet/use data
+ PNG_CRC_NO_CHANGE 5 use the current value
+
.SS Setting up callback code
You can set up a callback function to handle any unknown chunks in the
input stream. You must supply the function
- read_chunk_callback(png_ptr ptr,
+ read_chunk_callback(png_structp png_ptr,
png_unknown_chunkp chunk);
{
/* The unknown chunk structure contains your
png_get_user_chunk_ptr(png_ptr);
If you call the png_set_read_user_chunk_fn() function, then all unknown
-chunks will be saved when read, in case your callback function will need
-one or more of them. This behavior can be changed with the
-png_set_keep_unknown_chunks() function, described below.
+chunks which the callback does not handle will be saved when read. You can
+cause them to be discarded by returning '1' ("handled") instead of '0'. This
+behavior will change in libpng 1.7 and the default handling set by the
+png_set_keep_unknown_chunks() function, described below, will be used when the
+callback returns 0. If you want the existing behavior you should set the global
+default to PNG_HANDLE_CHUNK_IF_SAFE now; this is compatible with all current
+versions of libpng and with 1.7. Libpng 1.6 issues a warning if you keep the
+default, or PNG_HANDLE_CHUNK_NEVER, and the callback returns 0.
At this point, you can set up a callback function that will be
called after each row has been read, which you can use to control
a progress meter or the like. It's demonstrated in pngtest.c.
You must supply a function
- void read_row_callback(png_ptr ptr, png_uint_32 row,
- int pass);
+ void read_row_callback(png_structp png_ptr,
+ png_uint_32 row, int pass);
{
/* put your code here */
}
png_set_read_status_fn(png_ptr, read_row_callback);
+When this function is called the row has already been completely processed and
+the 'row' and 'pass' refer to the next row to be handled. For the
+non-interlaced case the row that was just handled is simply one less than the
+passed in row number, and pass will always be 0. For the interlaced case the
+same applies unless the row value is 0, in which case the row just handled was
+the last one from one of the preceding passes. Because interlacing may skip a
+pass you cannot be sure that the preceding pass is just 'pass-1', if you really
+need to know what the last pass is record (row,pass) from the callback and use
+the last recorded value each time.
+
+As with the user transform you can find the output row using the
+PNG_ROW_FROM_PASS_ROW macro.
+
.SS Unknown-chunk handling
Now you get to set the way the library processes unknown chunks in the
png_set_keep_unknown_chunks(png_ptr, keep,
chunk_list, num_chunks);
+
keep - 0: default unknown chunk handling
1: ignore; do not keep
2: keep only if safe-to-copy
3: keep even if unsafe-to-copy
+
You can use these definitions:
PNG_HANDLE_CHUNK_AS_DEFAULT 0
PNG_HANDLE_CHUNK_NEVER 1
PNG_HANDLE_CHUNK_IF_SAFE 2
PNG_HANDLE_CHUNK_ALWAYS 3
+
chunk_list - list of chunks affected (a byte string,
five bytes per chunk, NULL or '\0' if
- num_chunks is 0)
+ num_chunks is positive; ignored if
+ numchunks <= 0).
+
num_chunks - number of chunks affected; if 0, all
- unknown chunks are affected. If nonzero,
- only the chunks in the list are affected
+ unknown chunks are affected. If positive,
+ only the chunks in the list are affected,
+ and if negative all unknown chunks and
+ all known chunks except for the IHDR,
+ PLTE, tRNS, IDAT, and IEND chunks are
+ affected.
Unknown chunks declared in this way will be saved as raw data onto a
list of png_unknown_chunk structures. If a chunk that is normally
instances of png_set_keep_unknown_chunks(), the final instance will
take precedence. The IHDR and IEND chunks should not be named in
chunk_list; if they are, libpng will process them normally anyway.
+If you know that your application will never make use of some particular
+chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below.
Here is an example of the usage of png_set_keep_unknown_chunks(),
where the private "vpAg" chunk will later be processed by a user chunk
...
#if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
- /* ignore all unknown chunks: */
- png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
+ /* ignore all unknown chunks
+ * (use global setting "2" for libpng16 and earlier):
+ */
+ png_set_keep_unknown_chunks(read_ptr, 2, NULL, 0);
+
/* except for vpAg: */
png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
+
/* also ignore unused known chunks: */
png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
- (int)sizeof(unused_chunks)/5);
+ (int)(sizeof unused_chunks)/5);
#endif
.SS User limits
Since very few applications really need to process such large images,
we have imposed an arbitrary 1-million limit on rows and columns.
Larger images will be rejected immediately with a png_error() call. If
-you wish to override this limit, you can use
+you wish to change this limit, you can use
png_set_user_limits(png_ptr, width_max, height_max);
You should put this statement after you create the PNG structure and
before calling png_read_info(), png_read_png(), or png_process_data().
+
+When writing a PNG datastream, put this statement before calling
+png_write_info() or png_write_png().
+
If you need to retrieve the limits that are being applied, use
width_max = png_get_user_width_max(png_ptr);
chunk_cache_max = png_get_chunk_cache_max(png_ptr);
-This limit also applies to the number of buffers that can be allocated
-by png_decompress_chunk() while decompressing iTXt, zTXt, and iCCP chunks.
-
You can also set a limit on the amount of memory that a compressed chunk
other than IDAT can occupy, with
Any chunks that would cause either of these limits to be exceeded will
be ignored.
+.SS Information about your system
+
+If you intend to display the PNG or to incorporate it in other image data you
+need to tell libpng information about your display or drawing surface so that
+libpng can convert the values in the image to match the display.
+
+From libpng-1.5.4 this information can be set before reading the PNG file
+header. In earlier versions png_set_gamma() existed but behaved incorrectly if
+called before the PNG file header had been read and png_set_alpha_mode() did not
+exist.
+
+If you need to support versions prior to libpng-1.5.4 test the version number
+as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures
+described in the appropriate manual page.
+
+You give libpng the encoding expected by your system expressed as a 'gamma'
+value. You can also specify a default encoding for the PNG file in
+case the required information is missing from the file. By default libpng
+assumes that the PNG data matches your system, to keep this default call:
+
+ png_set_gamma(png_ptr, screen_gamma, 1/screen_gamma/*file gamma*/);
+
+or you can use the fixed point equivalent:
+
+ png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma,
+ PNG_FP_1/screen_gamma);
+
+If you don't know the gamma for your system it is probably 2.2 - a good
+approximation to the IEC standard for display systems (sRGB). If images are
+too contrasty or washed out you got the value wrong - check your system
+documentation!
+
+Many systems permit the system gamma to be changed via a lookup table in the
+display driver, a few systems, including older Macs, change the response by
+default. As of 1.5.4 three special values are available to handle common
+situations:
+
+ PNG_DEFAULT_sRGB: Indicates that the system conforms to the
+ IEC 61966-2-1 standard. This matches almost
+ all systems.
+ PNG_GAMMA_MAC_18: Indicates that the system is an older
+ (pre Mac OS 10.6) Apple Macintosh system with
+ the default settings.
+ PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates
+ that the system expects data with no gamma
+ encoding.
+
+You would use the linear (unencoded) value if you need to process the pixel
+values further because this avoids the need to decode and reencode each
+component value whenever arithmetic is performed. A lot of graphics software
+uses linear values for this reason, often with higher precision component values
+to preserve overall accuracy.
+
+The second thing you may need to tell libpng about is how your system handles
+alpha channel information. Some, but not all, PNG files contain an alpha
+channel. To display these files correctly you need to compose the data onto a
+suitable background, as described in the PNG specification.
+
+Libpng only supports composing onto a single color (using png_set_background;
+see below). Otherwise you must do the composition yourself and, in this case,
+you may need to call png_set_alpha_mode:
+
+ #if PNG_LIBPNG_VER >= 10504
+ png_set_alpha_mode(png_ptr, mode, screen_gamma);
+ #else
+ png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma);
+ #endif
+
+The screen_gamma value is the same as the argument to png_set_gamma; however,
+how it affects the output depends on the mode. png_set_alpha_mode() sets the
+file gamma default to 1/screen_gamma, so normally you don't need to call
+png_set_gamma. If you need different defaults call png_set_gamma() before
+png_set_alpha_mode() - if you call it after it will override the settings made
+by png_set_alpha_mode().
+
+The mode is as follows:
+
+ PNG_ALPHA_PNG: The data is encoded according to the PNG specification. Red,
+green and blue, or gray, components are gamma encoded color
+values and are not premultiplied by the alpha value. The
+alpha value is a linear measure of the contribution of the
+pixel to the corresponding final output pixel.
+
+You should normally use this format if you intend to perform
+color correction on the color values; most, maybe all, color
+correction software has no handling for the alpha channel and,
+anyway, the math to handle pre-multiplied component values is
+unnecessarily complex.
+
+Before you do any arithmetic on the component values you need
+to remove the gamma encoding and multiply out the alpha
+channel. See the PNG specification for more detail. It is
+important to note that when an image with an alpha channel is
+scaled, linear encoded, pre-multiplied component values must
+be used!
+
+The remaining modes assume you don't need to do any further color correction or
+that if you do, your color correction software knows all about alpha (it
+probably doesn't!)
+
+ PNG_ALPHA_STANDARD: The data libpng produces
+is encoded in the standard way
+assumed by most correctly written graphics software.
+The gamma encoding will be removed by libpng and the
+linear component values will be pre-multiplied by the
+alpha channel.
+
+With this format the final image must be re-encoded to
+match the display gamma before the image is displayed.
+If your system doesn't do that, yet still seems to
+perform arithmetic on the pixels without decoding them,
+it is broken - check out the modes below.
+
+With PNG_ALPHA_STANDARD libpng always produces linear
+component values, whatever screen_gamma you supply. The
+screen_gamma value is, however, used as a default for
+the file gamma if the PNG file has no gamma information.
+
+If you call png_set_gamma() after png_set_alpha_mode() you
+will override the linear encoding. Instead the
+pre-multiplied pixel values will be gamma encoded but
+the alpha channel will still be linear. This may
+actually match the requirements of some broken software,
+but it is unlikely.
+
+While linear 8-bit data is often used it has
+insufficient precision for any image with a reasonable
+dynamic range. To avoid problems, and if your software
+supports it, use png_set_expand_16() to force all
+components to 16 bits.
+
+ PNG_ALPHA_OPTIMIZED: This mode is the same
+as PNG_ALPHA_STANDARD except that
+completely opaque pixels are gamma encoded according to
+the screen_gamma value. Pixels with alpha less than 1.0
+will still have linear components.
+
+Use this format if you have control over your
+compositing software and so don't do other arithmetic
+(such as scaling) on the data you get from libpng. Your
+compositing software can simply copy opaque pixels to
+the output but still has linear values for the
+non-opaque pixels.
+
+In normal compositing, where the alpha channel encodes
+partial pixel coverage (as opposed to broad area
+translucency), the inaccuracies of the 8-bit
+representation of non-opaque pixels are irrelevant.
+
+You can also try this format if your software is broken;
+it might look better.
+
+ PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD;
+however, all component values,
+including the alpha channel are gamma encoded. This is
+an appropriate format to try if your software, or more
+likely hardware, is totally broken, i.e., if it performs
+linear arithmetic directly on gamma encoded values.
+
+In most cases of broken software or hardware the bug in the final display
+manifests as a subtle halo around composited parts of the image. You may not
+even perceive this as a halo; the composited part of the image may simply appear
+separate from the background, as though it had been cut out of paper and pasted
+on afterward.
+
+If you don't have to deal with bugs in software or hardware, or if you can fix
+them, there are three recommended ways of using png_set_alpha_mode():
+
+ png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG,
+ screen_gamma);
+
+You can do color correction on the result (libpng does not currently
+support color correction internally). When you handle the alpha channel
+you need to undo the gamma encoding and multiply out the alpha.
+
+ png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD,
+ screen_gamma);
+ png_set_expand_16(png_ptr);
+
+If you are using the high level interface, don't call png_set_expand_16();
+instead pass PNG_TRANSFORM_EXPAND_16 to the interface.
+
+With this mode you can't do color correction, but you can do arithmetic,
+including composition and scaling, on the data without further processing.
+
+ png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED,
+ screen_gamma);
+
+You can avoid the expansion to 16-bit components with this mode, but you
+lose the ability to scale the image or perform other linear arithmetic.
+All you can do is compose the result onto a matching output. Since this
+mode is libpng-specific you also need to write your own composition
+software.
+
+If you don't need, or can't handle, the alpha channel you can call
+png_set_background() to remove it by compositing against a fixed color. Don't
+call png_set_strip_alpha() to do this - it will leave spurious pixel values in
+transparent parts of this image.
+
+ png_set_background(png_ptr, &background_color,
+ PNG_BACKGROUND_GAMMA_SCREEN, 0, 1);
+
+The background_color is an RGB or grayscale value according to the data format
+libpng will produce for you. Because you don't yet know the format of the PNG
+file, if you call png_set_background at this point you must arrange for the
+format produced by libpng to always have 8-bit or 16-bit components and then
+store the color as an 8-bit or 16-bit color as appropriate. The color contains
+separate gray and RGB component values, so you can let libpng produce gray or
+RGB output according to the input format, but low bit depth grayscale images
+must always be converted to at least 8-bit format. (Even though low bit depth
+grayscale images can't have an alpha channel they can have a transparent
+color!)
+
+You set the transforms you need later, either as flags to the high level
+interface or libpng API calls for the low level interface. For reference the
+settings and API calls required are:
+
+8-bit values:
+ PNG_TRANSFORM_SCALE_16 | PNG_EXPAND
+ png_set_expand(png_ptr); png_set_scale_16(png_ptr);
+
+ If you must get exactly the same inaccurate results
+ produced by default in versions prior to libpng-1.5.4,
+ use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr)
+ instead.
+
+16-bit values:
+ PNG_TRANSFORM_EXPAND_16
+ png_set_expand_16(png_ptr);
+
+In either case palette image data will be expanded to RGB. If you just want
+color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr)
+to the list.
+
+Calling png_set_background before the PNG file header is read will not work
+prior to libpng-1.5.4. Because the failure may result in unexpected warnings or
+errors it is therefore much safer to call png_set_background after the head has
+been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be
+used with the high level interface.
+
.SS The high-level read interface
At this point there are two ways to proceed; through the high-level
you want to do are limited to the following set:
PNG_TRANSFORM_IDENTITY No transformation
- PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
- 8 bits
+ PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to
+ 8-bit accurately
+ PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to
+ 8-bit less accurately
PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
samples to bytes
PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
to RGB (or GA to RGBA)
+ PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits
(This excludes setting a background color, doing gamma transformation,
quantizing, and setting filler.) If this is the case, simply do this:
If you know your image size and pixel size ahead of time, you can allocate
row_pointers prior to calling png_read_png() with
- if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
+ if (height > PNG_UINT_32_MAX/(sizeof (png_byte)))
png_error (png_ptr,
- "Image is too tall to process in memory");
+ "Image is too tall to process in memory");
+
if (width > PNG_UINT_32_MAX/pixel_size)
png_error (png_ptr,
- "Image is too wide to process in memory");
+ "Image is too wide to process in memory");
+
row_pointers = png_malloc(png_ptr,
- height*png_sizeof(png_bytep));
+ height*(sizeof (png_bytep)));
+
for (int i=0; i<height, i++)
row_pointers[i]=NULL; /* security precaution */
+
for (int i=0; i<height, i++)
row_pointers[i]=png_malloc(png_ptr,
- width*pixel_size);
+ width*pixel_size);
+
png_set_rows(png_ptr, info_ptr, &row_pointers);
Alternatively you could allocate your image in one big block and define
row_pointers (and row_pointers[i], if they were separately allocated).
If you don't allocate row_pointers ahead of time, png_read_png() will
-do it, and it'll be free'ed when you call png_destroy_*().
+do it, and it'll be free'ed by libpng when you call png_destroy_*().
.SS The low-level read interface
This will process all chunks up to but not including the image data.
+This also copies some of the data from the PNG file into the decode structure
+for use in later transformations. Important information copied in is:
+
+1) The PNG file gamma from the gAMA chunk. This overwrites the default value
+provided by an earlier call to png_set_gamma or png_set_alpha_mode.
+
+2) Prior to libpng-1.5.4 the background color from a bKGd chunk. This
+damages the information provided by an earlier call to png_set_background
+resulting in unexpected behavior. Libpng-1.5.4 no longer does this.
+
+3) The number of significant bits in each component value. Libpng uses this to
+optimize gamma handling by reducing the internal lookup table sizes.
