1 .TH LIBPNG 3 "November 3, 2011"
3 libpng \- Portable Network Graphics (PNG) Reference Library 1.5.6
11 \fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
15 \fBvoid png_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
19 \fBvoid png_build_grayscale_palette (int \fP\fIbit_depth\fP\fB, png_colorp \fIpalette\fP\fB);\fP
23 \fBpng_voidp png_calloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
27 \fBvoid png_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
31 \fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
35 \fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
39 \fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
43 \fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
47 \fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
51 \fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
55 \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
59 \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
63 \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
67 \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
71 \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
75 \fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
79 \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
83 \fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
87 \fBvoid png_err (png_structp \fIpng_ptr\fP\fB);\fP
91 \fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
95 \fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
99 \fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
103 \fBvoid png_free_default (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
107 \fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
111 \fBpng_byte png_get_bit_depth (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
115 \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
119 \fBpng_byte png_get_channels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
123 \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
127 \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
131 \fBpng_uint_32 png_get_cHRM_XYZ (png_structp \fIpng_ptr,
133 \fBpng_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*red_X\fP\fB, double \fP\fI*red_Y\fP\fB, double \fI*red_Z,
135 \fBdouble \fP\fI*green_X\fP\fB, double \fP\fI*green_Y\fP\fB, double \fP\fI*green_Z\fP\fB, double \fI*blue_X,
137 \fBdouble \fP\fI*blue_Y\fP\fB, double \fI*blue_Z\fP\fB);\fP
141 \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
145 \fBpng_uint_32 png_get_chunk_cache_max (png_const_structp \fIpng_ptr\fP\fB);\fP
149 \fBpng_alloc_size_t png_get_chunk_malloc_max (png_const_structp \fIpng_ptr\fP\fB);\fP
153 \fBpng_byte png_get_color_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
157 \fBpng_uint_32 png_get_compression_buffer_size (png_const_structp \fIpng_ptr\fP\fB);\fP
161 \fBpng_byte png_get_compression_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
165 \fBpng_byte png_get_copyright (png_const_structp \fIpng_ptr\fP\fB);\fP
169 \fBpng_uint_32 png_get_current_row_number \fI(png_const_structp\fP\fB);\fP
173 \fBpng_byte png_get_current_pass_number \fI(png_const_structp\fP\fB);\fP
177 \fBpng_voidp png_get_error_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
181 \fBpng_byte png_get_filter_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
185 \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
189 \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
193 \fBpng_byte png_get_header_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
197 \fBpng_byte png_get_header_version (png_const_structp \fIpng_ptr\fP\fB);\fP
201 \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
205 \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
209 \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
213 \fBpng_uint_32 png_get_image_height (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
217 \fBpng_uint_32 png_get_image_width (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
221 \fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
225 \fBpng_byte png_get_interlace_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
229 \fBpng_const_bytep png_get_io_chunk_name (png_structp \fIpng_ptr\fP\fB);\fP
233 \fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP
237 \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
241 \fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP
245 \fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
249 \fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
253 \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
257 \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
261 \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
265 \fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
269 \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
273 \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
277 \fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
281 \fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
285 \fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
289 \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
293 \fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr)
295 \fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
299 \fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
303 \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
307 \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
311 \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
315 \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
319 \fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
323 \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
327 \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
331 \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
335 \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
339 \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
343 \fB/* This function is really an inline macro. \fI*/
345 \fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
349 \fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP
353 \fB/* This function is really an inline macro. \fI*/
355 \fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
359 \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
363 \fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
367 \fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP
371 \fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
375 \fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP
379 \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
383 \fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
387 \fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
391 \fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
395 \fBpng_int_32 png_get_x_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
399 \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
403 \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
407 \fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
411 \fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
415 \fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
419 \fBpng_int_32 png_get_y_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
423 \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
427 \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
431 \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
435 \fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
439 \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
443 \fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP
447 \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
451 \fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
455 \fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
459 \fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP
463 \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
467 \fBpng_size_t png_process_data_pause \fP\fI(png_structp\fP\fB, int \fIsave\fP\fB);\fP
471 \fBpng_uint_32 png_process_data_skip \fI(png_structp\fP\fB);\fP
475 \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
479 \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
483 \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
487 \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
491 \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
495 \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
499 \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
503 \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
507 \fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP
511 \fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
515 \fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
519 \fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
523 \fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
527 \fBvoid png_set_alpha_mode (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, double \fIoutput_gamma\fP\fB);\fP
531 \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
535 \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
539 \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
543 \fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
547 \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
551 \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
555 \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
559 \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
563 \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 \fIgreen_Y,
565 \fBdouble \fP\fIgreen_Z\fP\fB, double \fP\fIblue_X\fP\fB, double \fP\fIblue_Y\fP\fB, double \fIblue_Z\fP\fB);\fP
569 \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
573 \fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
577 \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
581 \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
585 \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
589 \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
593 \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
597 \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
601 \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
605 \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
609 \fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP
613 \fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
617 \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
621 \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
625 \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
629 \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
633 \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
637 \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
641 \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
645 \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
649 \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
653 \fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
657 \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
661 \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
665 \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
669 \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
673 \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
677 \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
681 \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
685 \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
689 \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
693 \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
697 \fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
701 \fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
705 \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
709 \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
713 \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
717 \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
721 \fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
725 \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
729 \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
733 \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
737 \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
741 \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
745 \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
749 \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
753 \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
757 \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
761 \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
765 \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
769 \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
773 \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
777 \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
781 \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
785 \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
789 \fBvoid png_set_scale_16 (png_structp \fIpng_ptr\fP\fB);\fP
793 \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
797 \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
801 \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
805 \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
809 \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
813 \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
817 \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
821 \fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP
825 \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
829 \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
833 \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
837 \fBvoid png_set_text_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
841 \fBvoid png_set_text_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
845 \fBvoid png_set_text_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
849 \fBvoid png_set_text_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
853 \fBvoid \fP\fIpng_set_text_compression_method\fP\fB, (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod)\fP\fB);\fP
857 \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
861 \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
865 \fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP
869 \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
873 \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
877 \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
881 \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
885 \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
889 \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
893 \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
897 \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
901 \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
905 \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
909 \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
913 \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
917 \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
921 \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
925 \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
929 \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
933 \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
937 \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
941 \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
945 \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
949 \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
953 \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
957 \fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
961 \fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
965 \fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
972 library supports encoding, decoding, and various manipulations of
973 the Portable Network Graphics (PNG) format image files. It uses the
976 Following is a copy of the libpng-manual.txt file that accompanies libpng.
978 libpng-manual.txt - A description on how to use and modify libpng
980 libpng version 1.5.6 - November 3, 2011
981 Updated and distributed by Glenn Randers-Pehrson
982 <glennrp at users.sourceforge.net>
983 Copyright (c) 1998-2011 Glenn Randers-Pehrson
985 This document is released under the libpng license.
986 For conditions of distribution and use, see the disclaimer
991 libpng versions 0.97, January 1998, through 1.5.6 - November 3, 2011
992 Updated and distributed by Glenn Randers-Pehrson
993 Copyright (c) 1998-2011 Glenn Randers-Pehrson
995 libpng 1.0 beta 6 version 0.96 May 28, 1997
996 Updated and distributed by Andreas Dilger
997 Copyright (c) 1996, 1997 Andreas Dilger
999 libpng 1.0 beta 2 - version 0.88 January 26, 1996
1000 For conditions of distribution and use, see copyright
1001 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
1002 Schalnat, Group 42, Inc.
1004 Updated/rewritten per request in the libpng FAQ
1005 Copyright (c) 1995, 1996 Frank J. T. Wojcik
1006 December 18, 1995 & January 20, 1996
1010 This file describes how to use and modify the PNG reference library
1011 (known as libpng) for your own use. There are five sections to this
1012 file: introduction, structures, reading, writing, and modification and
1013 configuration notes for various special platforms. In addition to this
1014 file, example.c is a good starting point for using the library, as
1015 it is heavily commented and should include everything most people
1016 will need. We assume that libpng is already installed; see the
1017 INSTALL file for instructions on how to install libpng.
1019 For examples of libpng usage, see the files "example.c", "pngtest.c",
1020 and the files in the "contrib" directory, all of which are included in
1021 the libpng distribution.
1023 Libpng was written as a companion to the PNG specification, as a way
1024 of reducing the amount of time and effort it takes to support the PNG
1025 file format in application programs.
1027 The PNG specification (second edition), November 2003, is available as
1028 a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
1029 <http://www.w3.org/TR/2003/REC-PNG-20031110/
1030 The W3C and ISO documents have identical technical content.
1032 The PNG-1.2 specification is available at
1033 <http://www.libpng.org/pub/png/documents/>. It is technically equivalent
1034 to the PNG specification (second edition) but has some additional material.
1036 The PNG-1.0 specification is available
1037 as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
1038 W3C Recommendation <http://www.w3.org/TR/REC.png.html>.
1040 Some additional chunks are described in the special-purpose public chunks
1041 documents at <http://www.libpng.org/pub/png/documents/>.
1044 about PNG, and the latest version of libpng, can be found at the PNG home
1045 page, <http://www.libpng.org/pub/png/>.
1047 Most users will not have to modify the library significantly; advanced
1048 users may want to modify it more. All attempts were made to make it as
1049 complete as possible, while keeping the code easy to understand.
1050 Currently, this library only supports C. Support for other languages
1051 is being considered.
1053 Libpng has been designed to handle multiple sessions at one time,
1054 to be easily modifiable, to be portable to the vast majority of
1055 machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
1056 to use. The ultimate goal of libpng is to promote the acceptance of
1057 the PNG file format in whatever way possible. While there is still
1058 work to be done (see the TODO file), libpng should cover the
1059 majority of the needs of its users.
1061 Libpng uses zlib for its compression and decompression of PNG files.
1062 Further information about zlib, and the latest version of zlib, can
1063 be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
1064 The zlib compression utility is a general purpose utility that is
1065 useful for more than PNG files, and can be used without libpng.
1066 See the documentation delivered with zlib for more details.
1067 You can usually find the source files for the zlib utility wherever you
1068 find the libpng source files.
1070 Libpng is thread safe, provided the threads are using different
1071 instances of the structures. Each thread should have its own
1072 png_struct and png_info instances, and thus its own image.
1073 Libpng does not protect itself against two threads using the
1074 same instance of a structure.
1078 There are two main structures that are important to libpng, png_struct
1079 and png_info. Both are internal structures that are no longer exposed
1080 in the libpng interface (as of libpng 1.5.0).
1082 The png_info structure is designed to provide information about the
1083 PNG file. At one time, the fields of png_info were intended to be
1084 directly accessible to the user. However, this tended to cause problems
1085 with applications using dynamically loaded libraries, and as a result
1086 a set of interface functions for png_info (the png_get_*() and png_set_*()
1087 functions) was developed, and direct access to the png_info fields was
1090 The png_struct structure is the object used by the library to decode a
1091 single image. As of 1.5.0 this structure is also not exposed.
1093 Almost all libpng APIs require a pointer to a png_struct as the first argument.
1094 Many (in particular the png_set and png_get APIs) also require a pointer
1095 to png_info as the second argument. Some application visible macros
1096 defined in png.h designed for basic data access (reading and writing
1097 integers in the PNG format) don't take a png_info pointer, but it's almost
1098 always safe to assume that a (png_struct*) has to be passed to call an API
1101 You can have more than one png_info structure associated with an image,
1102 as illustrated in pngtest.c, one for information valid prior to the
1103 IDAT chunks and another (called "end_info" below) for things after them.
1105 The png.h header file is an invaluable reference for programming with libpng.
1106 And while I'm on the topic, make sure you include the libpng header file:
1110 and also (as of libpng-1.5.0) the zlib header file, if you need it:
1116 The png.h header file defines a number of integral types used by the
1117 APIs. Most of these are fairly obvious; for example types corresponding
1118 to integers of particular sizes and types for passing color values.
1120 One exception is how non-integral numbers are handled. For application
1121 convenience most APIs that take such numbers have C (double) arguments,
1122 however internally PNG, and libpng, use 32 bit signed integers and encode
1123 the value by multiplying by 100,000. As of libpng 1.5.0 a convenience
1124 macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point)
1125 which is simply (png_int_32).
1127 All APIs that take (double) arguments also have a matching API that
1128 takes the corresponding fixed point integer arguments. The fixed point
1129 API has the same name as the floating point one with "_fixed" appended.
1130 The actual range of values permitted in the APIs is frequently less than
1131 the full range of (png_fixed_point) (-21474 to +21474). When APIs require
1132 a non-negative argument the type is recorded as png_uint_32 above. Consult
1133 the header file and the text below for more information.
1135 Special care must be take with sCAL chunk handling because the chunk itself
1136 uses non-integral values encoded as strings containing decimal floating point
1137 numbers. See the comments in the header file.
1141 The main header file function declarations are frequently protected by C
1142 preprocessing directives of the form:
1144 #ifdef PNG_feature_SUPPORTED
1148 #ifdef PNG_feature_SUPPORTED
1152 The library can be built without support for these APIs, although a
1153 standard build will have all implemented APIs. Application programs
1154 should check the feature macros before using an API for maximum
1155 portability. From libpng 1.5.0 the feature macros set during the build
1156 of libpng are recorded in the header file "pnglibconf.h" and this file
1157 is always included by png.h.
1159 If you don't need to change the library configuration from the default, skip to
1160 the next section ("Reading").
1162 Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all
1163 of the build project files in the 'projects' directory simply copy
1164 scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build
1165 systems do not permit easy auto-configuration of the library - they only
1166 support the default configuration.
1168 The easiest way to make minor changes to the libpng configuration when
1169 auto-configuration is supported is to add definitions to the command line
1170 using (typically) CPPFLAGS. For example:
1172 CPPFLAGS=-DPNG_NO_FLOATING_ARITHMETIC
1174 will change the internal libpng math implementation for gamma correction and
1175 other arithmetic calculations to fixed point, avoiding the need for fast
1176 floating point support. The result can be seen in the generated pnglibconf.h -
1177 make sure it contains the changed feature macro setting.
1179 If you need to make more extensive configuration changes - more than one or two
1180 feature macro settings - you can either add -DPNG_USER_CONFIG to the build
1181 command line and put a list of feature macro settings in pngusr.h or you can set
1182 DFA_XTRA (a makefile variable) to a file containing the same information in the
1183 form of 'option' settings.
1185 A. Changing pnglibconf.h
1187 A variety of methods exist to build libpng. Not all of these support
1188 reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be
1189 rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand.
1191 Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to
1192 pnglibconf.h and changing the lines defining the supported features, paying
1193 very close attention to the 'option' information in scripts/pnglibconf.dfa
1194 that describes those features and their requirements. This is easy to get
1197 B. Configuration using DFA_XTRA
1199 Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later
1200 variant such as 'nawk' or 'gawk', is available. The configure build will
1201 automatically find an appropriate awk and build pnglibconf.h.
1202 The scripts/pnglibconf.mak file contains a set of make rules for doing the
1203 same thing if configure is not used, and many of the makefiles in the scripts
1204 directory use this approach.
1206 When rebuilding simply write a new file containing changed options and set
1207 DFA_XTRA to the name of this file. This causes the build to append the new file
1208 to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines
1209 of the following forms:
1213 This turns all optional features off. Include it at the start of pngusr.dfa to
1214 make it easier to build a minimal configuration. You will need to turn at least
1215 some features on afterward to enable either reading or writing code, or both.
1220 Enable or disable a single feature. This will automatically enable other
1221 features required by a feature that is turned on or disable other features that
1222 require a feature which is turned off. Conflicting settings will cause an error
1223 message to be emitted by awk.
1225 setting feature default value
1227 Changes the default value of setting 'feature' to 'value'. There are a small
1228 number of settings listed at the top of pnglibconf.h, they are documented in the
1229 source code. Most of these values have performance implications for the library
1230 but most of them have no visible effect on the API. Some can also be overridden
1233 This method of building a customized pnglibconf.h is illustrated in
1234 contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and
1235 pngusr.dfa in these directories.
1237 C. Configuration using PNG_USR_CONFIG
1239 If -DPNG_USR_CONFIG is added to the CFLAGS when pnglibconf.h is built the file
1240 pngusr.h will automatically be included before the options in
1241 scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only
1242 macro definitions turning features on or off or setting settings.
1244 Apart from the global setting "everything = off" all the options listed above
1245 can be set using macros in pngusr.h:
1247 #define PNG_feature_SUPPORTED
1253 #define PNG_NO_feature
1259 #define PNG_feature value
1263 setting feature default value
1265 Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the
1266 pngusr file you supply override the contents of scripts/pnglibconf.dfa
1268 If confusing or incomprehensible behavior results it is possible to
1269 examine the intermediate file pnglibconf.dfn to find the full set of
1270 dependency information for each setting and option. Simply locate the
1271 feature in the file and read the C comments that precede it.
1273 This method is also illustrated in the contrib/pngminim/* makefiles and
1278 We'll now walk you through the possible functions to call when reading
1279 in a PNG file sequentially, briefly explaining the syntax and purpose
1280 of each one. See example.c and png.h for more detail. While
1281 progressive reading is covered in the next section, you will still
1282 need some of the functions discussed in this section to read a PNG
1287 You will want to do the I/O initialization(*) before you get into libpng,
1288 so if it doesn't work, you don't have much to undo. Of course, you
1289 will also want to insure that you are, in fact, dealing with a PNG
1290 file. Libpng provides a simple check to see if a file is a PNG file.
1291 To use it, pass in the first 1 to 8 bytes of the file to the function
1292 png_sig_cmp(), and it will return 0 (false) if the bytes match the
1293 corresponding bytes of the PNG signature, or nonzero (true) otherwise.
1294 Of course, the more bytes you pass in, the greater the accuracy of the
1297 If you are intending to keep the file pointer open for use in libpng,
1298 you must ensure you don't read more than 8 bytes from the beginning
1299 of the file, and you also have to make a call to png_set_sig_bytes_read()
1300 with the number of bytes you read from the beginning. Libpng will
1301 then only check the bytes (if any) that your program didn't read.
1303 (*): If you are not using the standard I/O functions, you will need
1304 to replace them with custom functions. See the discussion under
1308 FILE *fp = fopen(file_name, "rb");
1314 fread(header, 1, number, fp);
1315 is_png = !png_sig_cmp(header, 0, number);
1323 Next, png_struct and png_info need to be allocated and initialized. In
1324 order to ensure that the size of these structures is correct even with a
1325 dynamically linked libpng, there are functions to initialize and
1326 allocate the structures. We also pass the library version, optional
1327 pointers to error handling functions, and a pointer to a data struct for
1328 use by the error functions, if necessary (the pointer and functions can
1329 be NULL if the default error handlers are to be used). See the section
1330 on Changes to Libpng below regarding the old initialization functions.
1331 The structure allocation functions quietly return NULL if they fail to
1332 create the structure, so your application should check for that.
1334 png_structp png_ptr = png_create_read_struct
1335 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1336 user_error_fn, user_warning_fn);
1341 png_infop info_ptr = png_create_info_struct(png_ptr);
1345 png_destroy_read_struct(&png_ptr,
1346 (png_infopp)NULL, (png_infopp)NULL);
1350 If you want to use your own memory allocation routines,
1351 use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use
1352 png_create_read_struct_2() instead of png_create_read_struct():
1354 png_structp png_ptr = png_create_read_struct_2
1355 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1356 user_error_fn, user_warning_fn, (png_voidp)
1357 user_mem_ptr, user_malloc_fn, user_free_fn);
1359 The error handling routines passed to png_create_read_struct()
1360 and the memory alloc/free routines passed to png_create_struct_2()
1361 are only necessary if you are not using the libpng supplied error
1362 handling and memory alloc/free functions.