+
+4) The transparent color information from a tRNS chunk. This can be modified by
+a later call to png_set_tRNS.
+
.SS Querying the info structure
Functions are used to get the information from the info_ptr once it
width - holds the width of the image
in pixels (up to 2^31).
+
height - holds the height of the image
in pixels (up to 2^31).
+
bit_depth - holds the bit depth of one of the
image channels. (valid values are
1, 2, 4, 8, 16 and depend also on
the color_type. See also
significant bits (sBIT) below).
+
color_type - describes which color/alpha channels
are present.
PNG_COLOR_TYPE_GRAY
PNG_COLOR_MASK_COLOR
PNG_COLOR_MASK_ALPHA
+ interlace_type - (PNG_INTERLACE_NONE or
+ PNG_INTERLACE_ADAM7)
+
+ compression_type - (must be PNG_COMPRESSION_TYPE_BASE
+ for PNG 1.0)
+
filter_method - (must be PNG_FILTER_TYPE_BASE
for PNG 1.0, and can also be
PNG_INTRAPIXEL_DIFFERENCING if
the PNG datastream is embedded in
a MNG-1.0 datastream)
- compression_type - (must be PNG_COMPRESSION_TYPE_BASE
- for PNG 1.0)
- interlace_type - (PNG_INTERLACE_NONE or
- PNG_INTERLACE_ADAM7)
Any or all of interlace_type, compression_type, or
filter_method can be NULL if you are
width = png_get_image_width(png_ptr,
info_ptr);
+
height = png_get_image_height(png_ptr,
info_ptr);
+
bit_depth = png_get_bit_depth(png_ptr,
info_ptr);
+
color_type = png_get_color_type(png_ptr,
info_ptr);
- filter_method = png_get_filter_type(png_ptr,
+
+ interlace_type = png_get_interlace_type(png_ptr,
info_ptr);
+
compression_type = png_get_compression_type(png_ptr,
info_ptr);
- interlace_type = png_get_interlace_type(png_ptr,
+
+ filter_method = png_get_filter_type(png_ptr,
info_ptr);
channels = png_get_channels(png_ptr, info_ptr);
+
channels - number of channels of info for the
color type (valid values are 1 (GRAY,
PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
4 (RGB_ALPHA or RGB + filler byte))
+
rowbytes = png_get_rowbytes(png_ptr, info_ptr);
+
rowbytes - number of bytes needed to hold a row
signature = png_get_signature(png_ptr, info_ptr);
+
signature - holds the signature read from the
file (if any). The data is kept in
the same offset it would be if the
png_get_<chunk> are set directly if they are simple data types, or a
pointer into the info_ptr is returned for any complex types.
+The colorspace data from gAMA, cHRM, sRGB, iCCP, and sBIT chunks
+is simply returned to give the application information about how the
+image was encoded. Libpng itself only does transformations using the file
+gamma when combining semitransparent pixels with the background color, and,
+since libpng-1.6.0, when converting between 8-bit sRGB and 16-bit linear pixels
+within the simplified API. Libpng also uses the file gamma when converting
+RGB to gray, beginning with libpng-1.0.5, if the application calls
+png_set_rgb_to_gray()).
+
png_get_PLTE(png_ptr, info_ptr, &palette,
&num_palette);
+
palette - the palette for the file
(array of png_color)
+
num_palette - number of entries in the palette
- png_get_gAMA(png_ptr, info_ptr, &gamma);
- gamma - the gamma the file is written
- at (PNG_INFO_gAMA)
+ png_get_gAMA(png_ptr, info_ptr, &file_gamma);
+ png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma);
+
+ file_gamma - the gamma at which the file is
+ written (PNG_INFO_gAMA)
+
+ int_file_gamma - 100,000 times the gamma at which the
+ file is written
+
+ png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x,
+ &red_y, &green_x, &green_y, &blue_x, &blue_y)
+ png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z,
+ &green_X, &green_Y, &green_Z, &blue_X, &blue_Y,
+ &blue_Z)
+ png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x,
+ &int_white_y, &int_red_x, &int_red_y,
+ &int_green_x, &int_green_y, &int_blue_x,
+ &int_blue_y)
+ png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y,
+ &int_red_Z, &int_green_X, &int_green_Y,
+ &int_green_Z, &int_blue_X, &int_blue_Y,
+ &int_blue_Z)
+
+ {white,red,green,blue}_{x,y}
+ A color space encoding specified using the
+ chromaticities of the end points and the
+ white point. (PNG_INFO_cHRM)
+
+ {red,green,blue}_{X,Y,Z}
+ A color space encoding specified using the
+ encoding end points - the CIE tristimulus
+ specification of the intended color of the red,
+ green and blue channels in the PNG RGB data.
+ The white point is simply the sum of the three
+ end points. (PNG_INFO_cHRM)
png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
- srgb_intent - the rendering intent (PNG_INFO_sRGB)
+
+ file_srgb_intent - the rendering intent (PNG_INFO_sRGB)
The presence of the sRGB chunk
means that the pixel data is in the
sRGB color space. This chunk also
png_get_iCCP(png_ptr, info_ptr, &name,
&compression_type, &profile, &proflen);
- name - The profile name.
- compression - The compression type; always
- PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
- You may give NULL to this argument to
- ignore it.
- profile - International Color Consortium color
- profile data. May contain NULs.
- proflen - length of profile data in bytes.
+
+ name - The profile name.
+
+ compression_type - The compression type; always
+ PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
+ You may give NULL to this argument to
+ ignore it.
+
+ profile - International Color Consortium color
+ profile data. May contain NULs.
+
+ proflen - length of profile data in bytes.
png_get_sBIT(png_ptr, info_ptr, &sig_bit);
+
sig_bit - the number of significant bits for
(PNG_INFO_sBIT) each of the gray,
red, green, and blue channels,
png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
&num_trans, &trans_color);
+
trans_alpha - array of alpha (transparency)
entries for palette (PNG_INFO_tRNS)
+
+ num_trans - number of transparent entries
+ (PNG_INFO_tRNS)
+
trans_color - graylevel or color sample values of
the single transparent color for
non-paletted images (PNG_INFO_tRNS)
- num_trans - number of transparent entries
- (PNG_INFO_tRNS)
png_get_hIST(png_ptr, info_ptr, &hist);
(PNG_INFO_hIST)
+
hist - histogram of palette (array of
png_uint_16)
png_get_tIME(png_ptr, info_ptr, &mod_time);
+
mod_time - time image was last modified
(PNG_VALID_tIME)
png_get_bKGD(png_ptr, info_ptr, &background);
- background - background color (PNG_VALID_bKGD)
+
+ background - background color (of type
+ png_color_16p) (PNG_VALID_bKGD)
valid 16-bit red, green and blue
values, regardless of color_type
num_comments = png_get_text(png_ptr, info_ptr,
&text_ptr, &num_text);
+
num_comments - number of comments
+
text_ptr - array of png_text holding image
comments
+
text_ptr[i].compression - type of compression used
on "text" PNG_TEXT_COMPRESSION_NONE
PNG_TEXT_COMPRESSION_zTXt
PNG_ITXT_COMPRESSION_NONE
PNG_ITXT_COMPRESSION_zTXt
+
text_ptr[i].key - keyword for comment. Must contain
1-79 characters.
+
text_ptr[i].text - text comments for current
keyword. Can be empty.
+
text_ptr[i].text_length - length of text string,
after decompression, 0 for iTXt
+
text_ptr[i].itxt_length - length of itxt string,
after decompression, 0 for tEXt/zTXt
+
text_ptr[i].lang - language of comment (empty
string for unknown).
+
text_ptr[i].lang_key - keyword in UTF-8
(empty string for unknown).
+
Note that the itxt_length, lang, and lang_key
- members of the text_ptr structure only exist
- when the library is built with iTXt chunk support.
+ members of the text_ptr structure only exist when the
+ library is built with iTXt chunk support. Prior to
+ libpng-1.4.0 the library was built by default without
+ iTXt support. Also note that when iTXt is supported,
+ they contain NULL pointers when the "compression"
+ field contains PNG_TEXT_COMPRESSION_NONE or
+ PNG_TEXT_COMPRESSION_zTXt.
num_text - number of comments (same as
num_comments; you can put NULL here
to avoid the duplication)
+
Note while png_set_text() will accept text, language,
and translated keywords that can be NULL pointers, the
structure returned by png_get_text will always contain
num_spalettes = png_get_sPLT(png_ptr, info_ptr,
&palette_ptr);
+
+ num_spalettes - number of sPLT chunks read.
+
palette_ptr - array of palette structures holding
contents of one or more sPLT chunks
read.
- num_spalettes - number of sPLT chunks read.
png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
&unit_type);
+
offset_x - positive offset from the left edge
- of the screen
+ of the screen (can be negative)
+
offset_y - positive offset from the top edge
- of the screen
+ of the screen (can be negative)
+
unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
&unit_type);
+
res_x - pixels/unit physical resolution in
x direction
+
res_y - pixels/unit physical resolution in
x direction
+
unit_type - PNG_RESOLUTION_UNKNOWN,
PNG_RESOLUTION_METER
png_get_sCAL(png_ptr, info_ptr, &unit, &width,
&height)
+
unit - physical scale units (an integer)
+
width - width of a pixel in physical scale units
+
height - height of a pixel in physical scale units
(width and height are doubles)
png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
&height)
+
unit - physical scale units (an integer)
+
width - width of a pixel in physical scale units
+ (expressed as a string)
+
height - height of a pixel in physical scale units
(width and height are strings like "2.54")
num_unknown_chunks = png_get_unknown_chunks(png_ptr,
info_ptr, &unknowns)
+
unknowns - array of png_unknown_chunk
structures holding unknown chunks
+
unknowns[i].name - name of unknown chunk
+
unknowns[i].data - data of unknown chunk
+
unknowns[i].size - size of unknown chunk's data
+
unknowns[i].location - position of chunk in file
The value of "i" corresponds to the order in which the
chunks were read from the PNG file or inserted with the
png_set_unknown_chunks() function.
+ The value of "location" is a bitwise "or" of
+
+ PNG_HAVE_IHDR (0x01)
+ PNG_HAVE_PLTE (0x02)
+ PNG_AFTER_IDAT (0x08)
+
The data from the pHYs chunk can be retrieved in several convenient
forms:
res_x = png_get_x_pixels_per_meter(png_ptr,
info_ptr)
+
res_y = png_get_y_pixels_per_meter(png_ptr,
info_ptr)
+
res_x_and_y = png_get_pixels_per_meter(png_ptr,
info_ptr)
+
res_x = png_get_x_pixels_per_inch(png_ptr,
info_ptr)
+
res_y = png_get_y_pixels_per_inch(png_ptr,
info_ptr)
+
res_x_and_y = png_get_pixels_per_inch(png_ptr,
info_ptr)
+
aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
info_ptr)
- (Each of these returns 0 [signifying "unknown"] if
+ Each of these returns 0 [signifying "unknown"] if
the data is not present or if res_x is 0;
- res_x_and_y is 0 if res_x != res_y)
+ res_x_and_y is 0 if res_x != res_y
+
+ Note that because of the way the resolutions are
+ stored internally, the inch conversions won't
+ come out to exactly even number. For example,
+ 72 dpi is stored as 0.28346 pixels/meter, and
+ when this is retrieved it is 71.9988 dpi, so
+ be sure to round the returned value appropriately
+ if you want to display a reasonable-looking result.
The data from the oFFs chunk can be retrieved in several convenient
forms:
x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
+
y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
+
x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
+
y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
- (Each of these returns 0 [signifying "unknown" if both
+ Each of these returns 0 [signifying "unknown" if both
x and y are 0] if the data is not present or if the
- chunk is present but the unit is the pixel)
+ chunk is present but the unit is the pixel. The
+ remark about inexact inch conversions applies here
+ as well, because a value in inches can't always be
+ converted to microns and back without some loss
+ of precision.
-For more information, see the png_info definition in png.h and the
+For more information, see the
PNG specification for chunk contents. Be careful with trusting
rowbytes, as some of the transformations could increase the space
needed to hold a row (expand, filler, gray_to_rgb, etc.).
ways to transform the data will be described in the order that they
should occur. This is important, as some of these change the color
type and/or bit depth of the data, and some others only work on
-certain color types and bit depths. Even though each transformation
-checks to see if it has data that it can do something with, you should
-make sure to only enable a transformation if it will be valid for the
-data. For example, don't swap red and blue on grayscale data.
+certain color types and bit depths.
-The colors used for the background and transparency values should be
-supplied in the same format/depth as the current image data. They
-are stored in the same format/depth as the image data in a bKGD or tRNS
-chunk, so this is what libpng expects for this data. The colors are
-transformed to keep in sync with the image data when an application
-calls the png_read_update_info() routine (see below).
+Transformations you request are ignored if they don't have any meaning for a
+particular input data format. However some transformations can have an effect
+as a result of a previous transformation. If you specify a contradictory set of
+transformations, for example both adding and removing the alpha channel, you
+cannot predict the final result.
+
+The color used for the transparency values should be supplied in the same
+format/depth as the current image data. It is stored in the same format/depth
+as the image data in a tRNS chunk, so this is what libpng expects for this data.
+
+The color used for the background value depends on the need_expand argument as
+described below.
Data will be decoded into the supplied row buffers packed into bytes
unless the library has been told to transform it into another format.
in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
is called to insert filler bytes, either before or after each RGB triplet.
16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
-byte of the color value first, unless png_set_strip_16() is called to
+byte of the color value first, unless png_set_scale_16() is called to
transform it to regular RGB RGB triplets, or png_set_filler() or
png_set_add alpha() is called to insert filler bytes, either before or
after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
-be modified with
-png_set_filler(), png_set_add_alpha(), or png_set_strip_16().
+be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(),
+or png_set_scale_16().
The following code transforms grayscale images of less than 8 to 8 bits,
changes paletted images to RGB, and adds a full alpha channel if there is
if (color_type == PNG_COLOR_TYPE_PALETTE)
png_set_palette_to_rgb(png_ptr);
- if (color_type == PNG_COLOR_TYPE_GRAY &&
- bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
-
if (png_get_valid(png_ptr, info_ptr,
PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
-These three functions are actually aliases for png_set_expand(), added
+ if (color_type == PNG_COLOR_TYPE_GRAY &&
+ bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
+
+The first two functions are actually aliases for png_set_expand(), added
in libpng version 1.0.4, with the function names expanded to improve code
readability. In some future version they may actually do different
things.
As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
added. It expands the sample depth without changing tRNS to alpha.
-As of libpng version 1.4.4, not all possible expansions are supported.
+As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as
+png_set_expand(); however, the resultant channels have 16 bits rather than 8.
+Use this when the output color or gray channels are made linear to avoid fairly
+severe accuracy loss.
+
+ if (bit_depth < 16)
+ png_set_expand_16(png_ptr);
+
+PNG can have files with 16 bits per channel. If you only can handle
+8 bits per channel, this will strip the pixels down to 8-bit.
+
+ if (bit_depth == 16)
+#if PNG_LIBPNG_VER >= 10504
+ png_set_scale_16(png_ptr);
+#else
+ png_set_strip_16(png_ptr);
+#endif
+
+(The more accurate "png_set_scale_16()" API became available in libpng version
+1.5.4).
+
+If you need to process the alpha channel on the image separately from the image
+data (for example if you convert it to a bitmap mask) it is possible to have
+libpng strip the channel leaving just RGB or gray data:
+
+ if (color_type & PNG_COLOR_MASK_ALPHA)
+ png_set_strip_alpha(png_ptr);
+
+If you strip the alpha channel you need to find some other way of dealing with
+the information. If, instead, you want to convert the image to an opaque
+version with no alpha channel use png_set_background; see below.
+
+As of libpng version 1.5.2, almost all useful expansions are supported, the
+major ommissions are conversion of grayscale to indexed images (which can be
+done trivially in the application) and conversion of indexed to grayscale (which
+can be done by a trivial manipulation of the palette.)
In the following table, the 01 means grayscale with depth<8, 31 means
indexed with depth<8, other numerals represent the color type, "T" means
the tRNS chunk is present, A means an alpha channel is present, and O
means tRNS or alpha is present but all pixels in the image are opaque.
- FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
+ FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
TO
- 01 -
- 31 -
- 0 1 -
- 0T -
- 0O -
- 2 GX -
- 2T -
- 2O -
- 3 1 -
- 3T -
- 3O -
- 4A T -
- 4O -
- 6A GX TX TX -
- 6O GX TX -
+ 01 - [G] - - - - - - - - - - - - -
+ 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q
+ 0 1 G + . . G G G G G G B B GB GB
+ 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt
+ 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt
+ 2 C P C C C + . . C - - CB CB B B
+ 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt
+ 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt
+ 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q
+ 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt
+ 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt
+ 4A lA G A T T GA GT GT GA GT GT + BA G GBA
+ 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G
+ 6A CA PA CA C C A T tT PA P P C CBA + BA
+ 6O CA PBA CA C C A tT T PA P P CBA C BA +
Within the matrix,
+ "+" identifies entries where 'from' and 'to' are the same.
"-" means the transformation is not supported.
+ "." means nothing is necessary (a tRNS chunk can just be ignored).
+ "t" means the transformation is obtained by png_set_tRNS.
+ "A" means the transformation is obtained by png_set_add_alpha().
"X" means the transformation is obtained by png_set_expand().
"1" means the transformation is obtained by
- png_set_expand_gray_1_2_4_to_8
- "G" means the transformation is obtained by
- png_set_gray_to_rgb().
+ png_set_expand_gray_1_2_4_to_8() (and by png_set_expand()
+ if there is no transparency in the original or the final
+ format).
+ "C" means the transformation is obtained by png_set_gray_to_rgb().
+ "G" means the transformation is obtained by png_set_rgb_to_gray().
"P" means the transformation is obtained by
png_set_expand_palette_to_rgb().
+ "p" means the transformation is obtained by png_set_packing().
+ "Q" means the transformation is obtained by png_set_quantize().
"T" means the transformation is obtained by
png_set_tRNS_to_alpha().
+ "B" means the transformation is obtained by
+ png_set_background(), or png_strip_alpha().
-PNG can have files with 16 bits per channel. If you only can handle
-8 bits per channel, this will strip the pixels down to 8 bit.
-
- if (bit_depth == 16)
- png_set_strip_16(png_ptr);
-
-If, for some reason, you don't need the alpha channel on an image,
-and you want to remove it rather than combining it with the background
-(but the image author certainly had in mind that you *would* combine
-it with the background, so that's what you should probably do):
-
- if (color_type & PNG_COLOR_MASK_ALPHA)
- png_set_strip_alpha(png_ptr);
+When an entry has multiple transforms listed all are required to cause the
+right overall transformation. When two transforms are separated by a comma
+either will do the job. When transforms are enclosed in [] the transform should
+do the job but this is currently unimplemented - a different format will result
+if the suggested transformations are used.
In PNG files, the alpha channel in an image
is the level of opacity. If you need the alpha channel in an image to
values of the pixels:
if (bit_depth < 8)
- png_set_packing(png_ptr);
+ png_set_packing(png_ptr);
PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
stored in a PNG image have been "scaled" or "shifted" up to the next
png_color_8p sig_bit;
if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
- png_set_shift(png_ptr, sig_bit);
+ png_set_shift(png_ptr, sig_bit);
PNG files store 3-color pixels in red, green, blue order. This code
changes the storage of the pixels to blue, green, red:
if (color_type == PNG_COLOR_TYPE_RGB ||
color_type == PNG_COLOR_TYPE_RGB_ALPHA)
- png_set_bgr(png_ptr);
+ png_set_bgr(png_ptr);
PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
into 4 or 8 bytes for windowing systems that need them in this format:
if (color_type == PNG_COLOR_TYPE_RGB)
- png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
+ png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
where "filler" is the 8 or 16-bit number to fill with, and the location is
either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
to do that, you can add a true alpha channel with
if (color_type == PNG_COLOR_TYPE_RGB ||
- color_type == PNG_COLOR_TYPE_GRAY)
- png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
+ color_type == PNG_COLOR_TYPE_GRAY)
+ png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
where "filler" contains the alpha value to assign to each pixel.
This function was added in libpng-1.2.7.
data as ARGB instead of the normal PNG format RGBA:
if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
- png_set_swap_alpha(png_ptr);
+ png_set_swap_alpha(png_ptr);
For some uses, you may want a grayscale image to be represented as
RGB. This code will do that conversion:
if (color_type == PNG_COLOR_TYPE_GRAY ||
color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
- png_set_gray_to_rgb(png_ptr);
+ png_set_gray_to_rgb(png_ptr);
Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
with alpha.
if (color_type == PNG_COLOR_TYPE_RGB ||
color_type == PNG_COLOR_TYPE_RGB_ALPHA)
- png_set_rgb_to_gray_fixed(png_ptr, error_action,
- int red_weight, int green_weight);
+ png_set_rgb_to_gray(png_ptr, error_action,
+ double red_weight, double green_weight);
error_action = 1: silently do the conversion
+
error_action = 2: issue a warning if the original
image has any pixel where
red != green or red != blue
+
error_action = 3: issue an error and abort the
conversion if the original
image has any pixel where
red != green or red != blue
- red_weight: weight of red component times 100000
- green_weight: weight of green component times 100000
+ red_weight: weight of red component
+
+ green_weight: weight of green component
If either weight is negative, default
- weights (21268, 71514) are used.
+ weights are used.
+
+In the corresponding fixed point API the red_weight and green_weight values are
+simply scaled by 100,000:
+
+ png_set_rgb_to_gray(png_ptr, error_action,
+ png_fixed_point red_weight,
+ png_fixed_point green_weight);
If you have set error_action = 1 or 2, you can
later check whether the image really was gray, after processing
the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
It will return a png_byte that is zero if the image was gray or
-1 if there were any non-gray pixels. bKGD and sBIT data
+1 if there were any non-gray pixels. Background and sBIT data
will be silently converted to grayscale, using the green channel
-data, regardless of the error_action setting.
+data for sBIT, regardless of the error_action setting.
-With red_weight+green_weight<=100000,
-the normalized graylevel is computed:
+The default values come from the PNG file cHRM chunk if present; otherwise, the
+defaults correspond to the ITU-R recommendation 709, and also the sRGB color
+space, as recommended in the Charles Poynton's Colour FAQ,
+<http://www.poynton.com/>, in section 9:
- int rw = red_weight * 65536;
- int gw = green_weight * 65536;
- int bw = 65536 - (rw + gw);
- gray = (rw*red + gw*green + bw*blue)/65536;
+ <http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9>
-The default values approximate those recommended in the Charles
-Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
-Copyright (c) 1998-01-04 Charles Poynton <poynton at inforamp.net>
+ Y = 0.2126 * R + 0.7152 * G + 0.0722 * B
- Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
-
-Libpng approximates this with
+Previous versions of this document, 1998 through 2002, recommended a slightly
+different formula:
- Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
+ Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
-which can be expressed with integers as
+Libpng uses an integer approximation:
- Y = (6969 * R + 23434 * G + 2365 * B)/32768
+ Y = (6968 * R + 23434 * G + 2366 * B)/32768
The calculation is done in a linear colorspace, if the image gamma
-is known.
+can be determined.
+
+The png_set_background() function has been described already; it tells libpng to
+composite images with alpha or simple transparency against the supplied
+background color. For compatibility with versions of libpng earlier than
+libpng-1.5.4 it is recommended that you call the function after reading the file
+header, even if you don't want to use the color in a bKGD chunk, if one exists.
-If you have a grayscale and you are using png_set_expand_depth(),
-png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
-a higher bit-depth, you must either supply the background color as a gray
-value at the original file bit-depth (need_expand = 1) or else supply the
-background color as an RGB triplet at the final, expanded bit depth
-(need_expand = 0). Similarly, if you are reading a paletted image, you
-must either supply the background color as a palette index (need_expand = 1)
-or as an RGB triplet that may or may not be in the palette (need_expand = 0).
+If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
+you may use this color, or supply another color more suitable for
+the current display (e.g., the background color from a web page). You
+need to tell libpng how the color is represented, both the format of the
+component values in the color (the number of bits) and the gamma encoding of the
+color. The function takes two arguments, background_gamma_mode and need_expand
+to convey this information; however, only two combinations are likely to be
+useful:
png_color_16 my_background;
png_color_16p image_background;
if (png_get_bKGD(png_ptr, info_ptr, &image_background))
- png_set_background(png_ptr, image_background,
- PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
+ png_set_background(png_ptr, image_background,
+ PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1);
else
- png_set_background(png_ptr, &my_background,
- PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
-
-The png_set_background() function tells libpng to composite images
-with alpha or simple transparency against the supplied background
-color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
-you may use this color, or supply another color more suitable for
-the current display (e.g., the background color from a web page). You
-need to tell libpng whether the color is in the gamma space of the
-display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
-(PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
-that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
-know why anyone would use this, but it's here).
-
-To properly display PNG images on any kind of system, the application needs
-to know what the display gamma is. Ideally, the user will know this, and
-the application will allow them to set it. One method of allowing the user
-to set the display gamma separately for each system is to check for a
-SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
-correctly set.
-
-Note that display_gamma is the overall gamma correction required to produce
-pleasing results, which depends on the lighting conditions in the surrounding
-environment. In a dim or brightly lit room, no compensation other than
-the physical gamma exponent of the monitor is needed, while in a dark room
-a slightly smaller exponent is better.
-
- double gamma, screen_gamma;
-
- if (/* We have a user-defined screen
- gamma value */)
- {
- screen_gamma = user_defined_screen_gamma;
- }
- /* One way that applications can share the same
- screen gamma value */
- else if ((gamma_str = getenv("SCREEN_GAMMA"))
- != NULL)
- {
- screen_gamma = (double)atof(gamma_str);
- }
- /* If we don't have another value */
- else
- {
- screen_gamma = 2.2; /* A good guess for a
- PC monitor in a bright office or a dim room */
- screen_gamma = 2.0; /* A good guess for a
- PC monitor in a dark room */
- screen_gamma = 1.7 or 1.0; /* A good
- guess for Mac systems */
- }
+ png_set_background(png_ptr, &my_background,
+ PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1);
+
+The second call was described above - my_background is in the format of the
+final, display, output produced by libpng. Because you now know the format of
+the PNG it is possible to avoid the need to choose either 8-bit or 16-bit
+output and to retain palette images (the palette colors will be modified
+appropriately and the tRNS chunk removed.) However, if you are doing this,
+take great care not to ask for transformations without checking first that
+they apply!
+
+In the first call the background color has the original bit depth and color type
+of the PNG file. So, for palette images the color is supplied as a palette
+index and for low bit greyscale images the color is a reduced bit value in
+image_background->gray.
+
+If you didn't call png_set_gamma() before reading the file header, for example
+if you need your code to remain compatible with older versions of libpng prior
+to libpng-1.5.4, this is the place to call it.
+
+Do not call it if you called png_set_alpha_mode(); doing so will damage the
+settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is
+supported then you can certainly do png_set_gamma() before reading the PNG
+header.)
+
+This API unconditionally sets the screen and file gamma values, so it will
+override the value in the PNG file unless it is called before the PNG file
+reading starts. For this reason you must always call it with the PNG file
+value when you call it in this position:
+
+ if (png_get_gAMA(png_ptr, info_ptr, &file_gamma))
+ png_set_gamma(png_ptr, screen_gamma, file_gamma);
-The png_set_gamma() function handles gamma transformations of the data.
-Pass both the file gamma and the current screen_gamma. If the file does
-not have a gamma value, you can pass one anyway if you have an idea what
-it is (usually 0.45455 is a good guess for GIF images on PCs). Note
-that file gammas are inverted from screen gammas. See the discussions
-on gamma in the PNG specification for an excellent description of what
-gamma is, and why all applications should support it. It is strongly
-recommended that PNG viewers support gamma correction.
-
- if (png_get_gAMA(png_ptr, info_ptr, &gamma))
- png_set_gamma(png_ptr, screen_gamma, gamma);
else
png_set_gamma(png_ptr, screen_gamma, 0.45455);
If you need to reduce an RGB file to a paletted file, or if a paletted
file has more entries then will fit on your screen, png_set_quantize()
-will do that. Note that this is a simple match dither that merely
+will do that. Note that this is a simple match quantization that merely
finds the closest color available. This should work fairly well with
-optimized palettes, and fairly badly with linear color cubes. If you
-pass a palette that is larger then maximum_colors, the file will
+optimized palettes, but fairly badly with linear color cubes. If you
+pass a palette that is larger than maximum_colors, the file will
reduce the number of colors in the palette so it will fit into
-maximum_colors. If there is a histogram, it will use it to make
+maximum_colors. If there is a histogram, libpng will use it to make
more intelligent choices when reducing the palette. If there is no
histogram, it may not do as good a job.
if (color_type & PNG_COLOR_MASK_COLOR)
{
if (png_get_valid(png_ptr, info_ptr,
- PNG_INFO_PLTE))
+ PNG_INFO_PLTE))
{
png_uint_16p histogram = NULL;
png_get_hIST(png_ptr, info_ptr,
- &histogram);
+ &histogram);
png_set_quantize(png_ptr, palette, num_palette,
max_screen_colors, histogram, 1);
}
+
else
{
png_color std_color_cube[MAX_SCREEN_COLORS] =
This function can also be used to invert grayscale and gray-alpha images:
if (color_type == PNG_COLOR_TYPE_GRAY ||
- color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
+ color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
png_set_invert_mono(png_ptr);
-PNG files store 16 bit pixels in network byte order (big-endian,
+PNG files store 16-bit pixels in network byte order (big-endian,
ie. most significant bits first). This code changes the storage to the
other way (little-endian, i.e. least significant bits first, the
way PCs store them):
if (bit_depth == 16)
- png_set_swap(png_ptr);
+ png_set_swap(png_ptr);
If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
need to change the order the pixels are packed into bytes, you can use:
with
png_set_read_user_transform_fn(png_ptr,
- read_transform_fn);
+ read_transform_fn);
You must supply the function
- void read_transform_fn(png_ptr ptr, row_info_ptr
- row_info, png_bytep data)
+ void read_transform_fn(png_structp png_ptr, png_row_infop
+ row_info, png_bytep data)
See pngtest.c for a working example. Your function will be called
-after all of the other transformations have been processed.
+after all of the other transformations have been processed. Take care with
+interlaced images if you do the interlace yourself - the width of the row is the
+width in 'row_info', not the overall image width.
+
+If supported, libpng provides two information routines that you can use to find
+where you are in processing the image:
+
+ png_get_current_pass_number(png_structp png_ptr);
+ png_get_current_row_number(png_structp png_ptr);
+
+Don't try using these outside a transform callback - firstly they are only
+supported if user transforms are supported, secondly they may well return
+unexpected results unless the row is actually being processed at the moment they
+are called.
+
+With interlaced
+images the value returned is the row in the input sub-image image. Use
+PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
+find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
+
+The discussion of interlace handling above contains more information on how to
+use these values.
You can also set up a pointer to a user structure for use by your
callback function, and you can inform libpng that your transform
function
png_set_user_transform_info(png_ptr, user_ptr,
- user_depth, user_channels);
+ user_depth, user_channels);
The user's application, not libpng, is responsible for allocating and
freeing any memory required for the user structure.
png_get_user_transform_ptr(). For example:
voidp read_user_transform_ptr =
- png_get_user_transform_ptr(png_ptr);
+ png_get_user_transform_ptr(png_ptr);
The last thing to handle is interlacing; this is covered in detail below,
but you must call the function here if you want libpng to handle expansion
After setting the transformations, libpng can update your png_info
structure to reflect any transformations you've requested with this
-call. This is most useful to update the info structure's rowbytes
-field so you can use it to allocate your image memory. This function
-will also update your palette with the correct screen_gamma and
-background if these have been given with the calls above.
+call.
png_read_update_info(png_ptr, info_ptr);
+This is most useful to update the info structure's rowbytes
+field so you can use it to allocate your image memory. This function
+will also update your palette with the correct screen_gamma and
+background if these have been given with the calls above. You may
+only call png_read_update_info() once with a particular info_ptr.
+
After you call png_read_update_info(), you can allocate any
memory you need to hold the image. The row data is simply
raw byte data for all forms of images. As the actual allocation
array of pointers to each row, as it will be needed for some
of the functions below.
+Remember: Before you call png_read_update_info(), the png_get_*()
+functions return the values corresponding to the original PNG image.
+After you call png_read_update_info the values refer to the image
+that libpng will output. Consequently you must call all the png_set_
+functions before you call png_read_update_info(). This is particularly
+important for png_set_interlace_handling() - if you are going to call
+png_read_update_info() you must call png_set_interlace_handling() before
+it unless you want to receive interlaced output.
+
.SS Reading image data
After you've allocated memory, you can read the image data.
and put it in the memory area supplied. You will need to pass in
an array of pointers to each row.