1364 When libpng encounters an error, it expects to longjmp back
1365 to your routine. Therefore, you will need to call setjmp and pass
1366 your png_jmpbuf(png_ptr). If you read the file from different
1367 routines, you will need to update the longjmp buffer every time you enter
1368 a new routine that will call a png_*() function.
1370 See your documentation of setjmp/longjmp for your compiler for more
1371 information on setjmp/longjmp. See the discussion on libpng error
1372 handling in the Customizing Libpng section below for more information
1373 on the libpng error handling. If an error occurs, and libpng longjmp's
1374 back to your setjmp, you will want to call png_destroy_read_struct() to
1377 if (setjmp(png_jmpbuf(png_ptr)))
1379 png_destroy_read_struct(&png_ptr, &info_ptr,
1385 Pass (png_infopp)NULL instead of &end_info if you didn't create
1386 an end_info structure.
1388 If you would rather avoid the complexity of setjmp/longjmp issues,
1389 you can compile libpng with PNG_NO_SETJMP, in which case
1390 errors will result in a call to PNG_ABORT() which defaults to abort().
1392 You can #define PNG_ABORT() to a function that does something
1393 more useful than abort(), as long as your function does not
1396 Now you need to set up the input code. The default for libpng is to
1397 use the C function fread(). If you use this, you will need to pass a
1398 valid FILE * in the function png_init_io(). Be sure that the file is
1399 opened in binary mode. If you wish to handle reading data in another
1400 way, you need not call the png_init_io() function, but you must then
1401 implement the libpng I/O methods discussed in the Customizing Libpng
1404 png_init_io(png_ptr, fp);
1406 If you had previously opened the file and read any of the signature from
1407 the beginning in order to see if this was a PNG file, you need to let
1408 libpng know that there are some bytes missing from the start of the file.
1410 png_set_sig_bytes(png_ptr, number);
1412 You can change the zlib compression buffer size to be used while
1413 reading compressed data with
1415 png_set_compression_buffer_size(png_ptr, buffer_size);
1417 where the default size is 8192 bytes. Note that the buffer size
1418 is changed immediately and the buffer is reallocated immediately,
1419 instead of setting a flag to be acted upon later.
1421 If you want CRC errors to be handled in a different manner than
1424 png_set_crc_action(png_ptr, crit_action, ancil_action);
1426 The values for png_set_crc_action() say how libpng is to handle CRC errors in
1427 ancillary and critical chunks, and whether to use the data contained
1428 therein. Note that it is impossible to "discard" data in a critical
1431 Choices for (int) crit_action are
1432 PNG_CRC_DEFAULT 0 error/quit
1433 PNG_CRC_ERROR_QUIT 1 error/quit
1434 PNG_CRC_WARN_USE 3 warn/use data
1435 PNG_CRC_QUIET_USE 4 quiet/use data
1436 PNG_CRC_NO_CHANGE 5 use the current value
1438 Choices for (int) ancil_action are
1439 PNG_CRC_DEFAULT 0 error/quit
1440 PNG_CRC_ERROR_QUIT 1 error/quit
1441 PNG_CRC_WARN_DISCARD 2 warn/discard data
1442 PNG_CRC_WARN_USE 3 warn/use data
1443 PNG_CRC_QUIET_USE 4 quiet/use data
1444 PNG_CRC_NO_CHANGE 5 use the current value
1446 .SS Setting up callback code
1448 You can set up a callback function to handle any unknown chunks in the
1449 input stream. You must supply the function
1451 read_chunk_callback(png_structp png_ptr,
1452 png_unknown_chunkp chunk);
1454 /* The unknown chunk structure contains your
1455 chunk data, along with similar data for any other
1462 /* Note that libpng has already taken care of
1465 /* put your code here. Search for your chunk in the
1466 unknown chunk structure, process it, and return one
1467 of the following: */
1469 return (-n); /* chunk had an error */
1470 return (0); /* did not recognize */
1471 return (n); /* success */
1474 (You can give your function another name that you like instead of
1475 "read_chunk_callback")
1477 To inform libpng about your function, use
1479 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1480 read_chunk_callback);
1482 This names not only the callback function, but also a user pointer that
1483 you can retrieve with
1485 png_get_user_chunk_ptr(png_ptr);
1487 If you call the png_set_read_user_chunk_fn() function, then all unknown
1488 chunks will be saved when read, in case your callback function will need
1489 one or more of them. This behavior can be changed with the
1490 png_set_keep_unknown_chunks() function, described below.
1492 At this point, you can set up a callback function that will be
1493 called after each row has been read, which you can use to control
1494 a progress meter or the like. It's demonstrated in pngtest.c.
1495 You must supply a function
1497 void read_row_callback(png_structp png_ptr,
1498 png_uint_32 row, int pass);
1500 /* put your code here */
1503 (You can give it another name that you like instead of "read_row_callback")
1505 To inform libpng about your function, use
1507 png_set_read_status_fn(png_ptr, read_row_callback);
1509 When this function is called the row has already been completely processed and
1510 the 'row' and 'pass' refer to the next row to be handled. For the
1511 non-interlaced case the row that was just handled is simply one less than the
1512 passed in row number, and pass will always be 0. For the interlaced case the
1513 same applies unless the row value is 0, in which case the row just handled was
1514 the last one from one of the preceding passes. Because interlacing may skip a
1515 pass you cannot be sure that the preceding pass is just 'pass-1', if you really
1516 need to know what the last pass is record (row,pass) from the callback and use
1517 the last recorded value each time.
1519 As with the user transform you can find the output row using the
1520 PNG_ROW_FROM_PASS_ROW macro.
1522 .SS Unknown-chunk handling
1524 Now you get to set the way the library processes unknown chunks in the
1525 input PNG stream. Both known and unknown chunks will be read. Normal
1526 behavior is that known chunks will be parsed into information in
1527 various info_ptr members while unknown chunks will be discarded. This
1528 behavior can be wasteful if your application will never use some known
1529 chunk types. To change this, you can call:
1531 png_set_keep_unknown_chunks(png_ptr, keep,
1532 chunk_list, num_chunks);
1533 keep - 0: default unknown chunk handling
1534 1: ignore; do not keep
1535 2: keep only if safe-to-copy
1536 3: keep even if unsafe-to-copy
1538 You can use these definitions:
1539 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1540 PNG_HANDLE_CHUNK_NEVER 1
1541 PNG_HANDLE_CHUNK_IF_SAFE 2
1542 PNG_HANDLE_CHUNK_ALWAYS 3
1544 chunk_list - list of chunks affected (a byte string,
1545 five bytes per chunk, NULL or '\0' if
1548 num_chunks - number of chunks affected; if 0, all
1549 unknown chunks are affected. If nonzero,
1550 only the chunks in the list are affected
1552 Unknown chunks declared in this way will be saved as raw data onto a
1553 list of png_unknown_chunk structures. If a chunk that is normally
1554 known to libpng is named in the list, it will be handled as unknown,
1555 according to the "keep" directive. If a chunk is named in successive
1556 instances of png_set_keep_unknown_chunks(), the final instance will
1557 take precedence. The IHDR and IEND chunks should not be named in
1558 chunk_list; if they are, libpng will process them normally anyway.
1559 If you know that your application will never make use of some particular
1560 chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below.
1562 Here is an example of the usage of png_set_keep_unknown_chunks(),
1563 where the private "vpAg" chunk will later be processed by a user chunk
1566 png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
1568 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1569 png_byte unused_chunks[]=
1571 104, 73, 83, 84, (png_byte) '\0', /* hIST */
1572 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
1573 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
1574 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
1575 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
1576 116, 73, 77, 69, (png_byte) '\0', /* tIME */
1582 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1583 /* ignore all unknown chunks: */
1584 png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
1586 /* except for vpAg: */
1587 png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
1589 /* also ignore unused known chunks: */
1590 png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
1591 (int)sizeof(unused_chunks)/5);
1596 The PNG specification allows the width and height of an image to be as
1597 large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1598 Since very few applications really need to process such large images,
1599 we have imposed an arbitrary 1-million limit on rows and columns.
1600 Larger images will be rejected immediately with a png_error() call. If
1601 you wish to change this limit, you can use
1603 png_set_user_limits(png_ptr, width_max, height_max);
1605 to set your own limits, or use width_max = height_max = 0x7fffffffL
1606 to allow all valid dimensions (libpng may reject some very large images
1607 anyway because of potential buffer overflow conditions).
1609 You should put this statement after you create the PNG structure and
1610 before calling png_read_info(), png_read_png(), or png_process_data().
1612 When writing a PNG datastream, put this statement before calling
1613 png_write_info() or png_write_png().
1615 If you need to retrieve the limits that are being applied, use
1617 width_max = png_get_user_width_max(png_ptr);
1618 height_max = png_get_user_height_max(png_ptr);
1620 The PNG specification sets no limit on the number of ancillary chunks
1621 allowed in a PNG datastream. You can impose a limit on the total number
1622 of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with
1624 png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
1626 where 0x7fffffffL means unlimited. You can retrieve this limit with
1628 chunk_cache_max = png_get_chunk_cache_max(png_ptr);
1630 This limit also applies to the number of buffers that can be allocated
1631 by png_decompress_chunk() while decompressing iTXt, zTXt, and iCCP chunks.
1633 You can also set a limit on the amount of memory that a compressed chunk
1634 other than IDAT can occupy, with
1636 png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
1638 and you can retrieve the limit with
1640 chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
1642 Any chunks that would cause either of these limits to be exceeded will
1645 .SS Information about your system
1647 If you intend to display the PNG or to incorporate it in other image data you
1648 need to tell libpng information about your display or drawing surface so that
1649 libpng can convert the values in the image to match the display.
1651 From libpng-1.5.4 this information can be set before reading the PNG file
1652 header. In earlier versions png_set_gamma() existed but behaved incorrectly if
1653 called before the PNG file header had been read and png_set_alpha_mode() did not
1656 If you need to support versions prior to libpng-1.5.4 test the version number
1657 as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures
1658 described in the appropriate manual page.
1660 You give libpng the encoding expected by your system expressed as a 'gamma'
1661 value. You can also specify a default encoding for the PNG file in
1662 case the required information is missing from the file. By default libpng
1663 assumes that the PNG data matches your system, to keep this default call:
1665 png_set_gamma(png_ptr, screen_gamma, 1/screen_gamma/*file gamma*/);
1667 or you can use the fixed point equivalent:
1669 png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma, PNG_FP_1/screen_gamma);
1671 If you don't know the gamma for your system it is probably 2.2 - a good
1672 approximation to the IEC standard for display systems (sRGB). If images are
1673 too contrasty or washed out you got the value wrong - check your system
1676 Many systems permit the system gamma to be changed via a lookup table in the
1677 display driver, a few systems, including older Macs, change the response by
1678 default. As of 1.5.4 three special values are available to handle common
1681 PNG_DEFAULT_sRGB: Indicates that the system conforms to the IEC 61966-2-1
1682 standard. This matches almost all systems.
1683 PNG_GAMMA_MAC_18: Indicates that the system is an older (pre Mac OS 10.6)
1684 Apple Macintosh system with the default settings.
1685 PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates that the
1686 system expects data with no gamma encoding.
1688 You would use the linear (unencoded) value if you need to process the pixel
1689 values further because this avoids the need to decode and reencode each
1690 component value whenever arithmetic is performed. A lot of graphics software
1691 uses linear values for this reason, often with higher precision component values
1692 to preserve overall accuracy.
1694 The second thing you may need to tell libpng about is how your system handles
1695 alpha channel information. Some, but not all, PNG files contain an alpha
1696 channel. To display these files correctly you need to compose the data onto a
1697 suitable background, as described in the PNG specification.
1699 Libpng only supports composing onto a single color (using png_set_background;
1700 see below). Otherwise you must do the composition yourself and, in this case,
1701 you may need to call png_set_alpha_mode:
1703 #if PNG_LIBPNG_VER >= 10504
1704 png_set_alpha_mode(png_ptr, mode, screen_gamma);
1706 png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma);
1709 The screen_gamma value is the same as the argument to png_set_gamma; however,
1710 how it affects the output depends on the mode. png_set_alpha_mode() sets the
1711 file gamma default to 1/screen_gamma, so normally you don't need to call
1712 png_set_gamma. If you need different defaults call png_set_gamma() before
1713 png_set_alpha_mode() - if you call it after it will override the settings made
1714 by png_set_alpha_mode().
1716 The mode is as follows:
1718 PNG_ALPHA_PNG: The data is encoded according to the PNG specification. Red,
1719 green and blue, or gray, components are gamma encoded color
1720 values and are not premultiplied by the alpha value. The
1721 alpha value is a linear measure of the contribution of the
1722 pixel to the corresponding final output pixel.
1724 You should normally use this format if you intend to perform
1725 color correction on the color values; most, maybe all, color
1726 correction software has no handling for the alpha channel and,
1727 anyway, the math to handle pre-multiplied component values is
1728 unnecessarily complex.
1730 Before you do any arithmetic on the component values you need
1731 to remove the gamma encoding and multiply out the alpha
1732 channel. See the PNG specification for more detail. It is
1733 important to note that when an image with an alpha channel is
1734 scaled, linear encoded, pre-multiplied component values must
1737 The remaining modes assume you don't need to do any further color correction or
1738 that if you do, your color correction software knows all about alpha (it
1741 PNG_ALPHA_STANDARD: The data libpng produces
1742 is encoded in the standard way
1743 assumed by most correctly written graphics software.
1744 The gamma encoding will be removed by libpng and the
1745 linear component values will be pre-multiplied by the
1748 With this format the final image must be re-encoded to
1749 match the display gamma before the image is displayed.
1750 If your system doesn't do that, yet still seems to
1751 perform arithmetic on the pixels without decoding them,
1752 it is broken - check out the modes below.
1754 With PNG_ALPHA_STANDARD libpng always produces linear
1755 component values, whatever screen_gamma you supply. The
1756 screen_gamma value is, however, used as a default for
1757 the file gamma if the PNG file has no gamma information.
1759 If you call png_set_gamma() after png_set_alpha_mode() you
1760 will override the linear encoding. Instead the
1761 pre-multiplied pixel values will be gamma encoded but
1762 the alpha channel will still be linear. This may
1763 actually match the requirements of some broken software,
1766 While linear 8-bit data is often used it has
1767 insufficient precision for any image with a reasonable
1768 dynamic range. To avoid problems, and if your software
1769 supports it, use png_set_expand_16() to force all
1770 components to 16 bits.
1772 PNG_ALPHA_OPTIMIZED: This mode is the same
1773 as PNG_ALPHA_STANDARD except that
1774 completely opaque pixels are gamma encoded according to
1775 the screen_gamma value. Pixels with alpha less than 1.0
1776 will still have linear components.
1778 Use this format if you have control over your
1779 compositing software and do don't do other arithmetic
1780 (such as scaling) on the data you get from libpng. Your
1781 compositing software can simply copy opaque pixels to
1782 the output but still has linear values for the
1785 In normal compositing, where the alpha channel encodes
1786 partial pixel coverage (as opposed to broad area
1787 translucency), the inaccuracies of the 8-bit
1788 representation of non-opaque pixels are irrelevant.
1790 You can also try this format if your software is broken;
1791 it might look better.
1793 PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD;
1794 however, all component values,
1795 including the alpha channel are gamma encoded. This is
1796 an appropriate format to try if your software, or more
1797 likely hardware, is totally broken, i.e., if it performs
1798 linear arithmetic directly on gamma encoded values.
1800 In most cases of broken software or hardware the bug in the final display
1801 manifests as a subtle halo around composited parts of the image. You may not
1802 even perceive this as a halo; the composited part of the image may simply appear
1803 separate from the background, as though it had been cut out of paper and pasted
1806 If you don't have to deal with bugs in software or hardware, or if you can fix
1807 them, there are three recommended ways of using png_set_alpha_mode():
1809 png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG,
1812 You can do color correction on the result (libpng does not currently
1813 support color correction internally). When you handle the alpha channel
1814 you need to undo the gamma encoding and multiply out the alpha.
1816 png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD,
1818 png_set_expand_16(png_ptr);
1820 If you are using the high level interface, don't call png_set_expand_16();
1821 instead pass PNG_TRANSFORM_EXPAND_16 to the interface.
1823 With this mode you can't do color correction, but you can do arithmetic,
1824 including composition and scaling, on the data without further processing.
1826 png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED,
1829 You can avoid the expansion to 16-bit components with this mode, but you
1830 lose the ability to scale the image or perform other linear arithmetic.
1831 All you can do is compose the result onto a matching output. Since this
1832 mode is libpng-specific you also need to write your own composition
1835 If you don't need, or can't handle, the alpha channel you can call
1836 png_set_background() to remove it by compositing against a fixed color. Don't
1837 call png_set_strip_alpha() to do this - it will leave spurious pixel values in
1838 transparent parts of this image.
1840 png_set_background(png_ptr, &background_color,
1841 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1);
1843 The background_color is an RGB or grayscale value according to the data format
1844 libpng will produce for you. Because you don't yet know the format of the PNG
1845 file, if you call png_set_background at this point you must arrange for the
1846 format produced by libpng to always have 8-bit or 16-bit components and then
1847 store the color as an 8-bit or 16-bit color as appropriate. The color contains
1848 separate gray and RGB component values, so you can let libpng produce gray or
1849 RGB output according to the input format, but low bit depth grayscale images
1850 must always be converted to at least 8-bit format. (Even though low bit depth
1851 grayscale images can't have an alpha channel they can have a transparent
1854 You set the transforms you need later, either as flags to the high level
1855 interface or libpng API calls for the low level interface. For reference the
1856 settings and API calls required are:
1859 PNG_TRANSFORM_SCALE_16 | PNG_EXPAND
1860 png_set_expand(png_ptr); png_set_scale_16(png_ptr);
1862 If you must get exactly the same inaccurate results
1863 produced by default in versions prior to libpng-1.5.4,
1864 use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr)
1868 PNG_TRANSFORM_EXPAND_16
1869 png_set_expand_16(png_ptr);
1871 In either case palette image data will be expanded to RGB. If you just want
1872 color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr)
1875 Calling png_set_background before the PNG file header is read will not work
1876 prior to libpng-1.5.4. Because the failure may result in unexpected warnings or
1877 errors it is therefore much safer to call png_set_background after the head has
1878 been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be
1879 used with the high level interface.
1881 .SS The high-level read interface
1883 At this point there are two ways to proceed; through the high-level
1884 read interface, or through a sequence of low-level read operations.
1885 You can use the high-level interface if (a) you are willing to read
1886 the entire image into memory, and (b) the input transformations
1887 you want to do are limited to the following set:
1889 PNG_TRANSFORM_IDENTITY No transformation
1890 PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to
1892 PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to
1893 8-bit less accurately
1894 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1895 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1897 PNG_TRANSFORM_PACKSWAP Change order of packed
1899 PNG_TRANSFORM_EXPAND Perform set_expand()
1900 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1901 PNG_TRANSFORM_SHIFT Normalize pixels to the
1903 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1905 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1907 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1909 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1910 PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
1911 to RGB (or GA to RGBA)
1912 PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits
1914 (This excludes setting a background color, doing gamma transformation,
1915 quantizing, and setting filler.) If this is the case, simply do this:
1917 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1919 where png_transforms is an integer containing the bitwise OR of some
1920 set of transformation flags. This call is equivalent to png_read_info(),
1921 followed the set of transformations indicated by the transform mask,
1922 then png_read_image(), and finally png_read_end().
1924 (The final parameter of this call is not yet used. Someday it might point
1925 to transformation parameters required by some future input transform.)
1927 You must use png_transforms and not call any png_set_transform() functions
1928 when you use png_read_png().
1930 After you have called png_read_png(), you can retrieve the image data
1933 row_pointers = png_get_rows(png_ptr, info_ptr);
1935 where row_pointers is an array of pointers to the pixel data for each row:
1937 png_bytep row_pointers[height];
1939 If you know your image size and pixel size ahead of time, you can allocate
1940 row_pointers prior to calling png_read_png() with
1942 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1944 "Image is too tall to process in memory");
1946 if (width > PNG_UINT_32_MAX/pixel_size)
1948 "Image is too wide to process in memory");
1950 row_pointers = png_malloc(png_ptr,
1951 height*png_sizeof(png_bytep));
1953 for (int i=0; i<height, i++)
1954 row_pointers[i]=NULL; /* security precaution */
1956 for (int i=0; i<height, i++)
1957 row_pointers[i]=png_malloc(png_ptr,
1960 png_set_rows(png_ptr, info_ptr, &row_pointers);
1962 Alternatively you could allocate your image in one big block and define
1963 row_pointers[i] to point into the proper places in your block.
1965 If you use png_set_rows(), the application is responsible for freeing
1966 row_pointers (and row_pointers[i], if they were separately allocated).
1968 If you don't allocate row_pointers ahead of time, png_read_png() will
1969 do it, and it'll be free'ed by libpng when you call png_destroy_*().
1971 .SS The low-level read interface
1973 If you are going the low-level route, you are now ready to read all
1974 the file information up to the actual image data. You do this with a
1975 call to png_read_info().
1977 png_read_info(png_ptr, info_ptr);
1979 This will process all chunks up to but not including the image data.
1981 This also copies some of the data from the PNG file into the decode structure
1982 for use in later transformations. Important information copied in is:
1984 1) The PNG file gamma from the gAMA chunk. This overwrites the default value
1985 provided by an earlier call to png_set_gamma or png_set_alpha_mode.
1987 2) Prior to libpng-1.5.4 the background color from a bKGd chunk. This
1988 damages the information provided by an earlier call to png_set_background
1989 resulting in unexpected behavior. Libpng-1.5.4 no longer does this.
1991 3) The number of significant bits in each component value. Libpng uses this to
1992 optimize gamma handling by reducing the internal lookup table sizes.
1994 4) The transparent color information from a tRNS chunk. This can be modified by
1995 a later call to png_set_tRNS.
1997 .SS Querying the info structure
1999 Functions are used to get the information from the info_ptr once it
2000 has been read. Note that these fields may not be completely filled
2001 in until png_read_end() has read the chunk data following the image.
2003 png_get_IHDR(png_ptr, info_ptr, &width, &height,
2004 &bit_depth, &color_type, &interlace_type,
2005 &compression_type, &filter_method);
2007 width - holds the width of the image
2008 in pixels (up to 2^31).
2010 height - holds the height of the image
2011 in pixels (up to 2^31).
2013 bit_depth - holds the bit depth of one of the
2014 image channels. (valid values are
2015 1, 2, 4, 8, 16 and depend also on
2016 the color_type. See also
2017 significant bits (sBIT) below).
2019 color_type - describes which color/alpha channels
2022 (bit depths 1, 2, 4, 8, 16)
2023 PNG_COLOR_TYPE_GRAY_ALPHA
2025 PNG_COLOR_TYPE_PALETTE
2026 (bit depths 1, 2, 4, 8)
2029 PNG_COLOR_TYPE_RGB_ALPHA
2032 PNG_COLOR_MASK_PALETTE
2033 PNG_COLOR_MASK_COLOR
2034 PNG_COLOR_MASK_ALPHA
2036 interlace_type - (PNG_INTERLACE_NONE or
2037 PNG_INTERLACE_ADAM7)
2039 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
2042 filter_method - (must be PNG_FILTER_TYPE_BASE
2043 for PNG 1.0, and can also be
2044 PNG_INTRAPIXEL_DIFFERENCING if
2045 the PNG datastream is embedded in
2046 a MNG-1.0 datastream)
2048 Any or all of interlace_type, compression_type, or
2049 filter_method can be NULL if you are
2050 not interested in their values.
2052 Note that png_get_IHDR() returns 32-bit data into
2053 the application's width and height variables.
2054 This is an unsafe situation if these are 16-bit
2055 variables. In such situations, the
2056 png_get_image_width() and png_get_image_height()
2057 functions described below are safer.
2059 width = png_get_image_width(png_ptr,
2062 height = png_get_image_height(png_ptr,
2065 bit_depth = png_get_bit_depth(png_ptr,
2068 color_type = png_get_color_type(png_ptr,
2071 interlace_type = png_get_interlace_type(png_ptr,
2074 compression_type = png_get_compression_type(png_ptr,
2077 filter_method = png_get_filter_type(png_ptr,
2080 channels = png_get_channels(png_ptr, info_ptr);
2082 channels - number of channels of info for the
2083 color type (valid values are 1 (GRAY,
2084 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
2085 4 (RGB_ALPHA or RGB + filler byte))
2087 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
2089 rowbytes - number of bytes needed to hold a row
2091 signature = png_get_signature(png_ptr, info_ptr);
2093 signature - holds the signature read from the
2094 file (if any). The data is kept in
2095 the same offset it would be if the
2096 whole signature were read (i.e. if an
2097 application had already read in 4
2098 bytes of signature before starting
2099 libpng, the remaining 4 bytes would
2100 be in signature[4] through signature[7]
2101 (see png_set_sig_bytes())).
2103 These are also important, but their validity depends on whether the chunk
2104 has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
2105 png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
2106 data has been read, or zero if it is missing. The parameters to the
2107 png_get_<chunk> are set directly if they are simple data types, or a
2108 pointer into the info_ptr is returned for any complex types.
2110 png_get_PLTE(png_ptr, info_ptr, &palette,
2113 palette - the palette for the file
2114 (array of png_color)
2116 num_palette - number of entries in the palette
2118 png_get_gAMA(png_ptr, info_ptr, &file_gamma);
2119 png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma);
2121 file_gamma - the gamma at which the file is
2122 written (PNG_INFO_gAMA)
2124 int_file_gamma - 100,000 times the gamma at which the
2127 png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x, &red_y,
2128 &green_x, &green_y, &blue_x, &blue_y)
2129 png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z, &green_X,
2130 &green_Y, &green_Z, &blue_X, &blue_Y, &blue_Z)
2131 png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x, &int_white_y,
2132 &int_red_x, &int_red_y, &int_green_x, &int_green_y,
2133 &int_blue_x, &int_blue_y)
2134 png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y,
2135 &int_red_Z, &int_green_X, &int_green_Y, &int_green_Z,
2136 &int_blue_X, &int_blue_Y, &int_blue_Z)
2138 {white,red,green,blue}_{x,y}
2139 A color space encoding specified using the chromaticities
2140 of the end points and the white point. (PNG_INFO_cHRM)
2142 {red,green,blue}_{X,Y,Z}
2143 A color space encoding specified using the encoding end
2144 points - the CIE tristimulus specification of the intended
2145 color of the red, green and blue channels in the PNG RGB
2146 data. The white point is simply the sum of the three end
2147 points. (PNG_INFO_cHRM)
2149 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
2151 file_srgb_intent - the rendering intent (PNG_INFO_sRGB)
2152 The presence of the sRGB chunk
2153 means that the pixel data is in the
2154 sRGB color space. This chunk also
2155 implies specific values of gAMA and
2158 png_get_iCCP(png_ptr, info_ptr, &name,
2159 &compression_type, &profile, &proflen);
2161 name - The profile name.
2163 compression_type - The compression type; always
2164 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2165 You may give NULL to this argument to
2168 profile - International Color Consortium color
2169 profile data. May contain NULs.
2171 proflen - length of profile data in bytes.
2173 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
2175 sig_bit - the number of significant bits for
2176 (PNG_INFO_sBIT) each of the gray,
2177 red, green, and blue channels,
2178 whichever are appropriate for the
2179 given color type (png_color_16)
2181 png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
2182 &num_trans, &trans_color);
2184 trans_alpha - array of alpha (transparency)
2185 entries for palette (PNG_INFO_tRNS)
2187 num_trans - number of transparent entries
2190 trans_color - graylevel or color sample values of
2191 the single transparent color for
2192 non-paletted images (PNG_INFO_tRNS)
2194 png_get_hIST(png_ptr, info_ptr, &hist);
2197 hist - histogram of palette (array of
2200 png_get_tIME(png_ptr, info_ptr, &mod_time);
2202 mod_time - time image was last modified
2205 png_get_bKGD(png_ptr, info_ptr, &background);
2207 background - background color (of type
2208 png_color_16p) (PNG_VALID_bKGD)
2209 valid 16-bit red, green and blue
2210 values, regardless of color_type
2212 num_comments = png_get_text(png_ptr, info_ptr,
2213 &text_ptr, &num_text);
2215 num_comments - number of comments
2217 text_ptr - array of png_text holding image
2220 text_ptr[i].compression - type of compression used
2221 on "text" PNG_TEXT_COMPRESSION_NONE
2222 PNG_TEXT_COMPRESSION_zTXt
2223 PNG_ITXT_COMPRESSION_NONE
2224 PNG_ITXT_COMPRESSION_zTXt
2226 text_ptr[i].key - keyword for comment. Must contain
2229 text_ptr[i].text - text comments for current
2230 keyword. Can be empty.
2232 text_ptr[i].text_length - length of text string,
2233 after decompression, 0 for iTXt
2235 text_ptr[i].itxt_length - length of itxt string,
2236 after decompression, 0 for tEXt/zTXt
2238 text_ptr[i].lang - language of comment (empty
2239 string for unknown).
2241 text_ptr[i].lang_key - keyword in UTF-8
2242 (empty string for unknown).
2244 Note that the itxt_length, lang, and lang_key
2245 members of the text_ptr structure only exist
2246 when the library is built with iTXt chunk support.
2247 Prior to libpng-1.4.0, the default build was
2248 without iTXt chunk support.
2250 num_text - number of comments (same as
2251 num_comments; you can put NULL here
2252 to avoid the duplication)
2254 Note while png_set_text() will accept text, language,
2255 and translated keywords that can be NULL pointers, the
2256 structure returned by png_get_text will always contain
2257 regular zero-terminated C strings. They might be
2258 empty strings but they will never be NULL pointers.
2260 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
2263 num_spalettes - number of sPLT chunks read.
2265 palette_ptr - array of palette structures holding
2266 contents of one or more sPLT chunks
2269 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
2272 offset_x - positive offset from the left edge
2273 of the screen (can be negative)
2275 offset_y - positive offset from the top edge
2276 of the screen (can be negative)
2278 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2280 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
2283 res_x - pixels/unit physical resolution in
2286 res_y - pixels/unit physical resolution in
2289 unit_type - PNG_RESOLUTION_UNKNOWN,
2290 PNG_RESOLUTION_METER
2292 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
2295 unit - physical scale units (an integer)
2297 width - width of a pixel in physical scale units
2299 height - height of a pixel in physical scale units
2300 (width and height are doubles)
2302 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
2305 unit - physical scale units (an integer)
2307 width - width of a pixel in physical scale units
2308 (expressed as a string)
2310 height - height of a pixel in physical scale units
2311 (width and height are strings like "2.54")
2313 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
2314 info_ptr, &unknowns)
2316 unknowns - array of png_unknown_chunk
2317 structures holding unknown chunks
2319 unknowns[i].name - name of unknown chunk
2321 unknowns[i].data - data of unknown chunk
2323 unknowns[i].size - size of unknown chunk's data
2325 unknowns[i].location - position of chunk in file
2327 The value of "i" corresponds to the order in which the
2328 chunks were read from the PNG file or inserted with the
2329 png_set_unknown_chunks() function.
2331 The value of "location" is a bitwise "or" of
2333 PNG_HAVE_IHDR (0x01)
2334 PNG_HAVE_PLTE (0x02)
2335 PNG_AFTER_IDAT (0x08)
2337 The data from the pHYs chunk can be retrieved in several convenient
2340 res_x = png_get_x_pixels_per_meter(png_ptr,
2343 res_y = png_get_y_pixels_per_meter(png_ptr,
2346 res_x_and_y = png_get_pixels_per_meter(png_ptr,
2349 res_x = png_get_x_pixels_per_inch(png_ptr,
2352 res_y = png_get_y_pixels_per_inch(png_ptr,
2355 res_x_and_y = png_get_pixels_per_inch(png_ptr,
2358 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
2361 Each of these returns 0 [signifying "unknown"] if
2362 the data is not present or if res_x is 0;
2363 res_x_and_y is 0 if res_x != res_y
2365 Note that because of the way the resolutions are
2366 stored internally, the inch conversions won't
2367 come out to exactly even number. For example,
2368 72 dpi is stored as 0.28346 pixels/meter, and
2369 when this is retrieved it is 71.9988 dpi, so
2370 be sure to round the returned value appropriately
2371 if you want to display a reasonable-looking result.
2373 The data from the oFFs chunk can be retrieved in several convenient
2376 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
2378 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
2380 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
2382 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
2384 Each of these returns 0 [signifying "unknown" if both
2385 x and y are 0] if the data is not present or if the
2386 chunk is present but the unit is the pixel. The
2387 remark about inexact inch conversions applies here
2388 as well, because a value in inches can't always be
2389 converted to microns and back without some loss
2392 For more information, see the
2393 PNG specification for chunk contents. Be careful with trusting
2394 rowbytes, as some of the transformations could increase the space
2395 needed to hold a row (expand, filler, gray_to_rgb, etc.).
2396 See png_read_update_info(), below.
2398 A quick word about text_ptr and num_text. PNG stores comments in
2399 keyword/text pairs, one pair per chunk, with no limit on the number
2400 of text chunks, and a 2^31 byte limit on their size. While there are
2401 suggested keywords, there is no requirement to restrict the use to these
2402 strings. It is strongly suggested that keywords and text be sensible
2403 to humans (that's the point), so don't use abbreviations. Non-printing
2404 symbols are not allowed. See the PNG specification for more details.
2405 There is also no requirement to have text after the keyword.
2407 Keywords should be limited to 79 Latin-1 characters without leading or
2408 trailing spaces, but non-consecutive spaces are allowed within the
2409 keyword. It is possible to have the same keyword any number of times.
2410 The text_ptr is an array of png_text structures, each holding a
2411 pointer to a language string, a pointer to a keyword and a pointer to
2412 a text string. The text string, language code, and translated
2413 keyword may be empty or NULL pointers. The keyword/text
2414 pairs are put into the array in the order that they are received.
2415 However, some or all of the text chunks may be after the image, so, to
2416 make sure you have read all the text chunks, don't mess with these
2417 until after you read the stuff after the image. This will be
2418 mentioned again below in the discussion that goes with png_read_end().
2420 .SS Input transformations
2422 After you've read the header information, you can set up the library
2423 to handle any special transformations of the image data. The various
2424 ways to transform the data will be described in the order that they
2425 should occur. This is important, as some of these change the color
2426 type and/or bit depth of the data, and some others only work on
2427 certain color types and bit depths.
2429 Transformations you request are ignored if they don't have any meaning for a
2430 particular input data format. However some transformations can have an effect
2431 as a result of a previous transformation. If you specify a contradictory set of
2432 transformations, for example both adding and removing the alpha channel, you
2433 cannot predict the final result.
2435 The color used for the transparency values should be supplied in the same
2436 format/depth as the current image data. It is stored in the same format/depth
2437 as the image data in a tRNS chunk, so this is what libpng expects for this data.
2439 The color used for the background value depends on the need_expand argument as
2442 Data will be decoded into the supplied row buffers packed into bytes
2443 unless the library has been told to transform it into another format.
2444 For example, 4 bit/pixel paletted or grayscale data will be returned
2445 2 pixels/byte with the leftmost pixel in the high-order bits of the
2446 byte, unless png_set_packing() is called. 8-bit RGB data will be stored
2447 in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
2448 is called to insert filler bytes, either before or after each RGB triplet.
2449 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
2450 byte of the color value first, unless png_set_scale_16() is called to
2451 transform it to regular RGB RGB triplets, or png_set_filler() or
2452 png_set_add alpha() is called to insert filler bytes, either before or
2453 after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
2454 be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(),
2455 or png_set_scale_16().
2457 The following code transforms grayscale images of less than 8 to 8 bits,
2458 changes paletted images to RGB, and adds a full alpha channel if there is
2459 transparency information in a tRNS chunk. This is most useful on
2460 grayscale images with bit depths of 2 or 4 or if there is a multiple-image
2461 viewing application that wishes to treat all images in the same way.
2463 if (color_type == PNG_COLOR_TYPE_PALETTE)
2464 png_set_palette_to_rgb(png_ptr);
2466 if (png_get_valid(png_ptr, info_ptr,
2467 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
2469 if (color_type == PNG_COLOR_TYPE_GRAY &&
2470 bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
2472 The first two functions are actually aliases for png_set_expand(), added
2473 in libpng version 1.0.4, with the function names expanded to improve code
2474 readability. In some future version they may actually do different
2477 As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
2478 added. It expands the sample depth without changing tRNS to alpha.
2480 As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as
2481 png_set_expand(); however, the resultant channels have 16 bits rather than 8.
2482 Use this when the output color or gray channels are made linear to avoid fairly
2483 severe accuracy loss.
2486 png_set_expand_16(png_ptr);
2488 PNG can have files with 16 bits per channel. If you only can handle
2489 8 bits per channel, this will strip the pixels down to 8-bit.
2491 if (bit_depth == 16)
2492 #if PNG_LIBPNG_VER >= 10504
2493 png_set_scale_16(png_ptr);
2495 png_set_strip_16(png_ptr);
2498 (The more accurate "png_set_scale_16()" API became available in libpng version
2501 If you need to process the alpha channel on the image separately from the image
2502 data (for example if you convert it to a bitmap mask) it is possible to have
2503 libpng strip the channel leaving just RGB or gray data:
2505 if (color_type & PNG_COLOR_MASK_ALPHA)
2506 png_set_strip_alpha(png_ptr);
2508 If you strip the alpha channel you need to find some other way of dealing with
2509 the information. If, instead, you want to convert the image to an opaque
2510 version with no alpha channel use png_set_background; see below.
2512 As of libpng version 1.5.2, almost all useful expansions are supported, the
2513 major ommissions are conversion of grayscale to indexed images (which can be
2514 done trivially in the application) and conversion of indexed to grayscale (which
2515 can be done by a trivial manipulation of the palette.)
2517 In the following table, the 01 means grayscale with depth<8, 31 means
2518 indexed with depth<8, other numerals represent the color type, "T" means
2519 the tRNS chunk is present, A means an alpha channel is present, and O
2520 means tRNS or alpha is present but all pixels in the image are opaque.