-This function automatically handles interlacing, so you don't need
-to call png_set_interlace_handling() or call this function multiple
-times, or any of that other stuff necessary with png_read_rows().
+This function automatically handles interlacing, so you don't
+need to call png_set_interlace_handling() (unless you call
+png_read_update_info()) or call this function multiple times, or any
+of that other stuff necessary with png_read_rows().
png_read_image(png_ptr, row_pointers);
interlace_type == PNG_INTERLACE_NONE), this is simple:
png_read_rows(png_ptr, row_pointers, NULL,
- number_of_rows);
+ number_of_rows);
where row_pointers is the same as in the png_read_image() call.
If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
get somewhat harder. The only current (PNG Specification version 1.2)
-interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
-is a somewhat complicated 2D interlace scheme, known as Adam7, that
+interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7);
+a somewhat complicated 2D interlace scheme, known as Adam7, that
breaks down an image into seven smaller images of varying size, based
-on an 8x8 grid.
+on an 8x8 grid. This number is defined (from libpng 1.5) as
+PNG_INTERLACE_ADAM7_PASSES in png.h
libpng can fill out those images or it can give them to you "as is".
-If you want them filled out, there are two ways to do that. The one
+It is almost always better to have libpng handle the interlacing for you.
+If you want the images filled out, there are two ways to do that. The one
mentioned in the PNG specification is to expand each pixel to cover
those pixels that have not been read yet (the "rectangle" method).
This results in a blocky image for the first pass, which gradually
before the start of the read. The first method usually looks better,
but tends to be slower, as there are more pixels to put in the rows.
-If you don't want libpng to handle the interlacing details, just call
-png_read_rows() seven times to read in all seven images. Each of the
-images is a valid image by itself, or they can all be combined on an
-8x8 grid to form a single image (although if you intend to combine them
-you would be far better off using the libpng interlace handling).
-
-The first pass will return an image 1/8 as wide as the entire image
-(every 8th column starting in column 0) and 1/8 as high as the original
-(every 8th row starting in row 0), the second will be 1/8 as wide
-(starting in column 4) and 1/8 as high (also starting in row 0). The
-third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
-1/8 as high (every 8th row starting in row 4), and the fourth pass will
-be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
-and every 4th row starting in row 0). The fifth pass will return an
-image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
-while the sixth pass will be 1/2 as wide and 1/2 as high as the original
-(starting in column 1 and row 0). The seventh and final pass will be as
-wide as the original, and 1/2 as high, containing all of the odd
-numbered scanlines. Phew!
-
-If you want libpng to expand the images, call this before calling
-png_start_read_image() or png_read_update_info():
+If, as is likely, you want libpng to expand the images, call this before
+calling png_start_read_image() or png_read_update_info():
if (interlace_type == PNG_INTERLACE_ADAM7)
- number_of_passes
+ number_of_passes
= png_set_interlace_handling(png_ptr);
-This will return the number of passes needed. Currently, this
-is seven, but may change if another interlace type is added.
-This function can be called even if the file is not interlaced,
-where it will return one pass.
+This will return the number of passes needed. Currently, this is seven,
+but may change if another interlace type is added. This function can be
+called even if the file is not interlaced, where it will return one pass.
+You then need to read the whole image 'number_of_passes' times. Each time
+will distribute the pixels from the current pass to the correct place in
+the output image, so you need to supply the same rows to png_read_rows in
+each pass.
If you are not going to display the image after each pass, but are
going to wait until the entire image is read in, use the sparkle
pass, and assumes the data from previous passes is still valid.
png_read_rows(png_ptr, row_pointers, NULL,
- number_of_rows);
+ number_of_rows);
If you only want the first effect (the rectangles), do the same as
before except pass the row buffer in the third parameter, and leave
the second parameter NULL.
png_read_rows(png_ptr, NULL, row_pointers,
- number_of_rows);
+ number_of_rows);
+
+If you don't want libpng to handle the interlacing details, just call
+png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.
+Each of the images is a valid image by itself; however, you will almost
+certainly need to distribute the pixels from each sub-image to the
+correct place. This is where everything gets very tricky.
+
+If you want to retrieve the separate images you must pass the correct
+number of rows to each successive call of png_read_rows(). The calculation
+gets pretty complicated for small images, where some sub-images may
+not even exist because either their width or height ends up zero.
+libpng provides two macros to help you in 1.5 and later versions:
+
+ png_uint_32 width = PNG_PASS_COLS(image_width, pass_number);
+ png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number);
+
+Respectively these tell you the width and height of the sub-image
+corresponding to the numbered pass. 'pass' is in in the range 0 to 6 -
+this can be confusing because the specification refers to the same passes
+as 1 to 7! Be careful, you must check both the width and height before
+calling png_read_rows() and not call it for that pass if either is zero.
+
+You can, of course, read each sub-image row by row. If you want to
+produce optimal code to make a pixel-by-pixel transformation of an
+interlaced image this is the best approach; read each row of each pass,
+transform it, and write it out to a new interlaced image.
+
+If you want to de-interlace the image yourself libpng provides further
+macros to help that tell you where to place the pixels in the output image.
+Because the interlacing scheme is rectangular - sub-image pixels are always
+arranged on a rectangular grid - all you need to know for each pass is the
+starting column and row in the output image of the first pixel plus the
+spacing between each pixel. As of libpng 1.5 there are four macros to
+retrieve this information:
+
+ png_uint_32 x = PNG_PASS_START_COL(pass);
+ png_uint_32 y = PNG_PASS_START_ROW(pass);
+ png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass);
+ png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass);
+
+These allow you to write the obvious loop:
+
+ png_uint_32 input_y = 0;
+ png_uint_32 output_y = PNG_PASS_START_ROW(pass);
+
+ while (output_y < output_image_height)
+ {
+ png_uint_32 input_x = 0;
+ png_uint_32 output_x = PNG_PASS_START_COL(pass);
+
+ while (output_x < output_image_width)
+ {
+ image[output_y][output_x] =
+ subimage[pass][input_y][input_x++];
+
+ output_x += xStep;
+ }
+
+ ++input_y;
+ output_y += yStep;
+ }
+
+Notice that the steps between successive output rows and columns are
+returned as shifts. This is possible because the pixels in the subimages
+are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original
+image. In practice you may need to directly calculate the output coordinate
+given an input coordinate. libpng provides two further macros for this
+purpose:
+
+ png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass);
+ png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass);
+
+Finally a pair of macros are provided to tell you if a particular image
+row or column appears in a given pass:
+
+ int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass);
+ int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass);
+
+Bear in mind that you will probably also need to check the width and height
+of the pass in addition to the above to be sure the pass even exists!
+
+With any luck you are convinced by now that you don't want to do your own
+interlace handling. In reality normally the only good reason for doing this
+is if you are processing PNG files on a pixel-by-pixel basis and don't want
+to load the whole file into memory when it is interlaced.
+
+libpng includes a test program, pngvalid, that illustrates reading and
+writing of interlaced images. If you can't get interlacing to work in your
+code and don't want to leave it to libpng (the recommended approach), see
+how pngvalid.c does it.
.SS Finishing a sequential read
interested in comments or time, which may be stored either before or
after the image data, you should pass the separate png_info struct if
you want to keep the comments from before and after the image
-separate. If you are not interested, you can pass NULL.
+separate.
+
+ png_infop end_info = png_create_info_struct(png_ptr);
+
+ if (!end_info)
+ {
+ png_destroy_read_struct(&png_ptr, &info_ptr,
+ (png_infopp)NULL);
+ return (ERROR);
+ }
png_read_end(png_ptr, end_info);
+If you are not interested, you should still call png_read_end()
+but you can pass NULL, avoiding the need to create an end_info structure.
+
+ png_read_end(png_ptr, (png_infop)NULL);
+
+If you don't call png_read_end(), then your file pointer will be
+left pointing to the first chunk after the last IDAT, which is probably
+not what you want if you expect to read something beyond the end of
+the PNG datastream.
+
When you are done, you can free all memory allocated by libpng like this:
png_destroy_read_struct(&png_ptr, &info_ptr,
&end_info);
+or, if you didn't create an end_info structure,
+
+ png_destroy_read_struct(&png_ptr, &info_ptr,
+ (png_infopp)NULL);
+
It is also possible to individually free the info_ptr members that
point to libpng-allocated storage with the following function:
png_free_data(png_ptr, info_ptr, mask, seq)
+
mask - identifies data to be freed, a mask
containing the bitwise OR of one or
more of
PNG_FREE_SCAL, PNG_FREE_SPLT,
PNG_FREE_TEXT, PNG_FREE_UNKN,
or simply PNG_FREE_ALL
+
seq - sequence number of item to be freed
(-1 for all items)
The default behavior is only to free data that was allocated internally
by libpng. This can be changed, so that libpng will not free the data,
or so that it will free data that was allocated by the user with png_malloc()
-or png_zalloc() and passed in via a png_set_*() function, with
+or png_calloc() and passed in via a png_set_*() function, with
png_data_freer(png_ptr, info_ptr, freer, mask)
- mask - which data elements are affected
- same choices as in png_free_data()
+
freer - one of
PNG_DESTROY_WILL_FREE_DATA
PNG_SET_WILL_FREE_DATA
PNG_USER_WILL_FREE_DATA
+ mask - which data elements are affected
+ same choices as in png_free_data()
+
This function only affects data that has already been allocated.
You can call this function after reading the PNG data but before calling
any png_set_*() functions, to control whether the user or the png_set_*()
responsibility for libpng-allocated data, the application must use
png_free() to free it, and when the user transfers responsibility to libpng
for data that the user has allocated, the user must have used png_malloc()
-or png_zalloc() to allocate it.
+or png_calloc() to allocate it.
If you allocated your row_pointers in a single block, as suggested above in
the description of the high level read interface, you must not transfer
your application instead of by libpng, you can use
png_set_invalid(png_ptr, info_ptr, mask);
+
mask - identifies the chunks to be made invalid,
containing the bitwise OR of one or
more of
png_ptr = png_create_read_struct
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
user_error_fn, user_warning_fn);
+
if (!png_ptr)
return (ERROR);
+
info_ptr = png_create_info_struct(png_ptr);
+
if (!info_ptr)
{
- png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
- (png_infopp)NULL);
- return (ERROR);
+ png_destroy_read_struct(&png_ptr,
+ (png_infopp)NULL, (png_infopp)NULL);
+ return (ERROR);
}
if (setjmp(png_jmpbuf(png_ptr)))
{
- png_destroy_read_struct(&png_ptr, &info_ptr,
- (png_infopp)NULL);
- return (ERROR);
+ png_destroy_read_struct(&png_ptr, &info_ptr,
+ (png_infopp)NULL);
+ return (ERROR);
}
/* This one's new. You can provide functions
{
if (setjmp(png_jmpbuf(png_ptr)))
{
- png_destroy_read_struct(&png_ptr, &info_ptr,
+ png_destroy_read_struct(&png_ptr, &info_ptr,
(png_infopp)NULL);
- return (ERROR);
+ return (ERROR);
}
/* This one's new also. Simply give it a chunk
so there.
*/
png_process_data(png_ptr, info_ptr, buffer, length);
+
+ /* At this point you can call png_process_data_skip if
+ you want to handle data the library will skip yourself;
+ it simply returns the number of bytes to skip (and stops
+ libpng skipping that number of bytes on the next
+ png_process_data call).
return 0;
}
any). You may start getting rows before
png_process_data() returns, so this is your
last chance to prepare for that.
+
+ This is where you turn on interlace handling,
+ assuming you don't want to do it yourself.
+
+ If you need to you can stop the processing of
+ your original input data at this point by calling
+ png_process_data_pause. This returns the number
+ of unprocessed bytes from the last png_process_data
+ call - it is up to you to ensure that the next call
+ sees these bytes again. If you don't want to bother
+ with this you can get libpng to cache the unread
+ bytes by setting the 'save' parameter (see png.h) but
+ then libpng will have to copy the data internally.
*/
}
supplying them because it may make your life
easier.
- For the non-NULL rows of interlaced images,
+ If you did not turn on interlace handling then
+ the callback is called for each row of each
+ sub-image when the image is interlaced. In this
+ case 'row_num' is the row in the sub-image, not
+ the row in the output image as it is in all other
+ cases.
+
+ For the non-NULL rows of interlaced images when
+ you have switched on libpng interlace handling,
you must call png_progressive_combine_row()
passing in the row and the old row. You can
call this function for NULL rows (it will just
return) and for non-interlaced images (it just
does the memcpy for you) if it will make the
code easier. Thus, you can just do this for
- all cases:
+ all cases if you switch on interlace handling;
*/
png_progressive_combine_row(png_ptr, old_row,
for interlaced images), you will have to pass
the current row, and the function will combine
the old row and the new row.
+
+ You can also call png_process_data_pause in this
+ callback - see above.
*/
}
custom writing functions. See the discussion under Customizing libpng.
FILE *fp = fopen(file_name, "wb");
+
if (!fp)
- {
return (ERROR);
- }
Next, png_struct and png_info need to be allocated and initialized.
As these can be both relatively large, you may not want to store these
png_structp png_ptr = png_create_write_struct
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
user_error_fn, user_warning_fn);
+
if (!png_ptr)
return (ERROR);
if (!info_ptr)
{
png_destroy_write_struct(&png_ptr,
- (png_infopp)NULL);
+ (png_infopp)NULL);
return (ERROR);
}
if (setjmp(png_jmpbuf(png_ptr)))
{
- png_destroy_write_struct(&png_ptr, &info_ptr);
+ png_destroy_write_struct(&png_ptr, &info_ptr);
fclose(fp);
return (ERROR);
}
more useful than abort(), as long as your function does not
return.
+Checking for invalid palette index on write was added at libpng
+1.5.10. If a pixel contains an invalid (out-of-range) index libpng issues
+a benign error. This is enabled by default because this condition is an
+error according to the PNG specification, Clause 11.3.2, but the error can
+be ignored in each png_ptr with
+
+ png_set_check_for_invalid_index(png_ptr, 0);
+
+If the error is ignored, or if png_benign_error() treats it as a warning,
+any invalid pixels are written as-is by the encoder, resulting in an
+invalid PNG datastream as output. In this case the application is
+responsible for ensuring that the pixel indexes are in range when it writes
+a PLTE chunk with fewer entries than the bit depth would allow.
+
Now you need to set up the output code. The default for libpng is to
use the C function fwrite(). If you use this, you will need to pass a
valid FILE * in the function png_init_io(). Be sure that the file is
a progress meter or the like. It's demonstrated in pngtest.c.
You must supply a function
- void write_row_callback(png_ptr, png_uint_32 row,
+ void write_row_callback(png_structp png_ptr, png_uint_32 row,
int pass);
{
/* put your code here */
png_set_write_status_fn(png_ptr, write_row_callback);
+When this function is called the row has already been completely processed and
+it has also been written out. The 'row' and 'pass' refer to the next row to be
+handled. For the
+non-interlaced case the row that was just handled is simply one less than the
+passed in row number, and pass will always be 0. For the interlaced case the
+same applies unless the row value is 0, in which case the row just handled was
+the last one from one of the preceding passes. Because interlacing may skip a
+pass you cannot be sure that the preceding pass is just 'pass-1', if you really
+need to know what the last pass is record (row,pass) from the callback and use
+the last recorded value each time.
+
+As with the user transform you can find the output row using the
+PNG_ROW_FROM_PASS_ROW macro.
+
You now have the option of modifying how the compression library will
run. The following functions are mainly for testing, but may be useful
in some cases, like if you need to write PNG files extremely fast and
/* turn on or off filtering, and/or choose
specific filters. You can use either a single
PNG_FILTER_VALUE_NAME or the bitwise OR of one
- or more PNG_FILTER_NAME masks. */
+ or more PNG_FILTER_NAME masks.
+ */
png_set_filter(png_ptr, 0,
PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
PNG_ALL_FILTERS);
-If an application
-wants to start and stop using particular filters during compression,
-it should start out with all of the filters (to ensure that the previous
-row of pixels will be stored in case it's needed later), and then add
-and remove them after the start of compression.
+If an application wants to start and stop using particular filters during
+compression, it should start out with all of the filters (to ensure that
+the previous row of pixels will be stored in case it's needed later),
+and then add and remove them after the start of compression.
If you are writing a PNG datastream that is to be embedded in a MNG
datastream, the second parameter can be either 0 or 64.
data. See the Compression Library (zlib.h and algorithm.txt, distributed
with zlib) for details on the compression levels.