2522 FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
2524 01 - [G] - - - - - - - - - - - - -
2525 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q
2526 0 1 G + . . G G G G G G B B GB GB
2527 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt
2528 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt
2529 2 C P C C C + . . C - - CB CB B B
2530 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt
2531 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt
2532 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q
2533 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt
2534 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt
2535 4A lA G A T T GA GT GT GA GT GT + BA G GBA
2536 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G
2537 6A CA PA CA C C A T tT PA P P C CBA + BA
2538 6O CA PBA CA C C A tT T PA P P CBA C BA +
2541 "+" identifies entries where 'from' and 'to' are the same.
2542 "-" means the transformation is not supported.
2543 "." means nothing is necessary (a tRNS chunk can just be ignored).
2544 "t" means the transformation is obtained by png_set_tRNS.
2545 "A" means the transformation is obtained by png_set_add_alpha().
2546 "X" means the transformation is obtained by png_set_expand().
2547 "1" means the transformation is obtained by
2548 png_set_expand_gray_1_2_4_to_8() (and by png_set_expand() if there
2549 is no transparency in the original or the final format).
2550 "C" means the transformation is obtained by png_set_gray_to_rgb().
2551 "G" means the transformation is obtained by png_set_rgb_to_gray().
2552 "P" means the transformation is obtained by
2553 png_set_expand_palette_to_rgb().
2554 "p" means the transformation is obtained by png_set_packing().
2555 "Q" means the transformation is obtained by png_set_quantize().
2556 "T" means the transformation is obtained by png_set_tRNS_to_alpha().
2557 "B" means the transformation is obtained by png_set_background(), or
2560 When an entry has multiple transforms listed all are required to cause the
2561 right overall transformation. When two transforms are separated by a comma
2562 either will do the job. When transforms are enclosed in [] the transform should
2563 do the job but this is currently unimplemented - a different format will result
2564 if the suggested transformations are used.
2566 In PNG files, the alpha channel in an image
2567 is the level of opacity. If you need the alpha channel in an image to
2568 be the level of transparency instead of opacity, you can invert the
2569 alpha channel (or the tRNS chunk data) after it's read, so that 0 is
2570 fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
2571 images) is fully transparent, with
2573 png_set_invert_alpha(png_ptr);
2575 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2576 they can, resulting in, for example, 8 pixels per byte for 1 bit
2577 files. This code expands to 1 pixel per byte without changing the
2578 values of the pixels:
2581 png_set_packing(png_ptr);
2583 PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
2584 stored in a PNG image have been "scaled" or "shifted" up to the next
2585 higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
2586 to 8 bits/sample in the range [0, 255]). However, it is also possible
2587 to convert the PNG pixel data back to the original bit depth of the
2588 image. This call reduces the pixels back down to the original bit depth:
2590 png_color_8p sig_bit;
2592 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
2593 png_set_shift(png_ptr, sig_bit);
2595 PNG files store 3-color pixels in red, green, blue order. This code
2596 changes the storage of the pixels to blue, green, red:
2598 if (color_type == PNG_COLOR_TYPE_RGB ||
2599 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2600 png_set_bgr(png_ptr);
2602 PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
2603 into 4 or 8 bytes for windowing systems that need them in this format:
2605 if (color_type == PNG_COLOR_TYPE_RGB)
2606 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
2608 where "filler" is the 8 or 16-bit number to fill with, and the location is
2609 either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
2610 you want the filler before the RGB or after. This transformation
2611 does not affect images that already have full alpha channels. To add an
2612 opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
2613 will generate RGBA pixels.
2615 Note that png_set_filler() does not change the color type. If you want
2616 to do that, you can add a true alpha channel with
2618 if (color_type == PNG_COLOR_TYPE_RGB ||
2619 color_type == PNG_COLOR_TYPE_GRAY)
2620 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
2622 where "filler" contains the alpha value to assign to each pixel.
2623 This function was added in libpng-1.2.7.
2625 If you are reading an image with an alpha channel, and you need the
2626 data as ARGB instead of the normal PNG format RGBA:
2628 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2629 png_set_swap_alpha(png_ptr);
2631 For some uses, you may want a grayscale image to be represented as
2632 RGB. This code will do that conversion:
2634 if (color_type == PNG_COLOR_TYPE_GRAY ||
2635 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2636 png_set_gray_to_rgb(png_ptr);
2638 Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
2641 if (color_type == PNG_COLOR_TYPE_RGB ||
2642 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2643 png_set_rgb_to_gray(png_ptr, error_action, double red_weight,
2644 double green_weight);
2646 error_action = 1: silently do the conversion
2648 error_action = 2: issue a warning if the original
2649 image has any pixel where
2650 red != green or red != blue
2652 error_action = 3: issue an error and abort the
2653 conversion if the original
2654 image has any pixel where
2655 red != green or red != blue
2657 red_weight: weight of red component
2659 green_weight: weight of green component
2660 If either weight is negative, default
2663 In the corresponding fixed point API the red_weight and green_weight values are
2664 simply scaled by 100,000:
2666 png_set_rgb_to_gray(png_ptr, error_action, png_fixed_point red_weight,
2667 png_fixed_point green_weight);
2669 If you have set error_action = 1 or 2, you can
2670 later check whether the image really was gray, after processing
2671 the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
2672 It will return a png_byte that is zero if the image was gray or
2673 1 if there were any non-gray pixels. Background and sBIT data
2674 will be silently converted to grayscale, using the green channel
2675 data for sBIT, regardless of the error_action setting.
2677 The default values come from the PNG file cHRM chunk if present; otherwise, the
2678 defaults correspond to the ITU-R recommendation 709, and also the sRGB color
2679 space, as recommended in the Charles Poynton's Colour FAQ,
2680 <http://www.poynton.com/>, in section 9:
2682 <http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9>
2684 Y = 0.2126 * R + 0.7152 * G + 0.0722 * B
2686 Previous versions of this document, 1998 through 2002, recommended a slightly
2689 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
2691 Libpng uses an integer approximation:
2693 Y = (6968 * R + 23434 * G + 2366 * B)/32768
2695 The calculation is done in a linear colorspace, if the image gamma
2698 The png_set_background() function has been described already; it tells libpng to
2699 composite images with alpha or simple transparency against the supplied
2700 background color. For compatibility with versions of libpng earlier than
2701 libpng-1.5.4 it is recommended that you call the function after reading the file
2702 header, even if you don't want to use the color in a bKGD chunk, if one exists.
2704 If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
2705 you may use this color, or supply another color more suitable for
2706 the current display (e.g., the background color from a web page). You
2707 need to tell libpng how the color is represented, both the format of the
2708 component values in the color (the number of bits) and the gamma encoding of the
2709 color. The function takes two arguments, background_gamma_mode and need_expand
2710 to convey this information, however only two combinations are likely to be
2713 png_color_16 my_background;
2714 png_color_16p image_background;
2716 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
2717 png_set_background(png_ptr, image_background,
2718 PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1);
2720 png_set_background(png_ptr, &my_background,
2721 PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1);
2723 The second call was described above - my_background is in the format of the
2724 final, display, output produced by libpng. Because you now know the format of
2725 the PNG it is possible to avoid the need to choose either 8-bit or 16-bit
2726 output and to retain palette images (the palette colors will be modified
2727 appropriately and the tRNS chunk removed.) However, if you are doing this,
2728 take great care not to ask for transformations without checking first that
2731 In the first call the background color has the original bit depth and color type
2732 of the PNG file. So, for palette images the color is supplied as a palette
2733 index and for low bit greyscale images the color is a reduced bit value in
2734 image_background->gray.
2736 If you didn't call png_set_gamma() before reading the file header, for example
2737 if you need your code to remain compatible with older versions of libpng prior
2738 to libpng-1.5.4, this is the place to call it.
2740 Do not call it if you called png_set_alpha_mode(); doing so will damage the
2741 settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is
2742 supported then you can certainly do png_set_gamma() before reading the PNG
2745 This API unconditionally sets the screen and file gamma values, so it will
2746 override the value in the PNG file unless it is called before the PNG file
2747 reading starts. For this reason you must always call it with the PNG file
2748 value when you call it in this position:
2750 if (png_get_gAMA(png_ptr, info_ptr, &file_gamma))
2751 png_set_gamma(png_ptr, screen_gamma, file_gamma);
2754 png_set_gamma(png_ptr, screen_gamma, 0.45455);
2756 If you need to reduce an RGB file to a paletted file, or if a paletted
2757 file has more entries then will fit on your screen, png_set_quantize()
2758 will do that. Note that this is a simple match quantization that merely
2759 finds the closest color available. This should work fairly well with
2760 optimized palettes, but fairly badly with linear color cubes. If you
2761 pass a palette that is larger than maximum_colors, the file will
2762 reduce the number of colors in the palette so it will fit into
2763 maximum_colors. If there is a histogram, libpng will use it to make
2764 more intelligent choices when reducing the palette. If there is no
2765 histogram, it may not do as good a job.
2767 if (color_type & PNG_COLOR_MASK_COLOR)
2769 if (png_get_valid(png_ptr, info_ptr,
2772 png_uint_16p histogram = NULL;
2774 png_get_hIST(png_ptr, info_ptr,
2776 png_set_quantize(png_ptr, palette, num_palette,
2777 max_screen_colors, histogram, 1);
2782 png_color std_color_cube[MAX_SCREEN_COLORS] =
2785 png_set_quantize(png_ptr, std_color_cube,
2786 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
2791 PNG files describe monochrome as black being zero and white being one.
2792 The following code will reverse this (make black be one and white be
2795 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
2796 png_set_invert_mono(png_ptr);
2798 This function can also be used to invert grayscale and gray-alpha images:
2800 if (color_type == PNG_COLOR_TYPE_GRAY ||
2801 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2802 png_set_invert_mono(png_ptr);
2804 PNG files store 16-bit pixels in network byte order (big-endian,
2805 ie. most significant bits first). This code changes the storage to the
2806 other way (little-endian, i.e. least significant bits first, the
2807 way PCs store them):
2809 if (bit_depth == 16)
2810 png_set_swap(png_ptr);
2812 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2813 need to change the order the pixels are packed into bytes, you can use:
2816 png_set_packswap(png_ptr);
2818 Finally, you can write your own transformation function if none of
2819 the existing ones meets your needs. This is done by setting a callback
2822 png_set_read_user_transform_fn(png_ptr,
2825 You must supply the function
2827 void read_transform_fn(png_structp png_ptr, png_row_infop
2828 row_info, png_bytep data)
2830 See pngtest.c for a working example. Your function will be called
2831 after all of the other transformations have been processed. Take care with
2832 interlaced images if you do the interlace yourself - the width of the row is the
2833 width in 'row_info', not the overall image width.
2835 If supported, libpng provides two information routines that you can use to find
2836 where you are in processing the image:
2838 png_get_current_pass_number(png_structp png_ptr);
2839 png_get_current_row_number(png_structp png_ptr);
2841 Don't try using these outside a transform callback - firstly they are only
2842 supported if user transforms are supported, secondly they may well return
2843 unexpected results unless the row is actually being processed at the moment they
2847 images the value returned is the row in the input sub-image image. Use
2848 PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
2849 find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
2851 The discussion of interlace handling above contains more information on how to
2854 You can also set up a pointer to a user structure for use by your
2855 callback function, and you can inform libpng that your transform
2856 function will change the number of channels or bit depth with the
2859 png_set_user_transform_info(png_ptr, user_ptr,
2860 user_depth, user_channels);
2862 The user's application, not libpng, is responsible for allocating and
2863 freeing any memory required for the user structure.
2865 You can retrieve the pointer via the function
2866 png_get_user_transform_ptr(). For example:
2868 voidp read_user_transform_ptr =
2869 png_get_user_transform_ptr(png_ptr);
2871 The last thing to handle is interlacing; this is covered in detail below,
2872 but you must call the function here if you want libpng to handle expansion
2873 of the interlaced image.
2875 number_of_passes = png_set_interlace_handling(png_ptr);
2877 After setting the transformations, libpng can update your png_info
2878 structure to reflect any transformations you've requested with this
2881 png_read_update_info(png_ptr, info_ptr);
2883 This is most useful to update the info structure's rowbytes
2884 field so you can use it to allocate your image memory. This function
2885 will also update your palette with the correct screen_gamma and
2886 background if these have been given with the calls above. You may
2887 only call png_read_update_info() once with a particular info_ptr.
2889 After you call png_read_update_info(), you can allocate any
2890 memory you need to hold the image. The row data is simply
2891 raw byte data for all forms of images. As the actual allocation
2892 varies among applications, no example will be given. If you
2893 are allocating one large chunk, you will need to build an
2894 array of pointers to each row, as it will be needed for some
2895 of the functions below.
2897 Remember: Before you call png_read_update_info(), the png_get_*()
2898 functions return the values corresponding to the original PNG image.
2899 After you call png_read_update_info the values refer to the image
2900 that libpng will output. Consequently you must call all the png_set_
2901 functions before you call png_read_update_info(). This is particularly
2902 important for png_set_interlace_handling() - if you are going to call
2903 png_read_update_info() you must call png_set_interlace_handling() before
2904 it unless you want to receive interlaced output.
2906 .SS Reading image data
2908 After you've allocated memory, you can read the image data.
2909 The simplest way to do this is in one function call. If you are
2910 allocating enough memory to hold the whole image, you can just
2911 call png_read_image() and libpng will read in all the image data
2912 and put it in the memory area supplied. You will need to pass in
2913 an array of pointers to each row.
2915 This function automatically handles interlacing, so you don't
2916 need to call png_set_interlace_handling() (unless you call
2917 png_read_update_info()) or call this function multiple times, or any
2918 of that other stuff necessary with png_read_rows().
2920 png_read_image(png_ptr, row_pointers);
2922 where row_pointers is:
2924 png_bytep row_pointers[height];
2926 You can point to void or char or whatever you use for pixels.
2928 If you don't want to read in the whole image at once, you can
2929 use png_read_rows() instead. If there is no interlacing (check
2930 interlace_type == PNG_INTERLACE_NONE), this is simple:
2932 png_read_rows(png_ptr, row_pointers, NULL,
2935 where row_pointers is the same as in the png_read_image() call.
2937 If you are doing this just one row at a time, you can do this with
2938 a single row_pointer instead of an array of row_pointers:
2940 png_bytep row_pointer = row;
2941 png_read_row(png_ptr, row_pointer, NULL);
2943 If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
2944 get somewhat harder. The only current (PNG Specification version 1.2)
2945 interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7);
2946 a somewhat complicated 2D interlace scheme, known as Adam7, that
2947 breaks down an image into seven smaller images of varying size, based
2948 on an 8x8 grid. This number is defined (from libpng 1.5) as
2949 PNG_INTERLACE_ADAM7_PASSES in png.h
2951 libpng can fill out those images or it can give them to you "as is".
2952 It is almost always better to have libpng handle the interlacing for you.
2953 If you want the images filled out, there are two ways to do that. The one
2954 mentioned in the PNG specification is to expand each pixel to cover
2955 those pixels that have not been read yet (the "rectangle" method).
2956 This results in a blocky image for the first pass, which gradually
2957 smooths out as more pixels are read. The other method is the "sparkle"
2958 method, where pixels are drawn only in their final locations, with the
2959 rest of the image remaining whatever colors they were initialized to
2960 before the start of the read. The first method usually looks better,
2961 but tends to be slower, as there are more pixels to put in the rows.
2963 If, as is likely, you want libpng to expand the images, call this before
2964 calling png_start_read_image() or png_read_update_info():
2966 if (interlace_type == PNG_INTERLACE_ADAM7)
2968 = png_set_interlace_handling(png_ptr);
2970 This will return the number of passes needed. Currently, this is seven,
2971 but may change if another interlace type is added. This function can be
2972 called even if the file is not interlaced, where it will return one pass.
2973 You then need to read the whole image 'number_of_passes' times. Each time
2974 will distribute the pixels from the current pass to the correct place in
2975 the output image, so you need to supply the same rows to png_read_rows in
2978 If you are not going to display the image after each pass, but are
2979 going to wait until the entire image is read in, use the sparkle
2980 effect. This effect is faster and the end result of either method
2981 is exactly the same. If you are planning on displaying the image
2982 after each pass, the "rectangle" effect is generally considered the
2985 If you only want the "sparkle" effect, just call png_read_rows() as
2986 normal, with the third parameter NULL. Make sure you make pass over
2987 the image number_of_passes times, and you don't change the data in the
2988 rows between calls. You can change the locations of the data, just
2989 not the data. Each pass only writes the pixels appropriate for that
2990 pass, and assumes the data from previous passes is still valid.
2992 png_read_rows(png_ptr, row_pointers, NULL,
2995 If you only want the first effect (the rectangles), do the same as
2996 before except pass the row buffer in the third parameter, and leave
2997 the second parameter NULL.
2999 png_read_rows(png_ptr, NULL, row_pointers,
3002 If you don't want libpng to handle the interlacing details, just call
3003 png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.
3004 Each of the images is a valid image by itself, however you will almost
3005 certainly need to distribute the pixels from each sub-image to the
3006 correct place. This is where everything gets very tricky.
3008 If you want to retrieve the separate images you must pass the correct
3009 number of rows to each successive call of png_read_rows(). The calculation
3010 gets pretty complicated for small images, where some sub-images may
3011 not even exist because either their width or height ends up zero.
3012 libpng provides two macros to help you in 1.5 and later versions:
3014 png_uint_32 width = PNG_PASS_COLS(image_width, pass_number);
3015 png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number);
3017 Respectively these tell you the width and height of the sub-image
3018 corresponding to the numbered pass. 'pass' is in in the range 0 to 6 -
3019 this can be confusing because the specification refers to the same passes
3020 as 1 to 7! Be careful, you must check both the width and height before
3021 calling png_read_rows() and not call it for that pass if either is zero.
3023 You can, of course, read each sub-image row by row. If you want to
3024 produce optimal code to make a pixel-by-pixel transformation of an
3025 interlaced image this is the best approach; read each row of each pass,
3026 transform it, and write it out to a new interlaced image.
3028 If you want to de-interlace the image yourself libpng provides further
3029 macros to help that tell you where to place the pixels in the output image.
3030 Because the interlacing scheme is rectangular - sub-image pixels are always
3031 arranged on a rectangular grid - all you need to know for each pass is the
3032 starting column and row in the output image of the first pixel plus the
3033 spacing between each pixel. As of libpng 1.5 there are four macros to
3034 retrieve this information:
3036 png_uint_32 x = PNG_PASS_START_COL(pass);
3037 png_uint_32 y = PNG_PASS_START_ROW(pass);
3038 png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass);
3039 png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass);
3041 These allow you to write the obvious loop:
3043 png_uint_32 input_y = 0;
3044 png_uint_32 output_y = PNG_PASS_START_ROW(pass);
3046 while (output_y < output_image_height)
3048 png_uint_32 input_x = 0;
3049 png_uint_32 output_x = PNG_PASS_START_COL(pass);
3051 while (output_x < output_image_width)
3053 image[output_y][output_x] =
3054 subimage[pass][input_y][input_x++];
3063 Notice that the steps between successive output rows and columns are
3064 returned as shifts. This is possible because the pixels in the subimages
3065 are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original
3066 image. In practice you may need to directly calculate the output coordinate
3067 given an input coordinate. libpng provides two further macros for this
3070 png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass);
3071 png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass);
3073 Finally a pair of macros are provided to tell you if a particular image
3074 row or column appears in a given pass:
3076 int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass);
3077 int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass);
3079 Bear in mind that you will probably also need to check the width and height
3080 of the pass in addition to the above to be sure the pass even exists!