- /* set the zlib compression level */
+ #include zlib.h
+
+ /* Set the zlib compression level */
png_set_compression_level(png_ptr,
Z_BEST_COMPRESSION);
- /* set other zlib parameters */
+ /* Set other zlib parameters for compressing IDAT */
png_set_compression_mem_level(png_ptr, 8);
png_set_compression_strategy(png_ptr,
Z_DEFAULT_STRATEGY);
png_set_compression_method(png_ptr, 8);
png_set_compression_buffer_size(png_ptr, 8192)
-extern PNG_EXPORT(void,png_set_zbuf_size)
+ /* Set zlib parameters for text compression
+ * If you don't call these, the parameters
+ * fall back on those defined for IDAT chunks
+ */
+ png_set_text_compression_mem_level(png_ptr, 8);
+ png_set_text_compression_strategy(png_ptr,
+ Z_DEFAULT_STRATEGY);
+ png_set_text_compression_window_bits(png_ptr, 15);
+ png_set_text_compression_method(png_ptr, 8);
.SS Setting the contents of info for output
png_set_IHDR(png_ptr, info_ptr, width, height,
bit_depth, color_type, interlace_type,
compression_type, filter_method)
+
width - holds the width of the image
in pixels (up to 2^31).
+
height - holds the height of the image
in pixels (up to 2^31).
+
bit_depth - holds the bit depth of one of the
image channels.
(valid values are 1, 2, 4, 8, 16
and depend also on the
color_type. See also significant
bits (sBIT) below).
+
color_type - describes which color/alpha
channels are present.
PNG_COLOR_TYPE_GRAY
interlace_type - PNG_INTERLACE_NONE or
PNG_INTERLACE_ADAM7
+
compression_type - (must be
PNG_COMPRESSION_TYPE_DEFAULT)
+
filter_method - (must be PNG_FILTER_TYPE_DEFAULT
or, if you are writing a PNG to
be embedded in a MNG datastream,
png_set_PLTE(png_ptr, info_ptr, palette,
num_palette);
+
palette - the palette for the file
(array of png_color)
num_palette - number of entries in the palette
- png_set_gAMA(png_ptr, info_ptr, gamma);
- gamma - the gamma the image was created
- at (PNG_INFO_gAMA)
+ png_set_gAMA(png_ptr, info_ptr, file_gamma);
+ png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma);
+
+ file_gamma - the gamma at which the image was
+ created (PNG_INFO_gAMA)
+
+ int_file_gamma - 100,000 times the gamma at which
+ the image was created
+
+ png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y,
+ green_x, green_y, blue_x, blue_y)
+ png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X,
+ green_Y, green_Z, blue_X, blue_Y, blue_Z)
+ png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y,
+ int_red_x, int_red_y, int_green_x, int_green_y,
+ int_blue_x, int_blue_y)
+ png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y,
+ int_red_Z, int_green_X, int_green_Y, int_green_Z,
+ int_blue_X, int_blue_Y, int_blue_Z)
+
+ {white,red,green,blue}_{x,y}
+ A color space encoding specified using the chromaticities
+ of the end points and the white point.
+
+ {red,green,blue}_{X,Y,Z}
+ A color space encoding specified using the encoding end
+ points - the CIE tristimulus specification of the intended
+ color of the red, green and blue channels in the PNG RGB
+ data. The white point is simply the sum of the three end
+ points.
png_set_sRGB(png_ptr, info_ptr, srgb_intent);
+
srgb_intent - the rendering intent
(PNG_INFO_sRGB) The presence of
the sRGB chunk means that the pixel
png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
srgb_intent);
+
srgb_intent - the rendering intent
(PNG_INFO_sRGB) The presence of the
sRGB chunk means that the pixel
written.
png_set_iCCP(png_ptr, info_ptr, name, compression_type,
- profile, proflen);
- name - The profile name.
- compression - The compression type; always
- PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
- You may give NULL to this argument to
- ignore it.
- profile - International Color Consortium color
- profile data. May contain NULs.
- proflen - length of profile data in bytes.
+ profile, proflen);
+
+ name - The profile name.
+
+ compression_type - The compression type; always
+ PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
+ You may give NULL to this argument to
+ ignore it.
+
+ profile - International Color Consortium color
+ profile data. May contain NULs.
+
+ proflen - length of profile data in bytes.
png_set_sBIT(png_ptr, info_ptr, sig_bit);
+
sig_bit - the number of significant bits for
(PNG_INFO_sBIT) each of the gray, red,
green, and blue channels, whichever are
png_set_tRNS(png_ptr, info_ptr, trans_alpha,
num_trans, trans_color);
+
trans_alpha - array of alpha (transparency)
entries for palette (PNG_INFO_tRNS)
+
+ num_trans - number of transparent entries
+ (PNG_INFO_tRNS)
+
trans_color - graylevel or color sample values
(in order red, green, blue) of the
single transparent color for
non-paletted images (PNG_INFO_tRNS)
- num_trans - number of transparent entries
- (PNG_INFO_tRNS)
png_set_hIST(png_ptr, info_ptr, hist);
- (PNG_INFO_hIST)
+
hist - histogram of palette (array of
- png_uint_16)
+ png_uint_16) (PNG_INFO_hIST)
png_set_tIME(png_ptr, info_ptr, mod_time);
+
mod_time - time image was last modified
(PNG_VALID_tIME)
png_set_bKGD(png_ptr, info_ptr, background);
- background - background color (PNG_VALID_bKGD)
+
+ background - background color (of type
+ png_color_16p) (PNG_VALID_bKGD)
png_set_text(png_ptr, info_ptr, text_ptr, num_text);
+
text_ptr - array of png_text holding image
comments
+
text_ptr[i].compression - type of compression used
on "text" PNG_TEXT_COMPRESSION_NONE
PNG_TEXT_COMPRESSION_zTXt
empty for unknown).
text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
or empty for unknown).
+
Note that the itxt_length, lang, and lang_key
- members of the text_ptr structure only exist
- when the library is built with iTXt chunk support.
+ members of the text_ptr structure only exist when the
+ library is built with iTXt chunk support. Prior to
+ libpng-1.4.0 the library was built by default without
+ iTXt support. Also note that when iTXt is supported,
+ they contain NULL pointers when the "compression"
+ field contains PNG_TEXT_COMPRESSION_NONE or
+ PNG_TEXT_COMPRESSION_zTXt.
num_text - number of comments
png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
num_spalettes);
+
palette_ptr - array of png_sPLT_struct structures
to be added to the list of palettes
in the info structure.
png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
unit_type);
+
offset_x - positive offset from the left
edge of the screen
+
offset_y - positive offset from the top
edge of the screen
+
unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
unit_type);
+
res_x - pixels/unit physical resolution
in x direction
+
res_y - pixels/unit physical resolution
in y direction
+
unit_type - PNG_RESOLUTION_UNKNOWN,
PNG_RESOLUTION_METER
png_set_sCAL(png_ptr, info_ptr, unit, width, height)
+
unit - physical scale units (an integer)
+
width - width of a pixel in physical scale units
+
height - height of a pixel in physical scale units
(width and height are doubles)
png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
+
unit - physical scale units (an integer)
+
width - width of a pixel in physical scale units
+ expressed as a string
+
height - height of a pixel in physical scale units
(width and height are strings like "2.54")
png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
num_unknowns)
+
unknowns - array of png_unknown_chunk
structures holding unknown chunks
unknowns[i].name - name of unknown chunk
specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
any language code or translated keyword will not be written out.
-Until text gets around 1000 bytes, it is not worth compressing it.
+Until text gets around a few hundred bytes, it is not worth compressing it.
After the text has been written out to the file, the compression type
is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
so that it isn't written out again at the end (in case you are calling
-png_write_end() with the same struct.
+png_write_end() with the same struct).
The keywords that are given in the PNG Specification are:
Title Short (one line) title or
caption for image
+
Author Name of image's creator
+
Description Description of image (possibly long)
+
Copyright Copyright notice
+
Creation Time Time of original image creation
(usually RFC 1123 format, see below)
+
Software Software used to create the image
+
Disclaimer Legal disclaimer
+
Warning Warning of nature of content
+
Source Device used to create the image
+
Comment Miscellaneous comment; conversion
from other image format
although this isn't a requirement. Unlike the tIME chunk, the
"Creation Time" tEXt chunk is not expected to be automatically changed
by the software. To facilitate the use of RFC 1123 dates, a function
-png_convert_to_rfc1123(png_timep) is provided to convert from PNG
-time to an RFC 1123 format string.
+png_convert_to_rfc1123_buffer(png_ptr, buffer, png_timep) is provided to
+convert from PNG time to an RFC 1123 format string. The caller must provide
+a writeable buffer of at least 29 bytes.
.SS Writing unknown chunks
/* Set the true bit depth of the image data */
if (color_type & PNG_COLOR_MASK_COLOR)
{
- sig_bit.red = true_bit_depth;
- sig_bit.green = true_bit_depth;
- sig_bit.blue = true_bit_depth;
+ sig_bit.red = true_bit_depth;
+ sig_bit.green = true_bit_depth;
+ sig_bit.blue = true_bit_depth;
}
+
else
{
- sig_bit.gray = true_bit_depth;
+ sig_bit.gray = true_bit_depth;
}
+
if (color_type & PNG_COLOR_MASK_ALPHA)
{
- sig_bit.alpha = true_bit_depth;
+ sig_bit.alpha = true_bit_depth;
}
png_set_sBIT(png_ptr, info_ptr, &sig_bit);
png_set_shift(png_ptr, &sig_bit);
-PNG files store 16 bit pixels in network byte order (big-endian,
+PNG files store 16-bit pixels in network byte order (big-endian,
ie. most significant bits first). This code would be used if they are
supplied the other way (little-endian, i.e. least significant bits
first, the way PCs store them):
You must supply the function
- void write_transform_fn(png_ptr ptr, row_info_ptr
+ void write_transform_fn(png_structp png_ptr, png_row_infop
row_info, png_bytep data)
See pngtest.c for a working example. Your function will be called
-before any of the other transformations are processed.
+before any of the other transformations are processed. If supported
+libpng also supplies an information routine that may be called from
+your callback:
+
+ png_get_current_row_number(png_ptr);
+ png_get_current_pass_number(png_ptr);
+
+This returns the current row passed to the transform. With interlaced
+images the value returned is the row in the input sub-image image. Use
+PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
+find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
+
+The discussion of interlace handling above contains more information on how to
+use these values.
You can also set up a pointer to a user structure for use by your
callback function.
If you don't want libpng to handle the interlacing details, just
use png_set_interlace_handling() and call png_write_rows() the
-correct number of times to write all seven sub-images.
+correct number of times to write all the sub-images
+(png_set_interlace_handling() returns the number of sub-images.)
If you want libpng to build the sub-images, call this before you start
writing any rows:
- number_of_passes =
- png_set_interlace_handling(png_ptr);
+ number_of_passes = png_set_interlace_handling(png_ptr);
This will return the number of passes needed. Currently, this is seven,
but may change if another interlace type is added.
Then write the complete image number_of_passes times.
- png_write_rows(png_ptr, row_pointers,
- number_of_rows);
+ png_write_rows(png_ptr, row_pointers, number_of_rows);
+
+Think carefully before you write an interlaced image. Typically code that
+reads such images reads all the image data into memory, uncompressed, before
+doing any processing. Only code that can display an image on the fly can
+take advantage of the interlacing and even then the image has to be exactly
+the correct size for the output device, because scaling an image requires
+adjacent pixels and these are not available until all the passes have been
+read.
+
+If you do write an interlaced image you will hardly ever need to handle
+the interlacing yourself. Call png_set_interlace_handling() and use the
+approach described above.
-As some of these rows are not used, and thus return immediately, you may
-want to read about interlacing in the PNG specification, and only update
-the rows that are actually used.
+The only time it is conceivable that you will really need to write an
+interlaced image pass-by-pass is when you have read one pass by pass and
+made some pixel-by-pixel transformation to it, as described in the read
+code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros
+to determine the size of each sub-image in turn and simply write the rows
+you obtained from the read code.
.SS Finishing a sequential write
point to libpng-allocated storage with the following function:
png_free_data(png_ptr, info_ptr, mask, seq)
+
mask - identifies data to be freed, a mask
containing the bitwise OR of one or
more of
PNG_FREE_SCAL, PNG_FREE_SPLT,
PNG_FREE_TEXT, PNG_FREE_UNKN,
or simply PNG_FREE_ALL
+
seq - sequence number of item to be freed
(-1 for all items)
The default behavior is only to free data that was allocated internally
by libpng. This can be changed, so that libpng will not free the data,
or so that it will free data that was allocated by the user with png_malloc()
-or png_zalloc() and passed in via a png_set_*() function, with
+or png_calloc() and passed in via a png_set_*() function, with
png_data_freer(png_ptr, info_ptr, freer, mask)
- mask - which data elements are affected
- same choices as in png_free_data()
+
freer - one of
PNG_DESTROY_WILL_FREE_DATA
PNG_SET_WILL_FREE_DATA
PNG_USER_WILL_FREE_DATA
+ mask - which data elements are affected
+ same choices as in png_free_data()
+
For example, to transfer responsibility for some data from a read structure
to a write structure, you could use
png_data_freer(read_ptr, read_info_ptr,
PNG_USER_WILL_FREE_DATA,
PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
+
png_data_freer(write_ptr, write_info_ptr,
PNG_DESTROY_WILL_FREE_DATA,
PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
application must use
png_free() to free it, and when the user transfers responsibility to libpng
for data that the user has allocated, the user must have used png_malloc()
-or png_zalloc() to allocate it.
+or png_calloc() to allocate it.
If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
separately, do not transfer responsibility for freeing text_ptr to libpng,
application, your application must not separately free those members.
For a more compact example of writing a PNG image, see the file example.c.
-.SH V. Modifying/Customizing libpng:
+.SH V. Simplified API
+
+The simplified API, which became available in libpng-1.6.0, hides the details
+of both libpng and the PNG file format itself.
+It allows PNG files to be read into a very limited number of
+in-memory bitmap formats or to be written from the same formats. If these
+formats do not accomodate your needs then you can, and should, use the more
+sophisticated APIs above - these support a wide variety of in-memory formats
+and a wide variety of sophisticated transformations to those formats as well
+as a wide variety of APIs to manipulate ancilliary information.
+
+To read a PNG file using the simplified API:
+
+ 1) Declare a 'png_image' structure (see below) on the
+ stack and memset() it to all zero.
+
+ 2) Call the appropriate png_image_begin_read... function.
+
+ 3) Set the png_image 'format' member to the required
+ format and allocate a buffer for the image.
+
+ 4) Call png_image_finish_read to read the image into
+ your buffer.
+
+There are no restrictions on the format of the PNG input itself; all valid
+color types, bit depths, and interlace methods are acceptable, and the
+input image is transformed as necessary to the requested in-memory format
+during the png_image_finish_read() step.
+
+To write a PNG file using the simplified API:
+
+ 1) Declare a 'png_image' structure on the stack and memset()
+ it to all zero.
+
+ 2) Initialize the members of the structure that describe the
+ image, setting the 'format' member to the format of the
+ image in memory.
+
+ 3) Call the appropriate png_image_write... function with a
+ pointer to the image to write the PNG data.
+
+png_image is a structure that describes the in-memory format of an image
+when it is being read or define the in-memory format of an image that you
+need to write. The "png_image" structure contains the following members:
+
+ png_uint_32 version Set to PNG_IMAGE_VERSION
+ png_uint_32 width Image width in pixels (columns)
+ png_uint_32 height Image height in pixels (rows)
+ png_uint_32 format Image format as defined below
+ png_uint_32 flags A bit mask containing informational flags
+ png_controlp opaque Initialize to NULL, free with png_image_free
+ png_uint_32 colormap_entries; Number of entries in the color-map
+ png_uint_32 warning_or_error;
+ char message[64];
+
+In the event of an error or warning the following field warning_or_error
+field will be set to a non-zero value and the 'message' field will contain
+a '\0' terminated string with the libpng error or warning message. If both
+warnings and an error were encountered, only the error is recorded. If there
+are multiple warnings, only the first one is recorded.
+
+The upper 30 bits of this value are reserved; the low two bits contain
+a two bit code such that a value more than 1 indicates a failure in the API
+just called:
+
+ 0 - no warning or error
+ 1 - warning
+ 2 - error
+ 3 - error preceded by warning
+
+The pixels (samples) of the image have one to four channels whose components
+have original values in the range 0 to 1.0:
+
+ 1: A single gray or luminance channel (G).