3082 With any luck you are convinced by now that you don't want to do your own
3083 interlace handling. In reality normally the only good reason for doing this
3084 is if you are processing PNG files on a pixel-by-pixel basis and don't want
3085 to load the whole file into memory when it is interlaced.
3087 libpng includes a test program, pngvalid, that illustrates reading and
3088 writing of interlaced images. If you can't get interlacing to work in your
3089 code and don't want to leave it to libpng (the recommended approach), see
3090 how pngvalid.c does it.
3092 .SS Finishing a sequential read
3094 After you are finished reading the image through the
3095 low-level interface, you can finish reading the file. If you are
3096 interested in comments or time, which may be stored either before or
3097 after the image data, you should pass the separate png_info struct if
3098 you want to keep the comments from before and after the image
3101 png_infop end_info = png_create_info_struct(png_ptr);
3105 png_destroy_read_struct(&png_ptr, &info_ptr,
3110 png_read_end(png_ptr, end_info);
3112 If you are not interested, you should still call png_read_end()
3113 but you can pass NULL, avoiding the need to create an end_info structure.
3115 png_read_end(png_ptr, (png_infop)NULL);
3117 If you don't call png_read_end(), then your file pointer will be
3118 left pointing to the first chunk after the last IDAT, which is probably
3119 not what you want if you expect to read something beyond the end of
3122 When you are done, you can free all memory allocated by libpng like this:
3124 png_destroy_read_struct(&png_ptr, &info_ptr,
3127 or, if you didn't create an end_info structure,
3129 png_destroy_read_struct(&png_ptr, &info_ptr,
3132 It is also possible to individually free the info_ptr members that
3133 point to libpng-allocated storage with the following function:
3135 png_free_data(png_ptr, info_ptr, mask, seq)
3137 mask - identifies data to be freed, a mask
3138 containing the bitwise OR of one or
3140 PNG_FREE_PLTE, PNG_FREE_TRNS,
3141 PNG_FREE_HIST, PNG_FREE_ICCP,
3142 PNG_FREE_PCAL, PNG_FREE_ROWS,
3143 PNG_FREE_SCAL, PNG_FREE_SPLT,
3144 PNG_FREE_TEXT, PNG_FREE_UNKN,
3145 or simply PNG_FREE_ALL
3147 seq - sequence number of item to be freed
3150 This function may be safely called when the relevant storage has
3151 already been freed, or has not yet been allocated, or was allocated
3152 by the user and not by libpng, and will in those cases do nothing.
3153 The "seq" parameter is ignored if only one item of the selected data
3154 type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
3155 are allowed for the data type identified in the mask, such as text or
3156 sPLT, only the n'th item in the structure is freed, where n is "seq".
3158 The default behavior is only to free data that was allocated internally
3159 by libpng. This can be changed, so that libpng will not free the data,
3160 or so that it will free data that was allocated by the user with png_malloc()
3161 or png_zalloc() and passed in via a png_set_*() function, with
3163 png_data_freer(png_ptr, info_ptr, freer, mask)
3166 PNG_DESTROY_WILL_FREE_DATA
3167 PNG_SET_WILL_FREE_DATA
3168 PNG_USER_WILL_FREE_DATA
3170 mask - which data elements are affected
3171 same choices as in png_free_data()
3173 This function only affects data that has already been allocated.
3174 You can call this function after reading the PNG data but before calling
3175 any png_set_*() functions, to control whether the user or the png_set_*()
3176 function is responsible for freeing any existing data that might be present,
3177 and again after the png_set_*() functions to control whether the user
3178 or png_destroy_*() is supposed to free the data. When the user assumes
3179 responsibility for libpng-allocated data, the application must use
3180 png_free() to free it, and when the user transfers responsibility to libpng
3181 for data that the user has allocated, the user must have used png_malloc()
3182 or png_zalloc() to allocate it.
3184 If you allocated your row_pointers in a single block, as suggested above in
3185 the description of the high level read interface, you must not transfer
3186 responsibility for freeing it to the png_set_rows or png_read_destroy function,
3187 because they would also try to free the individual row_pointers[i].
3189 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3190 separately, do not transfer responsibility for freeing text_ptr to libpng,
3191 because when libpng fills a png_text structure it combines these members with
3192 the key member, and png_free_data() will free only text_ptr.key. Similarly,
3193 if you transfer responsibility for free'ing text_ptr from libpng to your
3194 application, your application must not separately free those members.
3196 The png_free_data() function will turn off the "valid" flag for anything
3197 it frees. If you need to turn the flag off for a chunk that was freed by
3198 your application instead of by libpng, you can use
3200 png_set_invalid(png_ptr, info_ptr, mask);
3202 mask - identifies the chunks to be made invalid,
3203 containing the bitwise OR of one or
3205 PNG_INFO_gAMA, PNG_INFO_sBIT,
3206 PNG_INFO_cHRM, PNG_INFO_PLTE,
3207 PNG_INFO_tRNS, PNG_INFO_bKGD,
3208 PNG_INFO_hIST, PNG_INFO_pHYs,
3209 PNG_INFO_oFFs, PNG_INFO_tIME,
3210 PNG_INFO_pCAL, PNG_INFO_sRGB,
3211 PNG_INFO_iCCP, PNG_INFO_sPLT,
3212 PNG_INFO_sCAL, PNG_INFO_IDAT
3214 For a more compact example of reading a PNG image, see the file example.c.
3216 .SS Reading PNG files progressively
3218 The progressive reader is slightly different then the non-progressive
3219 reader. Instead of calling png_read_info(), png_read_rows(), and
3220 png_read_end(), you make one call to png_process_data(), which calls
3221 callbacks when it has the info, a row, or the end of the image. You
3222 set up these callbacks with png_set_progressive_read_fn(). You don't
3223 have to worry about the input/output functions of libpng, as you are
3224 giving the library the data directly in png_process_data(). I will
3225 assume that you have read the section on reading PNG files above,
3226 so I will only highlight the differences (although I will show
3229 png_structp png_ptr;
3232 /* An example code fragment of how you would
3233 initialize the progressive reader in your
3236 initialize_png_reader()
3238 png_ptr = png_create_read_struct
3239 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3240 user_error_fn, user_warning_fn);
3245 info_ptr = png_create_info_struct(png_ptr);
3249 png_destroy_read_struct(&png_ptr,
3250 (png_infopp)NULL, (png_infopp)NULL);
3254 if (setjmp(png_jmpbuf(png_ptr)))
3256 png_destroy_read_struct(&png_ptr, &info_ptr,
3261 /* This one's new. You can provide functions
3262 to be called when the header info is valid,
3263 when each row is completed, and when the image
3264 is finished. If you aren't using all functions,
3265 you can specify NULL parameters. Even when all
3266 three functions are NULL, you need to call
3267 png_set_progressive_read_fn(). You can use
3268 any struct as the user_ptr (cast to a void pointer
3269 for the function call), and retrieve the pointer
3270 from inside the callbacks using the function
3272 png_get_progressive_ptr(png_ptr);
3274 which will return a void pointer, which you have
3275 to cast appropriately.
3277 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
3278 info_callback, row_callback, end_callback);
3283 /* A code fragment that you call as you receive blocks
3286 process_data(png_bytep buffer, png_uint_32 length)
3288 if (setjmp(png_jmpbuf(png_ptr)))
3290 png_destroy_read_struct(&png_ptr, &info_ptr,
3295 /* This one's new also. Simply give it a chunk
3296 of data from the file stream (in order, of
3297 course). On machines with segmented memory
3298 models machines, don't give it any more than
3299 64K. The library seems to run fine with sizes
3300 of 4K. Although you can give it much less if
3301 necessary (I assume you can give it chunks of
3302 1 byte, I haven't tried less then 256 bytes
3303 yet). When this function returns, you may
3304 want to display any rows that were generated
3305 in the row callback if you don't already do
3308 png_process_data(png_ptr, info_ptr, buffer, length);
3310 /* At this point you can call png_process_data_skip if
3311 you want to handle data the library will skip yourself;
3312 it simply returns the number of bytes to skip (and stops
3313 libpng skipping that number of bytes on the next
3314 png_process_data call).
3318 /* This function is called (as set by
3319 png_set_progressive_read_fn() above) when enough data
3320 has been supplied so all of the header has been
3324 info_callback(png_structp png_ptr, png_infop info)
3326 /* Do any setup here, including setting any of
3327 the transformations mentioned in the Reading
3328 PNG files section. For now, you _must_ call
3329 either png_start_read_image() or
3330 png_read_update_info() after all the
3331 transformations are set (even if you don't set
3332 any). You may start getting rows before
3333 png_process_data() returns, so this is your
3334 last chance to prepare for that.
3336 This is where you turn on interlace handling,
3337 assuming you don't want to do it yourself.
3339 If you need to you can stop the processing of
3340 your original input data at this point by calling
3341 png_process_data_pause. This returns the number
3342 of unprocessed bytes from the last png_process_data
3343 call - it is up to you to ensure that the next call
3344 sees these bytes again. If you don't want to bother
3345 with this you can get libpng to cache the unread
3346 bytes by setting the 'save' parameter (see png.h) but
3347 then libpng will have to copy the data internally.
3351 /* This function is called when each row of image
3354 row_callback(png_structp png_ptr, png_bytep new_row,
3355 png_uint_32 row_num, int pass)
3357 /* If the image is interlaced, and you turned
3358 on the interlace handler, this function will
3359 be called for every row in every pass. Some
3360 of these rows will not be changed from the
3361 previous pass. When the row is not changed,
3362 the new_row variable will be NULL. The rows
3363 and passes are called in order, so you don't
3364 really need the row_num and pass, but I'm
3365 supplying them because it may make your life
3368 If you did not turn on interlace handling then
3369 the callback is called for each row of each
3370 sub-image when the image is interlaced. In this
3371 case 'row_num' is the row in the sub-image, not
3372 the row in the output image as it is in all other
3375 For the non-NULL rows of interlaced images when
3376 you have switched on libpng interlace handling,
3377 you must call png_progressive_combine_row()
3378 passing in the row and the old row. You can
3379 call this function for NULL rows (it will just
3380 return) and for non-interlaced images (it just
3381 does the memcpy for you) if it will make the
3382 code easier. Thus, you can just do this for
3383 all cases if you switch on interlace handling;
3386 png_progressive_combine_row(png_ptr, old_row,
3389 /* where old_row is what was displayed for
3390 previously for the row. Note that the first
3391 pass (pass == 0, really) will completely cover
3392 the old row, so the rows do not have to be
3393 initialized. After the first pass (and only
3394 for interlaced images), you will have to pass
3395 the current row, and the function will combine
3396 the old row and the new row.
3398 You can also call png_process_data_pause in this
3399 callback - see above.
3404 end_callback(png_structp png_ptr, png_infop info)
3406 /* This function is called after the whole image
3407 has been read, including any chunks after the
3408 image (up to and including the IEND). You
3409 will usually have the same info chunk as you
3410 had in the header, although some data may have
3411 been added to the comments and time fields.
3413 Most people won't do much here, perhaps setting
3414 a flag that marks the image as finished.
3422 Much of this is very similar to reading. However, everything of
3423 importance is repeated here, so you won't have to constantly look
3424 back up in the reading section to understand writing.
3428 You will want to do the I/O initialization before you get into libpng,
3429 so if it doesn't work, you don't have anything to undo. If you are not
3430 using the standard I/O functions, you will need to replace them with
3431 custom writing functions. See the discussion under Customizing libpng.
3433 FILE *fp = fopen(file_name, "wb");
3438 Next, png_struct and png_info need to be allocated and initialized.
3439 As these can be both relatively large, you may not want to store these
3440 on the stack, unless you have stack space to spare. Of course, you
3441 will want to check if they return NULL. If you are also reading,
3442 you won't want to name your read structure and your write structure
3443 both "png_ptr"; you can call them anything you like, such as
3444 "read_ptr" and "write_ptr". Look at pngtest.c, for example.
3446 png_structp png_ptr = png_create_write_struct
3447 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3448 user_error_fn, user_warning_fn);
3453 png_infop info_ptr = png_create_info_struct(png_ptr);
3456 png_destroy_write_struct(&png_ptr,
3461 If you want to use your own memory allocation routines,
3462 define PNG_USER_MEM_SUPPORTED and use
3463 png_create_write_struct_2() instead of png_create_write_struct():
3465 png_structp png_ptr = png_create_write_struct_2
3466 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3467 user_error_fn, user_warning_fn, (png_voidp)
3468 user_mem_ptr, user_malloc_fn, user_free_fn);
3470 After you have these structures, you will need to set up the
3471 error handling. When libpng encounters an error, it expects to
3472 longjmp() back to your routine. Therefore, you will need to call
3473 setjmp() and pass the png_jmpbuf(png_ptr). If you
3474 write the file from different routines, you will need to update
3475 the png_jmpbuf(png_ptr) every time you enter a new routine that will
3476 call a png_*() function. See your documentation of setjmp/longjmp
3477 for your compiler for more information on setjmp/longjmp. See
3478 the discussion on libpng error handling in the Customizing Libpng
3479 section below for more information on the libpng error handling.
3481 if (setjmp(png_jmpbuf(png_ptr)))
3483 png_destroy_write_struct(&png_ptr, &info_ptr);
3490 If you would rather avoid the complexity of setjmp/longjmp issues,
3491 you can compile libpng with PNG_NO_SETJMP, in which case
3492 errors will result in a call to PNG_ABORT() which defaults to abort().
3494 You can #define PNG_ABORT() to a function that does something
3495 more useful than abort(), as long as your function does not
3498 Now you need to set up the output code. The default for libpng is to
3499 use the C function fwrite(). If you use this, you will need to pass a
3500 valid FILE * in the function png_init_io(). Be sure that the file is
3501 opened in binary mode. Again, if you wish to handle writing data in
3502 another way, see the discussion on libpng I/O handling in the Customizing
3503 Libpng section below.
3505 png_init_io(png_ptr, fp);
3507 If you are embedding your PNG into a datastream such as MNG, and don't
3508 want libpng to write the 8-byte signature, or if you have already
3509 written the signature in your application, use
3511 png_set_sig_bytes(png_ptr, 8);
3513 to inform libpng that it should not write a signature.
3517 At this point, you can set up a callback function that will be
3518 called after each row has been written, which you can use to control
3519 a progress meter or the like. It's demonstrated in pngtest.c.
3520 You must supply a function
3522 void write_row_callback(png_structp png_ptr, png_uint_32 row,
3525 /* put your code here */
3528 (You can give it another name that you like instead of "write_row_callback")
3530 To inform libpng about your function, use
3532 png_set_write_status_fn(png_ptr, write_row_callback);
3534 When this function is called the row has already been completely processed and
3535 it has also been written out. The 'row' and 'pass' refer to the next row to be
3537 non-interlaced case the row that was just handled is simply one less than the
3538 passed in row number, and pass will always be 0. For the interlaced case the
3539 same applies unless the row value is 0, in which case the row just handled was
3540 the last one from one of the preceding passes. Because interlacing may skip a
3541 pass you cannot be sure that the preceding pass is just 'pass-1', if you really
3542 need to know what the last pass is record (row,pass) from the callback and use
3543 the last recorded value each time.
3545 As with the user transform you can find the output row using the
3546 PNG_ROW_FROM_PASS_ROW macro.
3548 You now have the option of modifying how the compression library will
3549 run. The following functions are mainly for testing, but may be useful
3550 in some cases, like if you need to write PNG files extremely fast and
3551 are willing to give up some compression, or if you want to get the
3552 maximum possible compression at the expense of slower writing. If you
3553 have no special needs in this area, let the library do what it wants by
3554 not calling this function at all, as it has been tuned to deliver a good
3555 speed/compression ratio. The second parameter to png_set_filter() is
3556 the filter method, for which the only valid values are 0 (as of the
3557 July 1999 PNG specification, version 1.2) or 64 (if you are writing
3558 a PNG datastream that is to be embedded in a MNG datastream). The third
3559 parameter is a flag that indicates which filter type(s) are to be tested
3560 for each scanline. See the PNG specification for details on the specific
3564 /* turn on or off filtering, and/or choose
3565 specific filters. You can use either a single
3566 PNG_FILTER_VALUE_NAME or the bitwise OR of one
3567 or more PNG_FILTER_NAME masks.
3569 png_set_filter(png_ptr, 0,
3570 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
3571 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
3572 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
3573 PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
3574 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
3577 If an application wants to start and stop using particular filters during
3578 compression, it should start out with all of the filters (to ensure that
3579 the previous row of pixels will be stored in case it's needed later),
3580 and then add and remove them after the start of compression.
3582 If you are writing a PNG datastream that is to be embedded in a MNG
3583 datastream, the second parameter can be either 0 or 64.
3585 The png_set_compression_*() functions interface to the zlib compression
3586 library, and should mostly be ignored unless you really know what you are
3587 doing. The only generally useful call is png_set_compression_level()
3588 which changes how much time zlib spends on trying to compress the image
3589 data. See the Compression Library (zlib.h and algorithm.txt, distributed
3590 with zlib) for details on the compression levels.
3594 /* Set the zlib compression level */
3595 png_set_compression_level(png_ptr,
3596 Z_BEST_COMPRESSION);
3598 /* Set other zlib parameters for compressing IDAT */
3599 png_set_compression_mem_level(png_ptr, 8);
3600 png_set_compression_strategy(png_ptr,
3601 Z_DEFAULT_STRATEGY);
3602 png_set_compression_window_bits(png_ptr, 15);
3603 png_set_compression_method(png_ptr, 8);
3604 png_set_compression_buffer_size(png_ptr, 8192)
3606 /* Set zlib parameters for text compression
3607 * If you don't call these, the parameters
3608 * fall back on those defined for IDAT chunks
3610 png_set_text_compression_mem_level(png_ptr, 8);
3611 png_set_text_compression_strategy(png_ptr,
3612 Z_DEFAULT_STRATEGY);
3613 png_set_text_compression_window_bits(png_ptr, 15);
3614 png_set_text_compression_method(png_ptr, 8);
3616 .SS Setting the contents of info for output
3618 You now need to fill in the png_info structure with all the data you
3619 wish to write before the actual image. Note that the only thing you
3620 are allowed to write after the image is the text chunks and the time
3621 chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
3622 the latest PNG specification for more information on that. If you
3623 wish to write them before the image, fill them in now, and flag that
3624 data as being valid. If you want to wait until after the data, don't
3625 fill them until png_write_end(). For all the fields in png_info and
3626 their data types, see png.h. For explanations of what the fields
3627 contain, see the PNG specification.
3629 Some of the more important parts of the png_info are:
3631 png_set_IHDR(png_ptr, info_ptr, width, height,
3632 bit_depth, color_type, interlace_type,
3633 compression_type, filter_method)
3635 width - holds the width of the image
3636 in pixels (up to 2^31).
3638 height - holds the height of the image
3639 in pixels (up to 2^31).
3641 bit_depth - holds the bit depth of one of the
3643 (valid values are 1, 2, 4, 8, 16
3644 and depend also on the
3645 color_type. See also significant
3648 color_type - describes which color/alpha
3649 channels are present.