+ 2: A gray/luminance channel and an alpha channel (GA).
+ 3: Three red, green, blue color channels (RGB).
+ 4: Three color channels and an alpha channel (RGBA).
+
+The channels are encoded in one of two ways:
+
+ a) As a small integer, value 0..255, contained in a single byte. For the
+alpha channel the original value is simply value/255. For the color or
+luminance channels the value is encoded according to the sRGB specification
+and matches the 8-bit format expected by typical display devices.
+
+The color/gray channels are not scaled (pre-multiplied) by the alpha
+channel and are suitable for passing to color management software.
+
+ b) As a value in the range 0..65535, contained in a 2-byte integer. All
+channels can be converted to the original value by dividing by 65535; all
+channels are linear. Color channels use the RGB encoding (RGB end-points) of
+the sRGB specification. This encoding is identified by the
+PNG_FORMAT_FLAG_LINEAR flag below.
+
+When an alpha channel is present it is expected to denote pixel coverage
+of the color or luminance channels and is returned as an associated alpha
+channel: the color/gray channels are scaled (pre-multiplied) by the alpha
+value.
+
+When a color-mapped image is used as a result of calling
+png_image_read_colormap or png_image_write_colormap the channels are encoded
+in the color-map and the descriptions above apply to the color-map entries.
+The image data is encoded as small integers, value 0..255, that index the
+entries in the color-map. One integer (one byte) is stored for each pixel.
+
+PNG_FORMAT_*
+
+The #defines to be used in png_image::format. Each #define identifies a
+particular layout of channel data and, if present, alpha values. There are
+separate defines for each of the two channel encodings.
+
+A format is built up using single bit flag values. Not all combinations are
+valid: use the bit flag values below for testing a format returned by the
+read APIs, but set formats from the derived values.
+
+When reading or writing color-mapped images the format should be set to the
+format of the entries in the color-map then png_image_{read,write}_colormap
+called to read or write the color-map and set the format correctly for the
+image data. Do not set the PNG_FORMAT_FLAG_COLORMAP bit directly!
+
+NOTE: libpng can be built with particular features disabled, if you see
+compiler errors because the definition of one of the following flags has been
+compiled out it is because libpng does not have the required support. It is
+possible, however, for the libpng configuration to enable the format on just
+read or just write; in that case you may see an error at run time. You can
+guard against this by checking for the definition of:
+
+ PNG_SIMPLIFIED_{READ,WRITE}_{BGR,AFIRST}_SUPPORTED
+
+ PNG_FORMAT_FLAG_ALPHA 0x01 format with an alpha channel
+ PNG_FORMAT_FLAG_COLOR 0x02 color format: otherwise grayscale
+ PNG_FORMAT_FLAG_LINEAR 0x04 png_uint_16 channels else png_byte
+ PNG_FORMAT_FLAG_COLORMAP 0x08 libpng use only
+ PNG_FORMAT_FLAG_BGR 0x10 BGR colors, else order is RGB
+ PNG_FORMAT_FLAG_AFIRST 0x20 alpha channel comes first
+
+Supported formats are as follows. Future versions of libpng may support more
+formats; for compatibility with older versions simply check if the format
+macro is defined using #ifdef. These defines describe the in-memory layout
+of the components of the pixels of the image.
+
+First the single byte formats:
+
+ PNG_FORMAT_GRAY 0
+ PNG_FORMAT_GA PNG_FORMAT_FLAG_ALPHA
+ PNG_FORMAT_AG (PNG_FORMAT_GA|PNG_FORMAT_FLAG_AFIRST)
+ PNG_FORMAT_RGB PNG_FORMAT_FLAG_COLOR
+ PNG_FORMAT_BGR (PNG_FORMAT_FLAG_COLOR|PNG_FORMAT_FLAG_BGR)
+ PNG_FORMAT_RGBA (PNG_FORMAT_RGB|PNG_FORMAT_FLAG_ALPHA)
+ PNG_FORMAT_ARGB (PNG_FORMAT_RGBA|PNG_FORMAT_FLAG_AFIRST)
+ PNG_FORMAT_BGRA (PNG_FORMAT_BGR|PNG_FORMAT_FLAG_ALPHA)
+ PNG_FORMAT_ABGR (PNG_FORMAT_BGRA|PNG_FORMAT_FLAG_AFIRST)
+
+Then the linear 2-byte formats. When naming these "Y" is used to
+indicate a luminance (gray) channel. The component order within the pixel
+is always the same - there is no provision for swapping the order of the
+components in the linear format.
+
+ PNG_FORMAT_LINEAR_Y PNG_FORMAT_FLAG_LINEAR
+ PNG_FORMAT_LINEAR_Y_ALPHA
+ (PNG_FORMAT_FLAG_LINEAR|PNG_FORMAT_FLAG_ALPHA)
+ PNG_FORMAT_LINEAR_RGB
+ (PNG_FORMAT_FLAG_LINEAR|PNG_FORMAT_FLAG_COLOR)
+ PNG_FORMAT_LINEAR_RGB_ALPHA
+ (PNG_FORMAT_FLAG_LINEAR|PNG_FORMAT_FLAG_COLOR|
+ PNG_FORMAT_FLAG_ALPHA)
+
+Color-mapped formats are obtained by calling png_image_{read,write}_colormap,
+as appropriate after setting png_image::format to the format of the color-map
+to be read or written. Applications may check the value of
+PNG_FORMAT_FLAG_COLORMAP to see if they have called the colormap API. The
+format of the color-map may be extracted using the following macro.
+
+ PNG_FORMAT_OF_COLORMAP(fmt) ((fmt) & ~PNG_FORMAT_FLAG_COLORMAP)
+
+PNG_IMAGE macros
+
+These are convenience macros to derive information from a png_image
+structure. The PNG_IMAGE_SAMPLE_ macros return values appropriate to the
+actual image sample values - either the entries in the color-map or the
+pixels in the image. The PNG_IMAGE_PIXEL_ macros return corresponding values
+for the pixels and will always return 1 after a call to
+png_image_{read,write}_colormap. The remaining macros return information
+about the rows in the image and the complete image.
+
+NOTE: All the macros that take a png_image::format parameter are compile time
+constants if the format parameter is, itself, a constant. Therefore these
+macros can be used in array declarations and case labels where required.
+Similarly the macros are also pre-processor constants (sizeof is not used) so
+they can be used in #if tests.
+
+First the information about the samples.
+
+ PNG_IMAGE_SAMPLE_CHANNELS(fmt)
+ Returns the total number of channels in a given format: 1..4
+
+ PNG_IMAGE_SAMPLE_COMPONENT_SIZE(fmt)
+ Returns the size in bytes of a single component of a pixel or color-map
+ entry (as appropriate) in the image.
+
+ PNG_IMAGE_SAMPLE_SIZE(fmt)
+ This is the size of the sample data for one sample. If the image is
+ color-mapped it is the size of one color-map entry (and image pixels are
+ one byte in size), otherwise it is the size of one image pixel.
+
+ PNG_IMAGE_COLORMAP_SIZE(fmt)
+ The size of the color-map required by the format; this is the size of the
+ color-map buffer passed to the png_image_{read,write}_colormap APIs, it is
+ a fixed number determined by the format so can easily be allocated on the
+ stack if necessary.
+
+#define PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(fmt)\
+ (PNG_IMAGE_SAMPLE_CHANNELS(fmt) * 256)
+ /* The maximum size of the color-map required by the format expressed in a
+ * count of components. This can be used to compile-time allocate a
+ * color-map:
+ *
+ * png_uint_16 colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(linear_fmt)];
+ *
+ * png_byte colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(sRGB_fmt)];
+ *
+ * Alternatively use the PNG_IMAGE_COLORMAP_SIZE macro below to use the
+ * information from one of the png_image_begin_read_ APIs and dynamically
+ * allocate the required memory.
+ */
+
+
+Corresponding information about the pixels
+
+ PNG_IMAGE_PIXEL_(test,fmt)
+
+ PNG_IMAGE_PIXEL_CHANNELS(fmt)
+ The number of separate channels (components) in a pixel; 1 for a
+ color-mapped image.
+
+ PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt)\
+ The size, in bytes, of each component in a pixel; 1 for a color-mapped
+ image.
+
+ PNG_IMAGE_PIXEL_SIZE(fmt)
+ The size, in bytes, of a complete pixel; 1 for a color-mapped image.
+
+Information about the whole row, or whole image
+
+ PNG_IMAGE_ROW_STRIDE(image)
+ Returns the total number of components in a single row of the image; this
+ is the minimum 'row stride', the minimum count of components between each
+ row. For a color-mapped image this is the minimum number of bytes in a
+ row.
+
+ PNG_IMAGE_BUFFER_SIZE(image, row_stride)
+ Returns the size, in bytes, of an image buffer given a png_image and a row
+ stride - the number of components to leave space for in each row.
+
+ PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB == 0x01
+ This indicates the the RGB values of the in-memory bitmap do not
+ correspond to the red, green and blue end-points defined by sRGB.
+
+ PNG_IMAGE_FLAG_COLORMAP == 0x02
+ The PNG is color-mapped. If this flag is set png_image_read_colormap
+ can be used without further loss of image information. If it is not set
+ png_image_read_colormap will cause significant loss if the image has any
+
+READ APIs
+
+ The png_image passed to the read APIs must have been initialized by setting
+ the png_controlp field 'opaque' to NULL (or, better, memset the whole thing.)
+
+ int png_image_begin_read_from_file( png_imagep image,
+ const char *file_name)
+
+ The named file is opened for read and the image header
+ is filled in from the PNG header in the file.
+
+ int png_image_begin_read_from_stdio (png_imagep image,
+ FILE* file)
+
+ The PNG header is read from the stdio FILE object.
+
+ int png_image_begin_read_from_memory(png_imagep image,
+ png_const_voidp memory, png_size_t size)
+
+ The PNG header is read from the given memory buffer.
+
+ int png_image_finish_read(png_imagep image,
+ png_colorp background, void *buffer,
+ png_int_32 row_stride, void *colormap));
+
+ Finish reading the image into the supplied buffer and
+ clean up the png_image structure.
+
+ row_stride is the step, in png_byte or png_uint_16 units
+ as appropriate, between adjacent rows. A positive stride
+ indicates that the top-most row is first in the buffer -
+ the normal top-down arrangement. A negative stride
+ indicates that the bottom-most row is first in the buffer.
+
+ background need only be supplied if an alpha channel must
+ be removed from a png_byte format and the removal is to be
+ done by compositing on a solid color; otherwise it may be
+ NULL and any composition will be done directly onto the
+ buffer. The value is an sRGB color to use for the
+ background, for grayscale output the green channel is used.
+
+ For linear output removing the alpha channel is always done
+ by compositing on black.
+
+ void png_image_free(png_imagep image)
+
+ Free any data allocated by libpng in image->opaque,
+ setting the pointer to NULL. May be called at any time
+ after the structure is initialized.
+
+When the simplified API needs to convert between sRGB and linear colorspaces,
+the actual sRGB transfer curve defined in the sRGB specification (see the
+article at http://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2
+approximation used elsewhere in libpng.
+
+WRITE APIS
+
+For write you must initialize a png_image structure to describe the image to
+be written:
+
+ version: must be set to PNG_IMAGE_VERSION
+ opaque: must be initialized to NULL
+ width: image width in pixels
+ height: image height in rows
+ format: the format of the data you wish to write
+ flags: set to 0 unless one of the defined flags applies; set
+ PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB for color format images
+ where the RGB values do not correspond to the colors in sRGB.
+ colormap_entries: set to the number of entries in the color-map (0 to 256)
+
+ int png_image_write_to_file, (png_imagep image,
+ const char *file, int convert_to_8bit, const void *buffer,
+ png_int_32 row_stride, const void *colormap));
+
+ Write the image to the named file.
+
+ int png_image_write_to_stdio(png_imagep image, FILE *file,
+ int convert_to_8_bit, const void *buffer,
+ png_int_32 row_stride, const void *colormap)
+
+ Write the image to the given (FILE*).
+
+With all write APIs if image is in one of the linear formats with
+(png_uint_16) data then setting convert_to_8_bit will cause the output to be
+a (png_byte) PNG gamma encoded according to the sRGB specification, otherwise
+a 16-bit linear encoded PNG file is written.
+
+With all APIs row_stride is handled as in the read APIs - it is the spacing
+from one row to the next in component sized units (float) and if negative
+indicates a bottom-up row layout in the buffer.
+
+Note that the write API does not support interlacing, sub-8-bit pixels,
+and indexed (paletted) images.
+
+.SH VI. Modifying/Customizing libpng
There are two issues here. The first is changing how libpng does
standard things like memory allocation, input/output, and error handling.
these functions, call the appropriate png_set_*_fn() function.
Memory allocation is done through the functions png_malloc(), png_calloc(),
-and png_free(). These currently just call the standard C functions.
-png_calloc() calls png_malloc() and then png_memset() to clear the newly
-allocated memory to zero. If your pointers can't access more then 64K
-at a time, you will want to set MAXSEG_64K in zlib.h. Since it is
+and png_free(). The png_malloc() and png_free() functions currently just
+call the standard C functions and png_calloc() calls png_malloc() and then
+clears the newly allocated memory to zero; note that png_calloc(png_ptr, size)
+is not the same as the calloc(number, size) function provided by stdlib.h.
+There is limited support for certain systems with segmented memory
+architectures and the types of pointers declared by png.h match this; you
+will have to use appropriate pointers in your application. Since it is
unlikely that the method of handling memory allocation on a platform
will change between applications, these functions must be modified in
the library at compile time. If you prefer to use a different method
png_voidp malloc_fn(png_structp png_ptr,
png_alloc_size_t size);
+
void free_fn(png_structp png_ptr, png_voidp ptr);
Your malloc_fn() must return NULL in case of failure. The png_malloc()
void user_read_data(png_structp png_ptr,
png_bytep data, png_size_t length);
+
void user_write_data(png_structp png_ptr,
png_bytep data, png_size_t length);
+
void user_flush_data(png_structp png_ptr);
The user_read_data() function is responsible for detecting and
void user_error_fn(png_structp png_ptr,
png_const_charp error_msg);
+
void user_warning_fn(png_structp png_ptr,
png_const_charp warning_msg);
after a longjmp, so the user may want to be careful about doing anything
after setjmp returns non-zero besides returning itself. Consult your
compiler documentation for more details. For an alternative approach, you
-may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net).
+may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net),
+which is illustrated in pngvalid.c and in contrib/visupng.
+
+Beginning in libpng-1.4.0, the png_set_benign_errors() API became available.
+You can use this to handle certain errors (normally handled as errors)
+as warnings.
+
+ png_set_benign_errors (png_ptr, int allowed);
+
+ allowed: 0: (default) treat png_benign_error() an error.
+ 1: treat png_benign_error() as a warning.
.SS Custom chunks
similarly. Second, check out the sections of libpng that read and
write chunks. Try to find a chunk that is similar to yours and use
it as a template. More details can be found in the comments inside
-the code. It is best to handle unknown chunks in a generic method,
-via callback functions, instead of by modifying libpng functions.
+the code. It is best to handle private or unknown chunks in a generic method,
+via callback functions, instead of by modifying libpng functions. This
+is illustrated in pngtest.c, which uses a callback function to handle a
+private "vpAg" chunk and the new "sTER" chunk, which are both unknown to
+libpng.
If you wish to write your own transformation for the data, look through
the part of the code that does the transformations, and check out some of
transformation to the one you want to add and copy off of it. More details
can be found in the comments inside the code itself.
-.SS Configuring for 16 bit platforms
+.SS Configuring for 16-bit platforms
You will want to look into zconf.h to tell zlib (and thus libpng) that
it cannot allocate more then 64K at a time. Even if you can, the memory
all set. Everything in the library (except for zlib's structure) is
expecting far data. You must use the typedefs with the p or pp on
the end for pointers (or at least look at them and be careful). Make
-note that the rows of data are defined as png_bytepp, which is an
-unsigned char far * far *.
+note that the rows of data are defined as png_bytepp, which is
+an "unsigned char far * far *".
.SS Configuring for gui/windowing platforms:
The includes that are not needed outside libpng are placed in pngpriv.h,
which is only used by the routines inside libpng itself.
The files in libpng proper only include pngpriv.h and png.h, which
-in turn includes pngconf.h.
+%14%in turn includes pngconf.h.
+in turn includes pngconf.h and, as of libpng-1.5.0, pnglibconf.h.