3651 (bit depths 1, 2, 4, 8, 16)
3652 PNG_COLOR_TYPE_GRAY_ALPHA
3654 PNG_COLOR_TYPE_PALETTE
3655 (bit depths 1, 2, 4, 8)
3658 PNG_COLOR_TYPE_RGB_ALPHA
3661 PNG_COLOR_MASK_PALETTE
3662 PNG_COLOR_MASK_COLOR
3663 PNG_COLOR_MASK_ALPHA
3665 interlace_type - PNG_INTERLACE_NONE or
3668 compression_type - (must be
3669 PNG_COMPRESSION_TYPE_DEFAULT)
3671 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
3672 or, if you are writing a PNG to
3673 be embedded in a MNG datastream,
3675 PNG_INTRAPIXEL_DIFFERENCING)
3677 If you call png_set_IHDR(), the call must appear before any of the
3678 other png_set_*() functions, because they might require access to some of
3679 the IHDR settings. The remaining png_set_*() functions can be called
3682 If you wish, you can reset the compression_type, interlace_type, or
3683 filter_method later by calling png_set_IHDR() again; if you do this, the
3684 width, height, bit_depth, and color_type must be the same in each call.
3686 png_set_PLTE(png_ptr, info_ptr, palette,
3689 palette - the palette for the file
3690 (array of png_color)
3691 num_palette - number of entries in the palette
3693 png_set_gAMA(png_ptr, info_ptr, file_gamma);
3694 png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma);
3696 file_gamma - the gamma at which the image was
3697 created (PNG_INFO_gAMA)
3699 int_file_gamma - 100,000 times the gamma at which
3700 the image was created
3702 png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y,
3703 green_x, green_y, blue_x, blue_y)
3704 png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X,
3705 green_Y, green_Z, blue_X, blue_Y, blue_Z)
3706 png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y,
3707 int_red_x, int_red_y, int_green_x, int_green_y,
3708 int_blue_x, int_blue_y)
3709 png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y,
3710 int_red_Z, int_green_X, int_green_Y, int_green_Z,
3711 int_blue_X, int_blue_Y, int_blue_Z)
3713 {white,red,green,blue}_{x,y}
3714 A color space encoding specified using the chromaticities
3715 of the end points and the white point.
3717 {red,green,blue}_{X,Y,Z}
3718 A color space encoding specified using the encoding end
3719 points - the CIE tristimulus specification of the intended
3720 color of the red, green and blue channels in the PNG RGB
3721 data. The white point is simply the sum of the three end
3724 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
3726 srgb_intent - the rendering intent
3727 (PNG_INFO_sRGB) The presence of
3728 the sRGB chunk means that the pixel
3729 data is in the sRGB color space.
3730 This chunk also implies specific
3731 values of gAMA and cHRM. Rendering
3732 intent is the CSS-1 property that
3733 has been defined by the International
3735 (http://www.color.org).
3737 PNG_sRGB_INTENT_SATURATION,
3738 PNG_sRGB_INTENT_PERCEPTUAL,
3739 PNG_sRGB_INTENT_ABSOLUTE, or
3740 PNG_sRGB_INTENT_RELATIVE.
3743 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
3746 srgb_intent - the rendering intent
3747 (PNG_INFO_sRGB) The presence of the
3748 sRGB chunk means that the pixel
3749 data is in the sRGB color space.
3750 This function also causes gAMA and
3751 cHRM chunks with the specific values
3752 that are consistent with sRGB to be
3755 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
3758 name - The profile name.
3760 compression_type - The compression type; always
3761 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
3762 You may give NULL to this argument to
3765 profile - International Color Consortium color
3766 profile data. May contain NULs.
3768 proflen - length of profile data in bytes.
3770 png_set_sBIT(png_ptr, info_ptr, sig_bit);
3772 sig_bit - the number of significant bits for
3773 (PNG_INFO_sBIT) each of the gray, red,
3774 green, and blue channels, whichever are
3775 appropriate for the given color type
3778 png_set_tRNS(png_ptr, info_ptr, trans_alpha,
3779 num_trans, trans_color);
3781 trans_alpha - array of alpha (transparency)
3782 entries for palette (PNG_INFO_tRNS)
3784 num_trans - number of transparent entries
3787 trans_color - graylevel or color sample values
3788 (in order red, green, blue) of the
3789 single transparent color for
3790 non-paletted images (PNG_INFO_tRNS)
3792 png_set_hIST(png_ptr, info_ptr, hist);
3794 hist - histogram of palette (array of
3795 png_uint_16) (PNG_INFO_hIST)
3797 png_set_tIME(png_ptr, info_ptr, mod_time);
3799 mod_time - time image was last modified
3802 png_set_bKGD(png_ptr, info_ptr, background);
3804 background - background color (of type
3805 png_color_16p) (PNG_VALID_bKGD)
3807 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
3809 text_ptr - array of png_text holding image
3812 text_ptr[i].compression - type of compression used
3813 on "text" PNG_TEXT_COMPRESSION_NONE
3814 PNG_TEXT_COMPRESSION_zTXt
3815 PNG_ITXT_COMPRESSION_NONE
3816 PNG_ITXT_COMPRESSION_zTXt
3817 text_ptr[i].key - keyword for comment. Must contain
3819 text_ptr[i].text - text comments for current
3820 keyword. Can be NULL or empty.
3821 text_ptr[i].text_length - length of text string,
3822 after decompression, 0 for iTXt
3823 text_ptr[i].itxt_length - length of itxt string,
3824 after decompression, 0 for tEXt/zTXt
3825 text_ptr[i].lang - language of comment (NULL or
3827 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
3828 or empty for unknown).
3829 Note that the itxt_length, lang, and lang_key
3830 members of the text_ptr structure only exist
3831 when the library is built with iTXt chunk support.
3832 Prior to libpng-1.4.0 the library was built by default
3833 without iTXt support.
3835 num_text - number of comments
3837 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
3840 palette_ptr - array of png_sPLT_struct structures
3841 to be added to the list of palettes
3842 in the info structure.
3843 num_spalettes - number of palette structures to be
3846 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
3849 offset_x - positive offset from the left
3852 offset_y - positive offset from the top
3855 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
3857 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
3860 res_x - pixels/unit physical resolution
3863 res_y - pixels/unit physical resolution
3866 unit_type - PNG_RESOLUTION_UNKNOWN,
3867 PNG_RESOLUTION_METER
3869 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
3871 unit - physical scale units (an integer)
3873 width - width of a pixel in physical scale units
3875 height - height of a pixel in physical scale units
3876 (width and height are doubles)
3878 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
3880 unit - physical scale units (an integer)
3882 width - width of a pixel in physical scale units
3883 expressed as a string
3885 height - height of a pixel in physical scale units
3886 (width and height are strings like "2.54")
3888 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
3891 unknowns - array of png_unknown_chunk
3892 structures holding unknown chunks
3893 unknowns[i].name - name of unknown chunk
3894 unknowns[i].data - data of unknown chunk
3895 unknowns[i].size - size of unknown chunk's data
3896 unknowns[i].location - position to write chunk in file
3897 0: do not write chunk
3898 PNG_HAVE_IHDR: before PLTE
3899 PNG_HAVE_PLTE: before IDAT
3900 PNG_AFTER_IDAT: after IDAT
3902 The "location" member is set automatically according to
3903 what part of the output file has already been written.
3904 You can change its value after calling png_set_unknown_chunks()
3905 as demonstrated in pngtest.c. Within each of the "locations",
3906 the chunks are sequenced according to their position in the
3907 structure (that is, the value of "i", which is the order in which
3908 the chunk was either read from the input file or defined with
3909 png_set_unknown_chunks).
3911 A quick word about text and num_text. text is an array of png_text
3912 structures. num_text is the number of valid structures in the array.
3913 Each png_text structure holds a language code, a keyword, a text value,
3914 and a compression type.
3916 The compression types have the same valid numbers as the compression
3917 types of the image data. Currently, the only valid number is zero.
3918 However, you can store text either compressed or uncompressed, unlike
3919 images, which always have to be compressed. So if you don't want the
3920 text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
3921 Because tEXt and zTXt chunks don't have a language field, if you
3922 specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
3923 any language code or translated keyword will not be written out.
3925 Until text gets around a few hundred bytes, it is not worth compressing it.
3926 After the text has been written out to the file, the compression type
3927 is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
3928 so that it isn't written out again at the end (in case you are calling
3929 png_write_end() with the same struct).
3931 The keywords that are given in the PNG Specification are:
3933 Title Short (one line) title or
3936 Author Name of image's creator
3938 Description Description of image (possibly long)
3940 Copyright Copyright notice
3942 Creation Time Time of original image creation
3943 (usually RFC 1123 format, see below)
3945 Software Software used to create the image
3947 Disclaimer Legal disclaimer
3949 Warning Warning of nature of content
3951 Source Device used to create the image
3953 Comment Miscellaneous comment; conversion
3954 from other image format
3956 The keyword-text pairs work like this. Keywords should be short
3957 simple descriptions of what the comment is about. Some typical
3958 keywords are found in the PNG specification, as is some recommendations
3959 on keywords. You can repeat keywords in a file. You can even write
3960 some text before the image and some after. For example, you may want
3961 to put a description of the image before the image, but leave the
3962 disclaimer until after, so viewers working over modem connections
3963 don't have to wait for the disclaimer to go over the modem before
3964 they start seeing the image. Finally, keywords should be full
3965 words, not abbreviations. Keywords and text are in the ISO 8859-1
3966 (Latin-1) character set (a superset of regular ASCII) and can not
3967 contain NUL characters, and should not contain control or other
3968 unprintable characters. To make the comments widely readable, stick
3969 with basic ASCII, and avoid machine specific character set extensions
3970 like the IBM-PC character set. The keyword must be present, but
3971 you can leave off the text string on non-compressed pairs.
3972 Compressed pairs must have a text string, as only the text string
3973 is compressed anyway, so the compression would be meaningless.
3975 PNG supports modification time via the png_time structure. Two
3976 conversion routines are provided, png_convert_from_time_t() for
3977 time_t and png_convert_from_struct_tm() for struct tm. The
3978 time_t routine uses gmtime(). You don't have to use either of
3979 these, but if you wish to fill in the png_time structure directly,
3980 you should provide the time in universal time (GMT) if possible
3981 instead of your local time. Note that the year number is the full
3982 year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
3983 that months start with 1.
3985 If you want to store the time of the original image creation, you should
3986 use a plain tEXt chunk with the "Creation Time" keyword. This is
3987 necessary because the "creation time" of a PNG image is somewhat vague,
3988 depending on whether you mean the PNG file, the time the image was
3989 created in a non-PNG format, a still photo from which the image was
3990 scanned, or possibly the subject matter itself. In order to facilitate
3991 machine-readable dates, it is recommended that the "Creation Time"
3992 tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
3993 although this isn't a requirement. Unlike the tIME chunk, the
3994 "Creation Time" tEXt chunk is not expected to be automatically changed
3995 by the software. To facilitate the use of RFC 1123 dates, a function
3996 png_convert_to_rfc1123(png_timep) is provided to convert from PNG
3997 time to an RFC 1123 format string.
3999 .SS Writing unknown chunks
4001 You can use the png_set_unknown_chunks function to queue up chunks
4002 for writing. You give it a chunk name, raw data, and a size; that's
4003 all there is to it. The chunks will be written by the next following
4004 png_write_info_before_PLTE, png_write_info, or png_write_end function.
4005 Any chunks previously read into the info structure's unknown-chunk
4006 list will also be written out in a sequence that satisfies the PNG
4007 specification's ordering rules.
4009 .SS The high-level write interface
4011 At this point there are two ways to proceed; through the high-level
4012 write interface, or through a sequence of low-level write operations.
4013 You can use the high-level interface if your image data is present
4014 in the info structure. All defined output
4015 transformations are permitted, enabled by the following masks.
4017 PNG_TRANSFORM_IDENTITY No transformation
4018 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
4019 PNG_TRANSFORM_PACKSWAP Change order of packed
4021 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
4022 PNG_TRANSFORM_SHIFT Normalize pixels to the
4024 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
4026 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
4028 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
4030 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
4031 PNG_TRANSFORM_STRIP_FILLER Strip out filler
4033 PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
4035 PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
4038 If you have valid image data in the info structure (you can use
4039 png_set_rows() to put image data in the info structure), simply do this:
4041 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
4043 where png_transforms is an integer containing the bitwise OR of some set of
4044 transformation flags. This call is equivalent to png_write_info(),
4045 followed the set of transformations indicated by the transform mask,
4046 then png_write_image(), and finally png_write_end().
4048 (The final parameter of this call is not yet used. Someday it might point
4049 to transformation parameters required by some future output transform.)
4051 You must use png_transforms and not call any png_set_transform() functions
4052 when you use png_write_png().
4054 .SS The low-level write interface
4056 If you are going the low-level route instead, you are now ready to
4057 write all the file information up to the actual image data. You do
4058 this with a call to png_write_info().
4060 png_write_info(png_ptr, info_ptr);
4062 Note that there is one transformation you may need to do before
4063 png_write_info(). In PNG files, the alpha channel in an image is the
4064 level of opacity. If your data is supplied as a level of transparency,
4065 you can invert the alpha channel before you write it, so that 0 is
4066 fully transparent and 255 (in 8-bit or paletted images) or 65535
4067 (in 16-bit images) is fully opaque, with
4069 png_set_invert_alpha(png_ptr);
4071 This must appear before png_write_info() instead of later with the
4072 other transformations because in the case of paletted images the tRNS
4073 chunk data has to be inverted before the tRNS chunk is written. If
4074 your image is not a paletted image, the tRNS data (which in such cases
4075 represents a single color to be rendered as transparent) won't need to
4076 be changed, and you can safely do this transformation after your
4077 png_write_info() call.
4079 If you need to write a private chunk that you want to appear before
4080 the PLTE chunk when PLTE is present, you can write the PNG info in
4081 two steps, and insert code to write your own chunk between them:
4083 png_write_info_before_PLTE(png_ptr, info_ptr);
4084 png_set_unknown_chunks(png_ptr, info_ptr, ...);
4085 png_write_info(png_ptr, info_ptr);
4087 After you've written the file information, you can set up the library
4088 to handle any special transformations of the image data. The various
4089 ways to transform the data will be described in the order that they
4090 should occur. This is important, as some of these change the color
4091 type and/or bit depth of the data, and some others only work on
4092 certain color types and bit depths. Even though each transformation
4093 checks to see if it has data that it can do something with, you should
4094 make sure to only enable a transformation if it will be valid for the
4095 data. For example, don't swap red and blue on grayscale data.
4097 PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
4098 the library to strip input data that has 4 or 8 bytes per pixel down
4099 to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
4102 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
4104 where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
4105 PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
4106 is stored XRGB or RGBX.
4108 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
4109 they can, resulting in, for example, 8 pixels per byte for 1 bit files.
4110 If the data is supplied at 1 pixel per byte, use this code, which will
4111 correctly pack the pixels into a single byte:
4113 png_set_packing(png_ptr);
4115 PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
4116 data is of another bit depth, you can write an sBIT chunk into the
4117 file so that decoders can recover the original data if desired.
4119 /* Set the true bit depth of the image data */
4120 if (color_type & PNG_COLOR_MASK_COLOR)
4122 sig_bit.red = true_bit_depth;
4123 sig_bit.green = true_bit_depth;
4124 sig_bit.blue = true_bit_depth;
4129 sig_bit.gray = true_bit_depth;
4132 if (color_type & PNG_COLOR_MASK_ALPHA)
4134 sig_bit.alpha = true_bit_depth;
4137 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
4139 If the data is stored in the row buffer in a bit depth other than
4140 one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
4141 this will scale the values to appear to be the correct bit depth as
4144 png_set_shift(png_ptr, &sig_bit);
4146 PNG files store 16-bit pixels in network byte order (big-endian,
4147 ie. most significant bits first). This code would be used if they are
4148 supplied the other way (little-endian, i.e. least significant bits
4149 first, the way PCs store them):
4152 png_set_swap(png_ptr);
4154 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
4155 need to change the order the pixels are packed into bytes, you can use:
4158 png_set_packswap(png_ptr);
4160 PNG files store 3 color pixels in red, green, blue order. This code
4161 would be used if they are supplied as blue, green, red:
4163 png_set_bgr(png_ptr);
4165 PNG files describe monochrome as black being zero and white being
4166 one. This code would be used if the pixels are supplied with this reversed
4167 (black being one and white being zero):
4169 png_set_invert_mono(png_ptr);
4171 Finally, you can write your own transformation function if none of
4172 the existing ones meets your needs. This is done by setting a callback
4175 png_set_write_user_transform_fn(png_ptr,
4176 write_transform_fn);
4178 You must supply the function
4180 void write_transform_fn(png_structp png_ptr, png_row_infop
4181 row_info, png_bytep data)
4183 See pngtest.c for a working example. Your function will be called
4184 before any of the other transformations are processed. If supported
4185 libpng also supplies an information routine that may be called from
4188 png_get_current_row_number(png_ptr);
4189 png_get_current_pass_number(png_ptr);
4191 This returns the current row passed to the transform. With interlaced
4192 images the value returned is the row in the input sub-image image. Use
4193 PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
4194 find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
4196 The discussion of interlace handling above contains more information on how to
4199 You can also set up a pointer to a user structure for use by your
4202 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
4204 The user_channels and user_depth parameters of this function are ignored
4205 when writing; you can set them to zero as shown.
4207 You can retrieve the pointer via the function png_get_user_transform_ptr().
4210 voidp write_user_transform_ptr =
4211 png_get_user_transform_ptr(png_ptr);
4213 It is possible to have libpng flush any pending output, either manually,
4214 or automatically after a certain number of lines have been written. To
4215 flush the output stream a single time call:
4217 png_write_flush(png_ptr);
4219 and to have libpng flush the output stream periodically after a certain
4220 number of scanlines have been written, call:
4222 png_set_flush(png_ptr, nrows);
4224 Note that the distance between rows is from the last time png_write_flush()
4225 was called, or the first row of the image if it has never been called.
4226 So if you write 50 lines, and then png_set_flush 25, it will flush the
4227 output on the next scanline, and every 25 lines thereafter, unless
4228 png_write_flush() is called before 25 more lines have been written.
4229 If nrows is too small (less than about 10 lines for a 640 pixel wide
4230 RGB image) the image compression may decrease noticeably (although this
4231 may be acceptable for real-time applications). Infrequent flushing will
4232 only degrade the compression performance by a few percent over images
4233 that do not use flushing.
4235 .SS Writing the image data
4237 That's it for the transformations. Now you can write the image data.
4238 The simplest way to do this is in one function call. If you have the
4239 whole image in memory, you can just call png_write_image() and libpng
4240 will write the image. You will need to pass in an array of pointers to
4241 each row. This function automatically handles interlacing, so you don't
4242 need to call png_set_interlace_handling() or call this function multiple
4243 times, or any of that other stuff necessary with png_write_rows().
4245 png_write_image(png_ptr, row_pointers);
4247 where row_pointers is:
4249 png_byte *row_pointers[height];
4251 You can point to void or char or whatever you use for pixels.
4253 If you don't want to write the whole image at once, you can
4254 use png_write_rows() instead. If the file is not interlaced,
4257 png_write_rows(png_ptr, row_pointers,
4260 row_pointers is the same as in the png_write_image() call.