+As of libpng-1.5.0, pngpriv.h also includes three other private header
+files, pngstruct.h, pnginfo.h, and pngdebug.h, which contain material
+that previously appeared in the public headers.
.SS Configuring zlib:
files larger than just storing the raw bitmap. You can specify the
compression level by calling:
+ #include zlib.h
png_set_compression_level(png_ptr, level);
Another useful one is to reduce the memory level used by the library.
data being emitted in smaller stored blocks, with a correspondingly
larger relative overhead of up to 15% in the worst case.
+ #include zlib.h
png_set_compression_mem_level(png_ptr, level);
The other functions are for configuring zlib. They are not recommended
for normal use and may result in writing an invalid PNG file. See
zlib.h for more information on what these mean.
+ #include zlib.h
png_set_compression_strategy(png_ptr,
strategy);
+
png_set_compression_window_bits(png_ptr,
window_bits);
+
png_set_compression_method(png_ptr, method);
+
png_set_compression_buffer_size(png_ptr, size);
+As of libpng version 1.5.4, additional APIs became
+available to set these separately for non-IDAT
+compressed chunks such as zTXt, iTXt, and iCCP:
+
+ #include zlib.h
+ #if PNG_LIBPNG_VER >= 10504
+ png_set_text_compression_level(png_ptr, level);
+
+ png_set_text_compression_mem_level(png_ptr, level);
+
+ png_set_text_compression_strategy(png_ptr,
+ strategy);
+
+ png_set_text_compression_window_bits(png_ptr,
+ window_bits);
+
+ png_set_text_compression_method(png_ptr, method);
+ #endif
+
.SS Controlling row filtering
If you want to control whether libpng uses filtering or not, which
you can turn off individual capabilities with defines that begin with
PNG_NO_.
+In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead.
+
You can also turn all of the transforms and ancillary chunk capabilities
off en masse with compiler directives that define
PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
All the reading and writing specific code are in separate files, so the
linker should only grab the files it needs. However, if you want to
make sure, or if you are building a stand alone library, all the
-reading files start with pngr and all the writing files start with
-pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
+reading files start with "pngr" and all the writing files start with "pngw".
+The files that don't match either (like png.c, pngtrans.c, etc.)
are used for both reading and writing, and always need to be included.
The progressive reader is in pngpread.c
is expanded to
- if(PNG_DEBUG > 2)
- fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
+ if (PNG_DEBUG > 2)
+ fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
can still use PNG_DEBUG to control your own debugging:
having level = 0 will be printed. There aren't any such statements in
this version of libpng, but if you insert some they will be printed.
-.SH VI. MNG support
+.SS Prepending a prefix to exported symbols
+
+Starting with libpng-1.6.0, you can configure libpng (when using the
+"configure" script) to prefix all exported symbols by means of the
+configuration option "--with-libpng-prefix=FOO_", where FOO_ can be any
+string beginning with a letter and containing only uppercase
+and lowercase letters, digits, and the underscore (i.e., a C language
+identifier). This creates a set of macros in pnglibconf.h, so this is
+transparent to applications; their function calls get transformed by
+the macros to use the modified names.
+
+.SH VII. MNG support
The MNG specification (available at http://www.libpng.org/pub/mng) allows
certain extensions to PNG for PNG images that are embedded in MNG datastreams.
png_permit_mng_features() function:
feature_set = png_permit_mng_features(png_ptr, mask)
+
mask is a png_uint_32 containing the bitwise OR of the
features you want to enable. These include
PNG_FLAG_MNG_EMPTY_PLTE
PNG_FLAG_MNG_FILTER_64
PNG_ALL_MNG_FEATURES
+
feature_set is a png_uint_32 that is the bitwise AND of
your mask with the set of MNG features that is
supported by the version of libpng that you are using.
them. You may wish to consider using libmng (available at
http://www.libmng.com) instead.
-.SH VII. Changes to Libpng from version 0.88
+.SH VIII. Changes to Libpng from version 0.88
It should be noted that versions of libpng later than 0.96 are not
distributed by the original libpng author, Guy Schalnat, nor by
The old libpng functions png_read_init(), png_write_init(),
png_info_init(), png_read_destroy(), and png_write_destroy() have been
moved to PNG_INTERNAL in version 0.95 to discourage their use. These
-functions will be removed from libpng version 2.0.0.
+functions will be removed from libpng version 1.4.0.
The preferred method of creating and initializing the libpng structures is
via the png_create_read_struct(), png_create_write_struct(), and
version with leading zero, and release number with leading zero,
(e.g., libpng_vn for version 1.0.7 is 10007).
+Note that this function does not take a png_ptr, so you can call it
+before you've created one.
+
You can also check which version of png.h you used when compiling your
application:
png_uint_32 application_vn = PNG_LIBPNG_VER;
-.SH VIII. Changes to Libpng from version 1.0.x to 1.2.x
+.SH IX. Changes to Libpng from version 1.0.x to 1.2.x
Support for user memory management was enabled by default. To
accomplish this, the functions png_create_read_struct_2(),
png_set_expand_gray_1_2_4_to_8()
which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
-.SH IX. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
+.SH X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
Private libpng prototypes and macro definitions were moved from
png.h and pngconf.h into a new pngpriv.h header file.
png_set_asm_flags(), and png_mmx_supported()
We removed the obsolete png_check_sig(), png_memcpy_check(), and
-png_memset_check() functions. Instead use !png_sig_cmp(), png_memcpy(),
-and png_memset(), respectively.
+png_memset_check() functions. Instead use !png_sig_cmp(), memcpy(),
+and memset(), respectively.
The function png_set_gray_1_2_4_to_8() was removed. It has been
deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
png_set_expand_gray_1_2_4_to_8() because the former function also
-expanded palette images.
+expanded any tRNS chunk to an alpha channel.
+
+Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32
+were added and are used by default instead of the corresponding
+functions. Unfortunately,
+from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
+function) incorrectly returned a value of type png_uint_32.
We changed the prototype for png_malloc() from
png_malloc(png_structp png_ptr, png_uint_32 size)
This also applies to the prototype for the user replacement malloc_fn().
The png_calloc() function was added and is used in place of
-of "png_malloc(); png_memset();" except in the case in png_read_png()
+of "png_malloc(); memset();" except in the case in png_read_png()
where the array consists of pointers; in this case a "for" loop is used
after the png_malloc() to set the pointers to NULL, to give robust.
behavior in case the application runs out of memory part-way through
The png_zalloc() and png_zfree() functions are no longer exported.
The png_zalloc() function no longer zeroes out the memory that it
-allocates.
+allocates. Applications that called png_zalloc(png_ptr, number, size)
+can call png_calloc(png_ptr, number*size) instead, and can call
+png_free() instead of png_zfree().
Support for dithering was disabled by default in libpng-1.4.0, because
-been well tested and doesn't actually "dither". The code was not
+it has not been well tested and doesn't actually "dither".
+The code was not
removed, however, and could be enabled by building libpng with
PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
was reenabled, but the function was renamed png_set_quantize() to
reflect more accurately what it actually does. At the same time,
the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
-PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS.
+PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED
+was renamed to PNG_READ_QUANTIZE_SUPPORTED.
We removed the trailing '.' from the warning and error messages.
-.SH X. Detecting libpng
+.SH XI. Changes to Libpng from version 1.4.x to 1.5.x
+
+From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
+function) incorrectly returned a value of type png_uint_32.
+
+Checking for invalid palette index on read or write was added at libpng
+1.5.10. When an invalid index is found, libpng issues a benign error.
+This is enabled by default because this condition is an error according
+to the PNG specification, Clause 11.3.2, but the error can be ignored in
+each png_ptr with
+
+ png_set_check_for_invalid_index(png_ptr, allowed);
+
+ allowed - one of
+ 0: disable benign error (accept the
+ invalid data without warning).
+ 1: enable benign error (treat the
+ invalid data as an error or a
+ warning).
+
+If the error is ignored, or if png_benign_error() treats it as a warning,
+any invalid pixels are decoded as opaque black by the decoder and written
+as-is by the encoder.
+
+Retrieving the maximum palette index found was added at libpng-1.5.15.
+This statement must appear after png_read_png() or png_read_image() while
+reading, and after png_write_png() or png_write_image() while writing.
+
+ int max_palette = png_get_palette_max(png_ptr, info_ptr);
+
+This will return the maximum palette index found in the image, or "-1" if
+the palette was not checked, or "0" if no palette was found. Note that this
+does not account for any palette index used by ancillary chunks such as the
+bKGD chunk; you must check those separately to determine the maximum
+palette index actually used.
+
+A. Changes that affect users of libpng
+
+There are no substantial API changes between the non-deprecated parts of
+the 1.4.5 API and the 1.5.0 API; however, the ability to directly access
+members of the main libpng control structures, png_struct and png_info,
+deprecated in earlier versions of libpng, has been completely removed from
+libpng 1.5.
+
+We no longer include zlib.h in png.h. The include statement has been moved
+to pngstruct.h, where it is not accessible by applications. Applications that
+need access to information in zlib.h will need to add the '#include "zlib.h"'
+directive. It does not matter whether this is placed prior to or after
+the '"#include png.h"' directive.
+
+The png_sprintf(), png_strcpy(), and png_strncpy() macros are no longer used
+and were removed.
+
+We moved the png_strlen(), png_memcpy(), png_memset(), and png_memcmp()
+macros into a private header file (pngpriv.h) that is not accessible to
+applications.
+
+In png_get_iCCP, the type of "profile" was changed from png_charpp
+to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
+
+There are changes of form in png.h, including new and changed macros to
+declare parts of the API. Some API functions with arguments that are
+pointers to data not modified within the function have been corrected to
+declare these arguments with PNG_CONST.
+
+Much of the internal use of C macros to control the library build has also
+changed and some of this is visible in the exported header files, in
+particular the use of macros to control data and API elements visible
+during application compilation may require significant revision to
+application code. (It is extremely rare for an application to do this.)
+
+Any program that compiled against libpng 1.4 and did not use deprecated
+features or access internal library structures should compile and work
+against libpng 1.5, except for the change in the prototype for
+png_get_iCCP() and png_set_iCCP() API functions mentioned above.
+
+libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of
+interlaced images. The macros return the number of rows and columns in
+each pass and information that can be used to de-interlace and (if
+absolutely necessary) interlace an image.
+
+libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls
+the application-provided png_longjmp_ptr on the internal, but application
+initialized, longjmp buffer. It is provided as a convenience to avoid
+the need to use the png_jmpbuf macro, which had the unnecessary side
+effect of resetting the internal png_longjmp_ptr value.
+
+libpng 1.5.0 includes a complete fixed point API. By default this is
+present along with the corresponding floating point API. In general the
+fixed point API is faster and smaller than the floating point one because
+the PNG file format used fixed point, not floating point. This applies
+even if the library uses floating point in internal calculations. A new
+macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library
+uses floating point arithmetic (the default) or fixed point arithmetic
+internally for performance critical calculations such as gamma correction.
+In some cases, the gamma calculations may produce slightly different
+results. This has changed the results in png_rgb_to_gray and in alpha
+composition (png_set_background for example). This applies even if the
+original image was already linear (gamma == 1.0) and, therefore, it is
+not necessary to linearize the image. This is because libpng has *not*
+been changed to optimize that case correctly, yet.
+
+Fixed point support for the sCAL chunk comes with an important caveat;
+the sCAL specification uses a decimal encoding of floating point values
+and the accuracy of PNG fixed point values is insufficient for
+representation of these values. Consequently a "string" API
+(png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading
+arbitrary sCAL chunks in the absence of either the floating point API or
+internal floating point calculations.
+
+Applications no longer need to include the optional distribution header
+file pngusr.h or define the corresponding macros during application
+build in order to see the correct variant of the libpng API. From 1.5.0
+application code can check for the corresponding _SUPPORTED macro:
+
+#ifdef PNG_INCH_CONVERSIONS_SUPPORTED
+ /* code that uses the inch conversion APIs. */
+#endif
+
+This macro will only be defined if the inch conversion functions have been
+compiled into libpng. The full set of macros, and whether or not support
+has been compiled in, are available in the header file pnglibconf.h.
+This header file is specific to the libpng build. Notice that prior to
+1.5.0 the _SUPPORTED macros would always have the default definition unless
+reset by pngusr.h or by explicit settings on the compiler command line.
+These settings may produce compiler warnings or errors in 1.5.0 because
+of macro redefinition.
+
+From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
+function) incorrectly returned a value of type png_uint_32. libpng 1.5.0
+is consistent with the implementation in 1.4.5 and 1.2.x (where the macro
+did not exist.)
+
+Applications can now choose whether to use these macros or to call the
+corresponding function by defining PNG_USE_READ_MACROS or
+PNG_NO_USE_READ_MACROS before including png.h. Notice that this is
+only supported from 1.5.0 -defining PNG_NO_USE_READ_MACROS prior to 1.5.0
+will lead to a link failure.
+
+Prior to libpng-1.5.4, the zlib compressor used the same set of parameters
+when compressing the IDAT data and textual data such as zTXt and iCCP.
+In libpng-1.5.4 we reinitialized the zlib stream for each type of data.
+We added five png_set_text_*() functions for setting the parameters to
+use with textual data.
+
+Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
+option was off by default, and slightly inaccurate scaling occurred.
+This option can no longer be turned off, and the choice of accurate
+or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8()
+API for accurate scaling or the old png_set_strip_16_to_8() API for simple
+chopping.
+
+Prior to libpng-1.5.4, the png_set_user_limits() function could only be
+used to reduce the width and height limits from the value of
+PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said
+that it could be used to override them. Now this function will reduce or
+increase the limits.
+
+Starting in libpng-1.5.10, the user limits can be set en masse with the
+configuration option PNG_SAFE_LIMITS_SUPPORTED. If this option is enabled,
+a set of "safe" limits is applied in pngpriv.h. These can be overridden by
+application calls to png_set_user_limits(), png_set_user_chunk_cache_max(),
+and/or png_set_user_malloc_max() that increase or decrease the limits. Also,
+in libpng-1.5.10 the default width and height limits were increased
+from 1,000,000 to 0x7ffffff (i.e., made unlimited). Therefore, the
+limits are now
+ default safe
+ png_user_width_max 0x7fffffff 1,000,000
+ png_user_height_max 0x7fffffff 1,000,000
+ png_user_chunk_cache_max 0 (unlimited) 128
+ png_user_chunk_malloc_max 0 (unlimited) 8,000,000
+
+B. Changes to the build and configuration of libpng
+
+Details of internal changes to the library code can be found in the CHANGES
+file and in the GIT repository logs. These will be of no concern to the vast
+majority of library users or builders; however, the few who configure libpng
+to a non-default feature set may need to change how this is done.
+
+There should be no need for library builders to alter build scripts if
+these use the distributed build support - configure or the makefiles -
+however, users of the makefiles may care to update their build scripts
+to build pnglibconf.h where the corresponding makefile does not do so.
+
+Building libpng with a non-default configuration has changed completely.
+The old method using pngusr.h should still work correctly even though the
+way pngusr.h is used in the build has been changed; however, library
+builders will probably want to examine the changes to take advantage of
+new capabilities and to simplify their build system.
+
+B.1 Specific changes to library configuration capabilities
+
+The library now supports a complete fixed point implementation and can
+thus be used on systems that have no floating point support or very
+limited or slow support. Previously gamma correction, an essential part
+of complete PNG support, required reasonably fast floating point.
+
+As part of this the choice of internal implementation has been made
+independent of the choice of fixed versus floating point APIs and all the
+missing fixed point APIs have been implemented.
+
+The exact mechanism used to control attributes of API functions has
+changed. A single set of operating system independent macro definitions
+is used and operating system specific directives are defined in
+pnglibconf.h
+
+As part of this the mechanism used to choose procedure call standards on
+those systems that allow a choice has been changed. At present this only
+affects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systems
+running on Intel processors. As before, PNGAPI is defined where required
+to control the exported API functions; however, two new macros, PNGCBAPI
+and PNGCAPI, are used instead for callback functions (PNGCBAPI) and
+(PNGCAPI) for functions that must match a C library prototype (currently
+only png_longjmp_ptr, which must match the C longjmp function.) The new
+approach is documented in pngconf.h
+
+Despite these changes, libpng 1.5.0 only supports the native C function
+calling standard on those platforms tested so far (__cdecl on Microsoft
+Windows). This is because the support requirements for alternative
+calling conventions seem to no longer exist. Developers who find it
+necessary to set PNG_API_RULE to 1 should advise the mailing list
+(png-mng-implement) of this and library builders who use Openwatcom and
+therefore set PNG_API_RULE to 2 should also contact the mailing list.