4262 If you are just writing one row at a time, you can do this with
4263 a single row_pointer instead of an array of row_pointers:
4265 png_bytep row_pointer = row;
4267 png_write_row(png_ptr, row_pointer);
4269 When the file is interlaced, things can get a good deal more complicated.
4270 The only currently (as of the PNG Specification version 1.2, dated July
4271 1999) defined interlacing scheme for PNG files is the "Adam7" interlace
4272 scheme, that breaks down an image into seven smaller images of varying
4273 size. libpng will build these images for you, or you can do them
4274 yourself. If you want to build them yourself, see the PNG specification
4275 for details of which pixels to write when.
4277 If you don't want libpng to handle the interlacing details, just
4278 use png_set_interlace_handling() and call png_write_rows() the
4279 correct number of times to write all the sub-images
4280 (png_set_interlace_handling() returns the number of sub-images.)
4282 If you want libpng to build the sub-images, call this before you start
4285 number_of_passes = png_set_interlace_handling(png_ptr);
4287 This will return the number of passes needed. Currently, this is seven,
4288 but may change if another interlace type is added.
4290 Then write the complete image number_of_passes times.
4292 png_write_rows(png_ptr, row_pointers, number_of_rows);
4294 Think carefully before you write an interlaced image. Typically code that
4295 reads such images reads all the image data into memory, uncompressed, before
4296 doing any processing. Only code that can display an image on the fly can
4297 take advantage of the interlacing and even then the image has to be exactly
4298 the correct size for the output device, because scaling an image requires
4299 adjacent pixels and these are not available until all the passes have been
4302 If you do write an interlaced image you will hardly ever need to handle
4303 the interlacing yourself. Call png_set_interlace_handling() and use the
4304 approach described above.
4306 The only time it is conceivable that you will really need to write an
4307 interlaced image pass-by-pass is when you have read one pass by pass and
4308 made some pixel-by-pixel transformation to it, as described in the read
4309 code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros
4310 to determine the size of each sub-image in turn and simply write the rows
4311 you obtained from the read code.
4313 .SS Finishing a sequential write
4315 After you are finished writing the image, you should finish writing
4316 the file. If you are interested in writing comments or time, you should
4317 pass an appropriately filled png_info pointer. If you are not interested,
4320 png_write_end(png_ptr, info_ptr);
4322 When you are done, you can free all memory used by libpng like this:
4324 png_destroy_write_struct(&png_ptr, &info_ptr);
4326 It is also possible to individually free the info_ptr members that
4327 point to libpng-allocated storage with the following function:
4329 png_free_data(png_ptr, info_ptr, mask, seq)
4331 mask - identifies data to be freed, a mask
4332 containing the bitwise OR of one or
4334 PNG_FREE_PLTE, PNG_FREE_TRNS,
4335 PNG_FREE_HIST, PNG_FREE_ICCP,
4336 PNG_FREE_PCAL, PNG_FREE_ROWS,
4337 PNG_FREE_SCAL, PNG_FREE_SPLT,
4338 PNG_FREE_TEXT, PNG_FREE_UNKN,
4339 or simply PNG_FREE_ALL
4341 seq - sequence number of item to be freed
4344 This function may be safely called when the relevant storage has
4345 already been freed, or has not yet been allocated, or was allocated
4346 by the user and not by libpng, and will in those cases do nothing.
4347 The "seq" parameter is ignored if only one item of the selected data
4348 type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
4349 are allowed for the data type identified in the mask, such as text or
4350 sPLT, only the n'th item in the structure is freed, where n is "seq".
4352 If you allocated data such as a palette that you passed in to libpng
4353 with png_set_*, you must not free it until just before the call to
4354 png_destroy_write_struct().
4356 The default behavior is only to free data that was allocated internally
4357 by libpng. This can be changed, so that libpng will not free the data,
4358 or so that it will free data that was allocated by the user with png_malloc()
4359 or png_zalloc() and passed in via a png_set_*() function, with
4361 png_data_freer(png_ptr, info_ptr, freer, mask)
4364 PNG_DESTROY_WILL_FREE_DATA
4365 PNG_SET_WILL_FREE_DATA
4366 PNG_USER_WILL_FREE_DATA
4368 mask - which data elements are affected
4369 same choices as in png_free_data()
4371 For example, to transfer responsibility for some data from a read structure
4372 to a write structure, you could use
4374 png_data_freer(read_ptr, read_info_ptr,
4375 PNG_USER_WILL_FREE_DATA,
4376 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
4378 png_data_freer(write_ptr, write_info_ptr,
4379 PNG_DESTROY_WILL_FREE_DATA,
4380 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
4382 thereby briefly reassigning responsibility for freeing to the user but
4383 immediately afterwards reassigning it once more to the write_destroy
4384 function. Having done this, it would then be safe to destroy the read
4385 structure and continue to use the PLTE, tRNS, and hIST data in the write
4388 This function only affects data that has already been allocated.
4389 You can call this function before calling after the png_set_*() functions
4390 to control whether the user or png_destroy_*() is supposed to free the data.
4391 When the user assumes responsibility for libpng-allocated data, the
4392 application must use
4393 png_free() to free it, and when the user transfers responsibility to libpng
4394 for data that the user has allocated, the user must have used png_malloc()
4395 or png_zalloc() to allocate it.
4397 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
4398 separately, do not transfer responsibility for freeing text_ptr to libpng,
4399 because when libpng fills a png_text structure it combines these members with
4400 the key member, and png_free_data() will free only text_ptr.key. Similarly,
4401 if you transfer responsibility for free'ing text_ptr from libpng to your
4402 application, your application must not separately free those members.
4403 For a more compact example of writing a PNG image, see the file example.c.
4405 .SH V. Modifying/Customizing libpng:
4407 There are two issues here. The first is changing how libpng does
4408 standard things like memory allocation, input/output, and error handling.
4409 The second deals with more complicated things like adding new chunks,
4410 adding new transformations, and generally changing how libpng works.
4411 Both of those are compile-time issues; that is, they are generally
4412 determined at the time the code is written, and there is rarely a need
4413 to provide the user with a means of changing them.
4415 Memory allocation, input/output, and error handling
4417 All of the memory allocation, input/output, and error handling in libpng
4418 goes through callbacks that are user-settable. The default routines are
4419 in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
4420 these functions, call the appropriate png_set_*_fn() function.
4422 Memory allocation is done through the functions png_malloc(), png_calloc(),
4423 and png_free(). These currently just call the standard C functions.
4424 png_calloc() calls png_malloc() and then clears the newly
4425 allocated memory to zero. There is limited support for certain systems
4426 with segmented memory architectures and the types of pointers declared by
4427 png.h match this; you will have to use appropriate pointers in your
4428 application. Since it is
4429 unlikely that the method of handling memory allocation on a platform
4430 will change between applications, these functions must be modified in
4431 the library at compile time. If you prefer to use a different method
4432 of allocating and freeing data, you can use png_create_read_struct_2() or
4433 png_create_write_struct_2() to register your own functions as described
4434 above. These functions also provide a void pointer that can be retrieved
4437 mem_ptr=png_get_mem_ptr(png_ptr);
4439 Your replacement memory functions must have prototypes as follows:
4441 png_voidp malloc_fn(png_structp png_ptr,
4442 png_alloc_size_t size);
4444 void free_fn(png_structp png_ptr, png_voidp ptr);
4446 Your malloc_fn() must return NULL in case of failure. The png_malloc()
4447 function will normally call png_error() if it receives a NULL from the
4448 system memory allocator or from your replacement malloc_fn().
4450 Your free_fn() will never be called with a NULL ptr, since libpng's
4451 png_free() checks for NULL before calling free_fn().
4453 Input/Output in libpng is done through png_read() and png_write(),
4454 which currently just call fread() and fwrite(). The FILE * is stored in
4455 png_struct and is initialized via png_init_io(). If you wish to change
4456 the method of I/O, the library supplies callbacks that you can set
4457 through the function png_set_read_fn() and png_set_write_fn() at run
4458 time, instead of calling the png_init_io() function. These functions
4459 also provide a void pointer that can be retrieved via the function
4460 png_get_io_ptr(). For example:
4462 png_set_read_fn(png_structp read_ptr,
4463 voidp read_io_ptr, png_rw_ptr read_data_fn)
4465 png_set_write_fn(png_structp write_ptr,
4466 voidp write_io_ptr, png_rw_ptr write_data_fn,
4467 png_flush_ptr output_flush_fn);
4469 voidp read_io_ptr = png_get_io_ptr(read_ptr);
4470 voidp write_io_ptr = png_get_io_ptr(write_ptr);
4472 The replacement I/O functions must have prototypes as follows:
4474 void user_read_data(png_structp png_ptr,
4475 png_bytep data, png_size_t length);
4477 void user_write_data(png_structp png_ptr,
4478 png_bytep data, png_size_t length);
4480 void user_flush_data(png_structp png_ptr);
4482 The user_read_data() function is responsible for detecting and
4483 handling end-of-data errors.
4485 Supplying NULL for the read, write, or flush functions sets them back
4486 to using the default C stream functions, which expect the io_ptr to
4487 point to a standard *FILE structure. It is probably a mistake
4488 to use NULL for one of write_data_fn and output_flush_fn but not both
4489 of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
4490 It is an error to read from a write stream, and vice versa.
4492 Error handling in libpng is done through png_error() and png_warning().
4493 Errors handled through png_error() are fatal, meaning that png_error()
4494 should never return to its caller. Currently, this is handled via
4495 setjmp() and longjmp() (unless you have compiled libpng with
4496 PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()),
4497 but you could change this to do things like exit() if you should wish,
4498 as long as your function does not return.
4500 On non-fatal errors, png_warning() is called
4501 to print a warning message, and then control returns to the calling code.
4502 By default png_error() and png_warning() print a message on stderr via
4503 fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
4504 (because you don't want the messages) or PNG_NO_STDIO defined (because
4505 fprintf() isn't available). If you wish to change the behavior of the error
4506 functions, you will need to set up your own message callbacks. These
4507 functions are normally supplied at the time that the png_struct is created.
4508 It is also possible to redirect errors and warnings to your own replacement
4509 functions after png_create_*_struct() has been called by calling:
4511 png_set_error_fn(png_structp png_ptr,
4512 png_voidp error_ptr, png_error_ptr error_fn,
4513 png_error_ptr warning_fn);
4515 png_voidp error_ptr = png_get_error_ptr(png_ptr);
4517 If NULL is supplied for either error_fn or warning_fn, then the libpng
4518 default function will be used, calling fprintf() and/or longjmp() if a
4519 problem is encountered. The replacement error functions should have
4520 parameters as follows:
4522 void user_error_fn(png_structp png_ptr,
4523 png_const_charp error_msg);
4525 void user_warning_fn(png_structp png_ptr,
4526 png_const_charp warning_msg);
4528 The motivation behind using setjmp() and longjmp() is the C++ throw and
4529 catch exception handling methods. This makes the code much easier to write,
4530 as there is no need to check every return code of every function call.
4531 However, there are some uncertainties about the status of local variables
4532 after a longjmp, so the user may want to be careful about doing anything
4533 after setjmp returns non-zero besides returning itself. Consult your
4534 compiler documentation for more details. For an alternative approach, you
4535 may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net),
4536 which is illustrated in pngvalid.c and in contrib/visupng.
4540 If you need to read or write custom chunks, you may need to get deeper
4541 into the libpng code. The library now has mechanisms for storing
4542 and writing chunks of unknown type; you can even declare callbacks
4543 for custom chunks. However, this may not be good enough if the
4544 library code itself needs to know about interactions between your
4545 chunk and existing `intrinsic' chunks.
4547 If you need to write a new intrinsic chunk, first read the PNG
4548 specification. Acquire a first level of understanding of how it works.
4549 Pay particular attention to the sections that describe chunk names,
4550 and look at how other chunks were designed, so you can do things
4551 similarly. Second, check out the sections of libpng that read and
4552 write chunks. Try to find a chunk that is similar to yours and use
4553 it as a template. More details can be found in the comments inside
4554 the code. It is best to handle private or unknown chunks in a generic method,
4555 via callback functions, instead of by modifying libpng functions. This
4556 is illustrated in pngtest.c, which uses a callback function to handle a
4557 private "vpAg" chunk and the new "sTER" chunk, which are both unknown to
4560 If you wish to write your own transformation for the data, look through
4561 the part of the code that does the transformations, and check out some of
4562 the simpler ones to get an idea of how they work. Try to find a similar
4563 transformation to the one you want to add and copy off of it. More details
4564 can be found in the comments inside the code itself.
4566 .SS Configuring for 16-bit platforms
4568 You will want to look into zconf.h to tell zlib (and thus libpng) that
4569 it cannot allocate more then 64K at a time. Even if you can, the memory
4570 won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
4572 .SS Configuring for DOS
4574 For DOS users who only have access to the lower 640K, you will
4575 have to limit zlib's memory usage via a png_set_compression_mem_level()
4576 call. See zlib.h or zconf.h in the zlib library for more information.
4578 .SS Configuring for Medium Model
4580 Libpng's support for medium model has been tested on most of the popular
4581 compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
4582 defined, and FAR gets defined to far in pngconf.h, and you should be
4583 all set. Everything in the library (except for zlib's structure) is
4584 expecting far data. You must use the typedefs with the p or pp on
4585 the end for pointers (or at least look at them and be careful). Make
4586 note that the rows of data are defined as png_bytepp, which is
4587 an "unsigned char far * far *".
4589 .SS Configuring for gui/windowing platforms:
4591 You will need to write new error and warning functions that use the GUI
4592 interface, as described previously, and set them to be the error and
4593 warning functions at the time that png_create_*_struct() is called,
4594 in order to have them available during the structure initialization.
4595 They can be changed later via png_set_error_fn(). On some compilers,
4596 you may also have to change the memory allocators (png_malloc, etc.).
4598 .SS Configuring for compiler xxx:
4600 All includes for libpng are in pngconf.h. If you need to add, change
4601 or delete an include, this is the place to do it.
4602 The includes that are not needed outside libpng are placed in pngpriv.h,
4603 which is only used by the routines inside libpng itself.
4604 The files in libpng proper only include pngpriv.h and png.h, which
4605 %14%in turn includes pngconf.h.
4606 in turn includes pngconf.h and, as of libpng-1.5.0, pnglibconf.h.
4607 As of libpng-1.5.0, pngpriv.h also includes three other private header
4608 files, pngstruct.h, pnginfo.h, and pngdebug.h, which contain material
4609 that previously appeared in the public headers.
4611 .SS Configuring zlib:
4613 There are special functions to configure the compression. Perhaps the
4614 most useful one changes the compression level, which currently uses
4615 input compression values in the range 0 - 9. The library normally
4616 uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
4617 have shown that for a large majority of images, compression values in
4618 the range 3-6 compress nearly as well as higher levels, and do so much
4619 faster. For online applications it may be desirable to have maximum speed
4620 (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
4621 specify no compression (Z_NO_COMPRESSION = 0), but this would create
4622 files larger than just storing the raw bitmap. You can specify the
4623 compression level by calling:
4626 png_set_compression_level(png_ptr, level);
4628 Another useful one is to reduce the memory level used by the library.
4629 The memory level defaults to 8, but it can be lowered if you are
4630 short on memory (running DOS, for example, where you only have 640K).
4631 Note that the memory level does have an effect on compression; among
4632 other things, lower levels will result in sections of incompressible
4633 data being emitted in smaller stored blocks, with a correspondingly
4634 larger relative overhead of up to 15% in the worst case.
4637 png_set_compression_mem_level(png_ptr, level);
4639 The other functions are for configuring zlib. They are not recommended
4640 for normal use and may result in writing an invalid PNG file. See
4641 zlib.h for more information on what these mean.
4644 png_set_compression_strategy(png_ptr,
4647 png_set_compression_window_bits(png_ptr,
4650 png_set_compression_method(png_ptr, method);
4652 png_set_compression_buffer_size(png_ptr, size);
4654 As of libpng version 1.5.4, additional APIs became
4655 available to set these separately for non-IDAT
4656 compressed chunks such as zTXt, iTXt, and iCCP:
4659 #if PNG_LIBPNG_VER <= 10504
4660 png_set_text_compression_level(png_ptr, level);
4662 png_set_text_compression_mem_level(png_ptr, level);
4664 png_set_text_compression_strategy(png_ptr,
4667 png_set_text_compression_window_bits(png_ptr,
4670 png_set_text_compression_method(png_ptr, method);
4673 .SS Controlling row filtering
4675 If you want to control whether libpng uses filtering or not, which
4676 filters are used, and how it goes about picking row filters, you
4677 can call one of these functions. The selection and configuration
4678 of row filters can have a significant impact on the size and
4679 encoding speed and a somewhat lesser impact on the decoding speed
4680 of an image. Filtering is enabled by default for RGB and grayscale
4681 images (with and without alpha), but not for paletted images nor
4682 for any images with bit depths less than 8 bits/pixel.
4684 The 'method' parameter sets the main filtering method, which is
4685 currently only '0' in the PNG 1.2 specification. The 'filters'
4686 parameter sets which filter(s), if any, should be used for each
4687 scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
4688 to turn filtering on and off, respectively.
4690 Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
4691 PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
4692 ORed together with '|' to specify one or more filters to use.
4693 These filters are described in more detail in the PNG specification.
4694 If you intend to change the filter type during the course of writing
4695 the image, you should start with flags set for all of the filters
4696 you intend to use so that libpng can initialize its internal
4697 structures appropriately for all of the filter types. (Note that this
4698 means the first row must always be adaptively filtered, because libpng
4699 currently does not allocate the filter buffers until png_write_row()
4700 is called for the first time.)
4702 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
4703 PNG_FILTER_UP | PNG_FILTER_AVG |
4704 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
4706 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
4708 The second parameter can also be
4709 PNG_INTRAPIXEL_DIFFERENCING if you are
4710 writing a PNG to be embedded in a MNG
4711 datastream. This parameter must be the
4712 same as the value of filter_method used
4715 It is also possible to influence how libpng chooses from among the
4716 available filters. This is done in one or both of two ways - by
4717 telling it how important it is to keep the same filter for successive
4718 rows, and by telling it the relative computational costs of the filters.
4720 double weights[3] = {1.5, 1.3, 1.1},
4721 costs[PNG_FILTER_VALUE_LAST] =
4722 {1.0, 1.3, 1.3, 1.5, 1.7};
4724 png_set_filter_heuristics(png_ptr,
4725 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
4728 The weights are multiplying factors that indicate to libpng that the
4729 row filter should be the same for successive rows unless another row filter
4730 is that many times better than the previous filter. In the above example,
4731 if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
4732 "sum of absolute differences" 1.5 x 1.3 times higher than other filters
4733 and still be chosen, while the NONE filter could have a sum 1.1 times
4734 higher than other filters and still be chosen. Unspecified weights are
4735 taken to be 1.0, and the specified weights should probably be declining
4736 like those above in order to emphasize recent filters over older filters.
4738 The filter costs specify for each filter type a relative decoding cost
4739 to be considered when selecting row filters. This means that filters
4740 with higher costs are less likely to be chosen over filters with lower
4741 costs, unless their "sum of absolute differences" is that much smaller.