+
+A new test program, pngvalid, is provided in addition to pngtest.
+pngvalid validates the arithmetic accuracy of the gamma correction
+calculations and includes a number of validations of the file format.
+A subset of the full range of tests is run when "make check" is done
+(in the 'configure' build.) pngvalid also allows total allocated memory
+usage to be evaluated and performs additional memory overwrite validation.
+
+Many changes to individual feature macros have been made. The following
+are the changes most likely to be noticed by library builders who
+configure libpng:
+
+1) All feature macros now have consistent naming:
+
+#define PNG_NO_feature turns the feature off
+#define PNG_feature_SUPPORTED turns the feature on
+
+pnglibconf.h contains one line for each feature macro which is either:
+
+#define PNG_feature_SUPPORTED
+
+if the feature is supported or:
+
+/*#undef PNG_feature_SUPPORTED*/
+
+if it is not. Library code consistently checks for the 'SUPPORTED' macro.
+It does not, and libpng applications should not, check for the 'NO' macro
+which will not normally be defined even if the feature is not supported.
+The 'NO' macros are only used internally for setting or not setting the
+corresponding 'SUPPORTED' macros.
+
+Compatibility with the old names is provided as follows:
+
+PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
+
+And the following definitions disable the corresponding feature:
+
+PNG_SETJMP_NOT_SUPPORTED disables SETJMP
+PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS
+PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV
+PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS
+PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS
+PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
+
+Library builders should remove use of the above, inconsistent, names.
+
+2) Warning and error message formatting was previously conditional on
+the STDIO feature. The library has been changed to use the
+CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled
+the library no longer uses the printf(3) functions, even though the
+default read/write implementations use (FILE) style stdio.h functions.
+
+3) Three feature macros now control the fixed/floating point decisions:
+
+PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
+
+PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in
+practice these are normally required internally anyway (because the PNG
+file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT
+merely stops the function from being exported.
+
+PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating
+point implementation or the fixed point one. Typically the fixed point
+implementation is larger and slower than the floating point implementation
+on a system that supports floating point; however, it may be faster on a
+system which lacks floating point hardware and therefore uses a software
+emulation.
+
+4) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the
+functions to read and write ints to be disabled independently of
+PNG_USE_READ_MACROS, which allows libpng to be built with the functions
+even though the default is to use the macros - this allows applications
+to choose at app buildtime whether or not to use macros (previously
+impossible because the functions weren't in the default build.)
+
+B.2 Changes to the configuration mechanism
+
+Prior to libpng-1.5.0 library builders who needed to configure libpng
+had either to modify the exported pngconf.h header file to add system
+specific configuration or had to write feature selection macros into
+pngusr.h and cause this to be included into pngconf.h by defining
+PNG_USER_CONFIG. The latter mechanism had the disadvantage that an
+application built without PNG_USER_CONFIG defined would see the
+unmodified, default, libpng API and thus would probably fail to link.
+
+These mechanisms still work in the configure build and in any makefile
+build that builds pnglibconf.h, although the feature selection macros
+have changed somewhat as described above. In 1.5.0, however, pngusr.h is
+processed only once, when the exported header file pnglibconf.h is built.
+pngconf.h no longer includes pngusr.h, therefore pngusr.h is ignored after the
+build of pnglibconf.h and it is never included in an application build.
+
+The rarely used alternative of adding a list of feature macros to the
+CFLAGS setting in the build also still works; however, the macros will be
+copied to pnglibconf.h and this may produce macro redefinition warnings
+when the individual C files are compiled.
+
+All configuration now only works if pnglibconf.h is built from
+scripts/pnglibconf.dfa. This requires the program awk. Brian Kernighan
+(the original author of awk) maintains C source code of that awk and this
+and all known later implementations (often called by subtly different
+names - nawk and gawk for example) are adequate to build pnglibconf.h.
+The Sun Microsystems (now Oracle) program 'awk' is an earlier version
+and does not work; this may also apply to other systems that have a
+functioning awk called 'nawk'.
+
+Configuration options are now documented in scripts/pnglibconf.dfa. This
+file also includes dependency information that ensures a configuration is
+consistent; that is, if a feature is switched off dependent features are
+also removed. As a recommended alternative to using feature macros in
+pngusr.h a system builder may also define equivalent options in pngusr.dfa
+(or, indeed, any file) and add that to the configuration by setting
+DFA_XTRA to the file name. The makefiles in contrib/pngminim illustrate
+how to do this, and a case where pngusr.h is still required.
+
+.SH XII. Changes to Libpng from version 1.5.x to 1.6.x
+
+A "simplified API" has been added (see documentation in png.h and a simple
+example in contrib/examples/pngtopng.c). The new publicly visible API
+includes the following:
+
+ macros:
+ PNG_FORMAT_*
+ PNG_IMAGE_*
+ structures:
+ png_control
+ png_image
+ read functions
+ png_image_begin_read_from_file()
+ png_image_begin_read_from_stdio()
+ png_image_begin_read_from_memory()
+ png_image_finish_read()
+ png_image_free()
+ write functions
+ png_image_write_to_file()
+ png_image_write_to_stdio()
+
+Starting with libpng-1.6.0, you can configure libpng to prefix all exported
+symbols, using the PNG_PREFIX macro.
+
+We no longer include string.h in png.h. The include statement has been moved
+to pngpriv.h, where it is not accessible by applications. Applications that
+need access to information in string.h must add an '#include "string.h"'
+directive. It does not matter whether this is placed prior to or after
+the '"#include png.h"' directive.
+
+The following API are now DEPRECATED:
+ png_info_init_3()
+ png_convert_to_rfc1123() which has been replaced
+ with png_convert_to_rfc1123_buffer()
+ png_data_freer()
+ png_malloc_default()
+ png_free_default()
+ png_reset_zstream()
+
+The following have been removed:
+ png_get_io_chunk_name(), which has been replaced
+ with png_get_io_chunk_type(). The new
+ function returns a 32-bit integer instead of
+ a string.
+ The png_sizeof(), png_strlen(), png_memcpy(), png_memcmp(), and
+ png_memset() macros are no longer used in the libpng sources and
+ have been removed. These had already been made invisible to applications
+ (i.e., defined in the private pngpriv.h header file) since libpng-1.5.0.
+
+The signatures of many exported functions were changed, such that
+ png_structp became png_structrp or png_const_structrp
+ png_infop became png_inforp or png_const_inforp
+where "rp" indicates a "restricted pointer".
+
+Error detection in some chunks has improved; in particular the iCCP chunk
+reader now does pretty complete validation of the basic format. Some bad
+profiles that were previously accepted are now rejected, in particular the
+very old broken Microsoft/HP sRGB profile. The PNG spec requirement that
+only grayscale profiles may appear in images with color type 0 or 4 and that
+even if the image only contains gray pixels, only RGB profiles may appear
+in images with color type 2, 3, or 6, is now enforced. The sRGB chunk
+is allowed to appear in images with any color type.
+
+The library now issues an error if the application attempts to set a
+transform after it calls png_read_update_info().
+
+The library now issues a warning if both background processing and RGB to
+gray are used when gamma correction happens. As with previous versions of
+the library the results are numerically very incorrect in this case.
+
+There are some minor arithmetic changes in some transforms such as
+png_set_background(), that might be detected by certain regression tests.
+
+Unknown chunk handling has been improved internally, without any API change.
+This adds more correct option control of the unknown handling, corrects
+a pre-existing bug where the per-chunk 'keep' setting is ignored, and makes
+it possible to skip IDAT chunks in the sequential reader.
+
+The machine-generated configure files are no longer included in branches
+libpng16 and later of the GIT repository. They continue to be included
+in the tarball releases, however.
+
+.SH XIII. Detecting libpng
The png_get_io_ptr() function has been present since libpng-0.88, has never
changed, and is unaffected by conditional compilation macros. It is the
AC_CHECK_LIB(png, png_get_io_ptr, ...
-.SH XI. Source code repository
+.SH XV. Source code repository
Since about February 2009, version 1.2.34, libpng has been under "git" source
control. The git repository was built from old libpng-x.y.z.tar.gz files
going back to version 0.70. You can access the git repository (read only)
at
- git://libpng.git.sourceforge.net/gitroot/libpng
+ git://git.code.sf.net/p/libpng/code
-or you can browse it via "gitweb" at
+or you can browse it with a web browser by selecting the "code" button at
- http://libpng.git.sourceforge.net/git/gitweb.cgi?p=libpng
+ https://sourceforge.net/projects/libpng
Patches can be sent to glennrp at users.sourceforge.net or to
png-mng-implement at lists.sourceforge.net or you can upload them to
http://libpng.sourceforge.net
-.SH XII. Coding style
+We also accept patches built from the tar or zip distributions, and
+simple verbal discriptions of bug fixes, reported either to the
+SourceForge bug tracker, to the png-mng-implement at lists.sf.net
+mailing list, or directly to glennrp.
+
+.SH XV. Coding style
Our coding style is similar to the "Allman" style, with curly
braces on separate lines:
exported functions are marked with PNGAPI:
/* This is a public function that is visible to
- * application programers. It does thus-and-so.
+ * application programmers. It does thus-and-so.
*/
void PNGAPI
png_exported_function(png_ptr, png_info, foo)
pngpriv.h
above the comment that says
- /* Maintainer: Put new private prototypes here ^ and in libpngpf.3 */
+ /* Maintainer: Put new private prototypes here ^ */
+
+We put a space after the "sizeof" operator and we omit the
+optional parentheses around its argument when the argument
+is an expression, not a type name, and we always enclose the
+sizeof operator, with its argument, in parentheses:
+
+ (sizeof (png_uint_32))
+ (sizeof array)
-The names of all exported functions and variables begin
-with "png_", and all publicly visible C preprocessor
-macros begin with "PNG_".
+Prior to libpng-1.6.0 we used a "png_sizeof()" macro, formatted as
+though it were a function.
+
+To avoid polluting the global namespace, the names of all exported
+functions and variables begin with "png_", and all publicly visible C
+preprocessor macros begin with "PNG". We request that applications that
+use libpng *not* begin any of their own symbols with either of these strings.
We put a space after each comma and after each semicolon
-in "for" statments, and we put spaces before and after each
+in "for" statements, and we put spaces before and after each
C binary operator and after "for" or "while", and before
"?". We don't put a space between a typecast and the expression
being cast, nor do we put one between a function name and the
for (i = 2; i > 0; --i)
y[i] = a(x) + (int)b;
-We prefer #ifdef and #ifndef to #if defined() and if !defined()
-when there is only one macro being tested.
+We prefer #ifdef and #ifndef to #if defined() and #if !defined()
+when there is only one macro being tested. We always use parentheses
+with "defined".
+
+We prefer to express integers that are used as bit masks in hex format,
+with an even number of lower-case hex digits (e.g., 0x00, 0xff, 0x0100).
+
+We prefer to use underscores in variable names rather than camelCase, except
+for a few type names that we inherit from zlib.h.
We do not use the TAB character for indentation in the C sources.
Other rules can be inferred by inspecting the libpng source.
-.SH XIII. Y2K Compliance in libpng
+.SH XVI. Y2K Compliance in libpng
-September 23, 2010
+April 25, 2013
Since the PNG Development group is an ad-hoc body, we can't make
an official declaration.
This is your unofficial assurance that libpng from version 0.71 and
-upward through 1.4.4 are Y2K compliant. It is my belief that earlier
+upward through 1.6.2 are Y2K compliant. It is my belief that earlier
versions were also Y2K compliant.
-Libpng only has three year fields. One is a 2-byte unsigned integer that
-will hold years up to 65535. The other two hold the date in text
-format, and will hold years up to 9999.
+Libpng only has two year fields. One is a 2-byte unsigned integer
+that will hold years up to 65535. The other, which is deprecated,
+holds the date in text format, and will hold years up to 9999.
The integer is
"png_uint_16 year" in png_time_struct.
-The strings are
- "png_charp time_buffer" in png_struct and
- "near_time_buffer", which is a local character string in png.c.
+The string is
+ "char time_buffer[29]" in png_struct. This is no longer used
+in libpng-1.6.x and will be removed from libpng-1.7.0.
There are seven time-related functions:
1.4.1beta01-03 14 10401 14.so.14.1[.0]
1.4.1rc01 14 10401 14.so.14.1[.0]
1.4.1beta04-12 14 10401 14.so.14.1[.0]
- 1.4.1rc02-04 14 10401 14.so.14.1[.0]
1.4.1 14 10401 14.so.14.1[.0]
- 1.4.2beta01 14 10402 14.so.14.2[.0]
- 1.4.2rc02-06 14 10402 14.so.14.2[.0]
1.4.2 14 10402 14.so.14.2[.0]
- 1.4.3beta01-05 14 10403 14.so.14.3[.0]
- 1.4.3rc01-03 14 10403 14.so.14.3[.0]
1.4.3 14 10403 14.so.14.3[.0]
- 1.4.4beta01-08 14 10404 14.so.14.4[.0]
- 1.4.4rc01-06 14 10404 14.so.14.4[.0]
+ 1.4.4 14 10404 14.so.14.4[.0]
+ 1.5.0beta01-58 15 10500 15.so.15.0[.0]
+ 1.5.0rc01-07 15 10500 15.so.15.0[.0]
+ 1.5.0 15 10500 15.so.15.0[.0]
+ 1.5.1beta01-11 15 10501 15.so.15.1[.0]
+ 1.5.1rc01-02 15 10501 15.so.15.1[.0]
+ 1.5.1 15 10501 15.so.15.1[.0]
+ 1.5.2beta01-03 15 10502 15.so.15.2[.0]
+ 1.5.2rc01-03 15 10502 15.so.15.2[.0]
+ 1.5.2 15 10502 15.so.15.2[.0]
+ 1.5.3beta01-10 15 10503 15.so.15.3[.0]
+ 1.5.3rc01-02 15 10503 15.so.15.3[.0]
+ 1.5.3beta11 15 10503 15.so.15.3[.0]
+ 1.5.3 [omitted]
+ 1.5.4beta01-08 15 10504 15.so.15.4[.0]
+ 1.5.4rc01 15 10504 15.so.15.4[.0]
+ 1.5.4 15 10504 15.so.15.4[.0]
+ 1.5.5beta01-08 15 10505 15.so.15.5[.0]
+ 1.5.5rc01 15 10505 15.so.15.5[.0]
+ 1.5.5 15 10505 15.so.15.5[.0]
+ 1.5.6beta01-07 15 10506 15.so.15.6[.0]
+ 1.5.6rc01-03 15 10506 15.so.15.6[.0]
+ 1.5.6 15 10506 15.so.15.6[.0]
+ 1.5.7beta01-05 15 10507 15.so.15.7[.0]
+ 1.5.7rc01-03 15 10507 15.so.15.7[.0]
+ 1.5.7 15 10507 15.so.15.7[.0]
+ 1.6.0beta01-40 16 10600 16.so.16.0[.0]
+ 1.6.0rc01-08 16 10600 16.so.16.0[.0]
+ 1.6.0 16 10600 16.so.16.0[.0]
+ 1.6.1beta01-09 16 10601 16.so.16.1[.0]
+ 1.6.1rc01 16 10601 16.so.16.1[.0]
+ 1.6.1 16 10601 16.so.16.1[.0]
+ 1.6.2beta01 16 10602 16.so.16.2[.0]
+ 1.6.2rc01-06 16 10602 16.so.16.2[.0]
+ 1.6.2 16 10602 16.so.16.2[.0]
Henceforth the source version will match the shared-library minor
and patch numbers; the shared-library major version number will be
.SH "SEE ALSO"
.BR "png"(5), " libpngpf"(3), " zlib"(3), " deflate"(5), " " and " zlib"(5)
+
.LP
.IR libpng :
.IP
Thanks to Frank J. T. Wojcik for helping with the documentation.
-Libpng version 1.4.4 - September 23, 2010:
+Libpng version 1.6.2 - April 25, 2013:
Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
This code is released under the libpng license.
-libpng versions 1.2.6, August 15, 2004, through 1.4.4, September 23, 2010, are
+libpng versions 1.2.6, August 15, 2004, through 1.6.2, April 25, 2013, are
Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are
distributed according to the same disclaimer and license as libpng-1.2.5
with the following individual added to the list of Contributing Authors
Glenn Randers-Pehrson
glennrp at users.sourceforge.net
-September 23, 2010
+April 25, 2013
.\" end of man page
projects / wxWidgets.git / blobdiff