4742 The costs do not necessarily reflect the exact computational speeds of
4743 the various filters, since this would unduly influence the final image
4746 Note that the numbers above were invented purely for this example and
4747 are given only to help explain the function usage. Little testing has
4748 been done to find optimum values for either the costs or the weights.
4750 .SS Removing unwanted object code
4752 There are a bunch of #define's in pngconf.h that control what parts of
4753 libpng are compiled. All the defines end in _SUPPORTED. If you are
4754 never going to use a capability, you can change the #define to #undef
4755 before recompiling libpng and save yourself code and data space, or
4756 you can turn off individual capabilities with defines that begin with
4759 In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead.
4761 You can also turn all of the transforms and ancillary chunk capabilities
4762 off en masse with compiler directives that define
4763 PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
4765 along with directives to turn on any of the capabilities that you do
4766 want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra
4767 transformations but still leave the library fully capable of reading
4768 and writing PNG files with all known public chunks. Use of the
4769 PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library
4770 that is incapable of reading or writing ancillary chunks. If you are
4771 not using the progressive reading capability, you can turn that off
4772 with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING
4773 capability, which you'll still have).
4775 All the reading and writing specific code are in separate files, so the
4776 linker should only grab the files it needs. However, if you want to
4777 make sure, or if you are building a stand alone library, all the
4778 reading files start with "pngr" and all the writing files start with "pngw".
4779 The files that don't match either (like png.c, pngtrans.c, etc.)
4780 are used for both reading and writing, and always need to be included.
4781 The progressive reader is in pngpread.c
4783 If you are creating or distributing a dynamically linked library (a .so
4784 or DLL file), you should not remove or disable any parts of the library,
4785 as this will cause applications linked with different versions of the
4786 library to fail if they call functions not available in your library.
4787 The size of the library itself should not be an issue, because only
4788 those sections that are actually used will be loaded into memory.
4790 .SS Requesting debug printout
4792 The macro definition PNG_DEBUG can be used to request debugging
4793 printout. Set it to an integer value in the range 0 to 3. Higher
4794 numbers result in increasing amounts of debugging information. The
4795 information is printed to the "stderr" file, unless another file
4796 name is specified in the PNG_DEBUG_FILE macro definition.
4798 When PNG_DEBUG > 0, the following functions (macros) become available:
4800 png_debug(level, message)
4801 png_debug1(level, message, p1)
4802 png_debug2(level, message, p1, p2)
4804 in which "level" is compared to PNG_DEBUG to decide whether to print
4805 the message, "message" is the formatted string to be printed,
4806 and p1 and p2 are parameters that are to be embedded in the string
4807 according to printf-style formatting directives. For example,
4809 png_debug1(2, "foo=%d\n", foo);
4814 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
4816 When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
4817 can still use PNG_DEBUG to control your own debugging:
4823 When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
4824 having level = 0 will be printed. There aren't any such statements in
4825 this version of libpng, but if you insert some they will be printed.
4829 The MNG specification (available at http://www.libpng.org/pub/mng) allows
4830 certain extensions to PNG for PNG images that are embedded in MNG datastreams.
4831 Libpng can support some of these extensions. To enable them, use the
4832 png_permit_mng_features() function:
4834 feature_set = png_permit_mng_features(png_ptr, mask)
4836 mask is a png_uint_32 containing the bitwise OR of the
4837 features you want to enable. These include
4838 PNG_FLAG_MNG_EMPTY_PLTE
4839 PNG_FLAG_MNG_FILTER_64
4840 PNG_ALL_MNG_FEATURES
4842 feature_set is a png_uint_32 that is the bitwise AND of
4843 your mask with the set of MNG features that is
4844 supported by the version of libpng that you are using.
4846 It is an error to use this function when reading or writing a standalone
4847 PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
4848 in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
4849 and the MHDR and MEND chunks. Libpng does not provide support for these
4850 or any other MNG chunks; your application must provide its own support for
4851 them. You may wish to consider using libmng (available at
4852 http://www.libmng.com) instead.
4854 .SH VII. Changes to Libpng from version 0.88
4856 It should be noted that versions of libpng later than 0.96 are not
4857 distributed by the original libpng author, Guy Schalnat, nor by
4858 Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
4859 distributed versions 0.89 through 0.96, but rather by another member
4860 of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
4861 still alive and well, but they have moved on to other things.
4863 The old libpng functions png_read_init(), png_write_init(),
4864 png_info_init(), png_read_destroy(), and png_write_destroy() have been
4865 moved to PNG_INTERNAL in version 0.95 to discourage their use. These
4866 functions will be removed from libpng version 1.4.0.
4868 The preferred method of creating and initializing the libpng structures is
4869 via the png_create_read_struct(), png_create_write_struct(), and
4870 png_create_info_struct() because they isolate the size of the structures
4871 from the application, allow version error checking, and also allow the
4872 use of custom error handling routines during the initialization, which
4873 the old functions do not. The functions png_read_destroy() and
4874 png_write_destroy() do not actually free the memory that libpng
4875 allocated for these structs, but just reset the data structures, so they
4876 can be used instead of png_destroy_read_struct() and
4877 png_destroy_write_struct() if you feel there is too much system overhead
4878 allocating and freeing the png_struct for each image read.
4880 Setting the error callbacks via png_set_message_fn() before
4881 png_read_init() as was suggested in libpng-0.88 is no longer supported
4882 because this caused applications that do not use custom error functions
4883 to fail if the png_ptr was not initialized to zero. It is still possible
4884 to set the error callbacks AFTER png_read_init(), or to change them with
4885 png_set_error_fn(), which is essentially the same function, but with a new
4886 name to force compilation errors with applications that try to use the old
4889 Starting with version 1.0.7, you can find out which version of the library
4890 you are using at run-time:
4892 png_uint_32 libpng_vn = png_access_version_number();
4894 The number libpng_vn is constructed from the major version, minor
4895 version with leading zero, and release number with leading zero,
4896 (e.g., libpng_vn for version 1.0.7 is 10007).
4898 Note that this function does not take a png_ptr, so you can call it
4899 before you've created one.
4901 You can also check which version of png.h you used when compiling your
4904 png_uint_32 application_vn = PNG_LIBPNG_VER;
4906 .SH VIII. Changes to Libpng from version 1.0.x to 1.2.x
4908 Support for user memory management was enabled by default. To
4909 accomplish this, the functions png_create_read_struct_2(),
4910 png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
4911 png_malloc_default(), and png_free_default() were added.
4913 Support for the iTXt chunk has been enabled by default as of
4916 Support for certain MNG features was enabled.
4918 Support for numbered error messages was added. However, we never got
4919 around to actually numbering the error messages. The function
4920 png_set_strip_error_numbers() was added (Note: the prototype for this
4921 function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
4922 builds of libpng-1.2.15. It was restored in libpng-1.2.36).
4924 The png_malloc_warn() function was added at libpng-1.2.3. This issues
4925 a png_warning and returns NULL instead of aborting when it fails to
4926 acquire the requested memory allocation.
4928 Support for setting user limits on image width and height was enabled
4929 by default. The functions png_set_user_limits(), png_get_user_width_max(),
4930 and png_get_user_height_max() were added at libpng-1.2.6.
4932 The png_set_add_alpha() function was added at libpng-1.2.7.
4934 The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
4935 Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
4936 tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
4939 A number of macro definitions in support of runtime selection of
4940 assembler code features (especially Intel MMX code support) were
4941 added at libpng-1.2.0:
4943 PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
4944 PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
4945 PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
4946 PNG_ASM_FLAG_MMX_READ_INTERLACE
4947 PNG_ASM_FLAG_MMX_READ_FILTER_SUB
4948 PNG_ASM_FLAG_MMX_READ_FILTER_UP
4949 PNG_ASM_FLAG_MMX_READ_FILTER_AVG
4950 PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
4951 PNG_ASM_FLAGS_INITIALIZED
4957 We added the following functions in support of runtime
4958 selection of assembler code features:
4960 png_get_mmx_flagmask()
4961 png_set_mmx_thresholds()
4963 png_get_mmx_bitdepth_threshold()
4964 png_get_mmx_rowbytes_threshold()
4967 We replaced all of these functions with simple stubs in libpng-1.2.20,
4968 when the Intel assembler code was removed due to a licensing issue.
4970 These macros are deprecated:
4972 PNG_READ_TRANSFORMS_NOT_SUPPORTED
4973 PNG_PROGRESSIVE_READ_NOT_SUPPORTED
4974 PNG_NO_SEQUENTIAL_READ_SUPPORTED
4975 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
4976 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
4977 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
4979 They have been replaced, respectively, by:
4981 PNG_NO_READ_TRANSFORMS
4982 PNG_NO_PROGRESSIVE_READ
4983 PNG_NO_SEQUENTIAL_READ
4984 PNG_NO_WRITE_TRANSFORMS
4985 PNG_NO_READ_ANCILLARY_CHUNKS
4986 PNG_NO_WRITE_ANCILLARY_CHUNKS
4988 PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
4989 deprecated since libpng-1.0.16 and libpng-1.2.6.
4992 png_check_sig(sig, num)
4994 !png_sig_cmp(sig, 0, num)
4995 It has been deprecated since libpng-0.90.
4998 png_set_gray_1_2_4_to_8()
4999 which also expands tRNS to alpha was replaced with
5000 png_set_expand_gray_1_2_4_to_8()
5001 which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
5003 .SH IX. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
5005 Private libpng prototypes and macro definitions were moved from
5006 png.h and pngconf.h into a new pngpriv.h header file.
5008 Functions png_set_benign_errors(), png_benign_error(), and
5009 png_chunk_benign_error() were added.
5011 Support for setting the maximum amount of memory that the application
5012 will allocate for reading chunks was added, as a security measure.
5013 The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()
5014 were added to the library.
5016 We implemented support for I/O states by adding png_ptr member io_state
5017 and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
5019 We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level
5022 Checking for and reporting of errors in the IHDR chunk is more thorough.
5024 Support for global arrays was removed, to improve thread safety.
5026 Some obsolete/deprecated macros and functions have been removed.
5028 Typecasted NULL definitions such as
5029 #define png_voidp_NULL (png_voidp)NULL
5030 were eliminated. If you used these in your application, just use
5033 The png_struct and info_struct members "trans" and "trans_values" were
5034 changed to "trans_alpha" and "trans_color", respectively.
5036 The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles
5039 The PNG_1_0_X and PNG_1_2_X macros were eliminated.
5041 The PNG_LEGACY_SUPPORTED macro was eliminated.
5043 Many WIN32_WCE #ifdefs were removed.
5045 The functions png_read_init(info_ptr), png_write_init(info_ptr),
5046 png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
5047 have been removed. They have been deprecated since libpng-0.95.
5049 The png_permit_empty_plte() was removed. It has been deprecated
5050 since libpng-1.0.9. Use png_permit_mng_features() instead.
5052 We removed the obsolete stub functions png_get_mmx_flagmask(),
5053 png_set_mmx_thresholds(), png_get_asm_flags(),
5054 png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
5055 png_set_asm_flags(), and png_mmx_supported()
5057 We removed the obsolete png_check_sig(), png_memcpy_check(), and
5058 png_memset_check() functions. Instead use !png_sig_cmp(), memcpy(),
5059 and memset(), respectively.
5061 The function png_set_gray_1_2_4_to_8() was removed. It has been
5062 deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
5063 png_set_expand_gray_1_2_4_to_8() because the former function also
5064 expanded any tRNS chunk to an alpha channel.
5066 Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32
5067 were added and are used by default instead of the corresponding
5068 functions. Unfortunately,
5069 from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5070 function) incorrectly returned a value of type png_uint_32.
5072 We changed the prototype for png_malloc() from
5073 png_malloc(png_structp png_ptr, png_uint_32 size)
5075 png_malloc(png_structp png_ptr, png_alloc_size_t size)
5077 This also applies to the prototype for the user replacement malloc_fn().
5079 The png_calloc() function was added and is used in place of
5080 of "png_malloc(); memset();" except in the case in png_read_png()
5081 where the array consists of pointers; in this case a "for" loop is used
5082 after the png_malloc() to set the pointers to NULL, to give robust.
5083 behavior in case the application runs out of memory part-way through
5086 We changed the prototypes of png_get_compression_buffer_size() and
5087 png_set_compression_buffer_size() to work with png_size_t instead of
5090 Support for numbered error messages was removed by default, since we
5091 never got around to actually numbering the error messages. The function
5092 png_set_strip_error_numbers() was removed from the library by default.
5094 The png_zalloc() and png_zfree() functions are no longer exported.
5095 The png_zalloc() function no longer zeroes out the memory that it
5098 Support for dithering was disabled by default in libpng-1.4.0, because
5099 it has not been well tested and doesn't actually "dither".
5101 removed, however, and could be enabled by building libpng with
5102 PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
5103 was reenabled, but the function was renamed png_set_quantize() to
5104 reflect more accurately what it actually does. At the same time,
5105 the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
5106 PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED
5107 was renamed to PNG_READ_QUANTIZE_SUPPORTED.
5109 We removed the trailing '.' from the warning and error messages.
5111 .SH X. Changes to Libpng from version 1.4.x to 1.5.x
5113 From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5114 function) incorrectly returned a value of type png_uint_32.
5116 A. Changes that affect users of libpng
5118 There are no substantial API changes between the non-deprecated parts of
5119 the 1.4.5 API and the 1.5.0 API, however the ability to directly access
5120 the main libpng control structures, png_struct and png_info, deprecated
5121 in earlier versions of libpng, has been completely removed from
5124 We no longer include zlib.h in png.h. Applications that need access
5125 to information in zlib.h will need to add the '#include "zlib.h"'
5126 directive. It does not matter whether it is placed prior to or after
5127 the '"#include png.h"' directive.
5129 We moved the png_strcpy(), png_strncpy(), png_strlen(), png_memcpy(),
5130 png_memcmp(), png_sprintf, and png_memcpy() macros into a private
5131 header file (pngpriv.h) that is not accessible to applications.
5133 In png_get_iCCP, the type of "profile" was changed from png_charpp
5134 to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
5136 There are changes of form in png.h, including new and changed macros to
5137 declare parts of the API. Some API functions with arguments that are
5138 pointers to data not modified within the function have been corrected to
5139 declare these arguments with PNG_CONST.
5141 Much of the internal use of C macros to control the library build has also
5142 changed and some of this is visible in the exported header files, in
5143 particular the use of macros to control data and API elements visible
5144 during application compilation may require significant revision to
5145 application code. (It is extremely rare for an application to do this.)
5147 Any program that compiled against libpng 1.4 and did not use deprecated
5148 features or access internal library structures should compile and work
5149 against libpng 1.5, except for the change in the prototype for
5150 png_get_iCCP() and png_set_iCCP() API functions mentioned above.
5152 libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of
5153 interlaced images. The macros return the number of rows and columns in
5154 each pass and information that can be used to de-interlace and (if
5155 absolutely necessary) interlace an image.
5157 libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls
5158 the application-provided png_longjmp_ptr on the internal, but application
5159 initialized, longjmp buffer. It is provided as a convenience to avoid
5160 the need to use the png_jmpbuf macro, which had the unnecessary side
5161 effect of resetting the internal png_longjmp_ptr value.
5163 libpng 1.5.0 includes a complete fixed point API. By default this is
5164 present along with the corresponding floating point API. In general the
5165 fixed point API is faster and smaller than the floating point one because
5166 the PNG file format used fixed point, not floating point. This applies
5167 even if the library uses floating point in internal calculations. A new
5168 macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library
5169 uses floating point arithmetic (the default) or fixed point arithmetic
5170 internally for performance critical calculations such as gamma correction.
5171 In some cases, the gamma calculations may produce slightly different
5172 results. This has changed the results in png_rgb_to_gray and in alpha
5173 composition (png_set_background for example). This applies even if the
5174 original image was already linear (gamma == 1.0) and, therefore, it is
5175 not necessary to linearize the image. This is because libpng has *not*
5176 been changed to optimize that case correctly, yet.
5178 Fixed point support for the sCAL chunk comes with an important caveat;
5179 the sCAL specification uses a decimal encoding of floating point values
5180 and the accuracy of PNG fixed point values is insufficient for
5181 representation of these values. Consequently a "string" API
5182 (png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading
5183 arbitrary sCAL chunks in the absence of either the floating point API or
5184 internal floating point calculations.
5186 Applications no longer need to include the optional distribution header
5187 file pngusr.h or define the corresponding macros during application
5188 build in order to see the correct variant of the libpng API. From 1.5.0
5189 application code can check for the corresponding _SUPPORTED macro:
5191 #ifdef PNG_INCH_CONVERSIONS_SUPPORTED
5192 /* code that uses the inch conversion APIs. */
5195 This macro will only be defined if the inch conversion functions have been
5196 compiled into libpng. The full set of macros, and whether or not support
5197 has been compiled in, are available in the header file pnglibconf.h.
5198 This header file is specific to the libpng build. Notice that prior to
5199 1.5.0 the _SUPPORTED macros would always have the default definition unless
5200 reset by pngusr.h or by explicit settings on the compiler command line.
5201 These settings may produce compiler warnings or errors in 1.5.0 because
5202 of macro redefinition.
5204 From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5205 function) incorrectly returned a value of type png_uint_32. libpng 1.5.0
5206 is consistent with the implementation in 1.4.5 and 1.2.x (where the macro
5209 Applications can now choose whether to use these macros or to call the
5210 corresponding function by defining PNG_USE_READ_MACROS or
5211 PNG_NO_USE_READ_MACROS before including png.h. Notice that this is
5212 only supported from 1.5.0 -defining PNG_NO_USE_READ_MACROS prior to 1.5.0
5213 will lead to a link failure.
5215 Prior to libpng-1.5.4, the zlib compressor used the same set of parameters
5216 when compressing the IDAT data and textual data such as zTXt and iCCP.
5217 In libpng-1.5.4 we reinitialized the zlib stream for each type of data.
5218 We added five png_set_text_*() functions for setting the parameters to
5219 use with textual data.
5221 Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
5222 option was off by default, and slightly inaccurate scaling occurred.
5223 This option can no longer be turned off, and the choice of accurate
5224 or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8()
5225 API for accurate scaling or the old png_set_strip_16_to_8() API for simple
5228 Prior to libpng-1.5.4, the png_set_user_limits() function could only be
5229 used to reduce the width and height limits from the value of
5230 PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said
5231 that it could be used to override them. Now this function will reduce or
5232 increase the limits.
5234 B. Changes to the build and configuration of libpng
5236 Details of internal changes to the library code can be found in the CHANGES
5237 file and in the GIT repository logs. These will be of no concern to the vast
5238 majority of library users or builders, however the few who configure libpng
5239 to a non-default feature set may need to change how this is done.
5241 There should be no need for library builders to alter build scripts if
5242 these use the distributed build support - configure or the makefiles -
5243 however users of the makefiles may care to update their build scripts
5244 to build pnglibconf.h where the corresponding makefile does not do so.
5246 Building libpng with a non-default configuration has changed completely.
5247 The old method using pngusr.h should still work correctly even though the
5248 way pngusr.h is used in the build has been changed; however, library
5249 builders will probably want to examine the changes to take advantage of
5250 new capabilities and to simplify their build system.
5252 B.1 Specific changes to library configuration capabilities
5254 The library now supports a complete fixed point implementation and can
5255 thus be used on systems that have no floating point support or very
5256 limited or slow support. Previously gamma correction, an essential part
5257 of complete PNG support, required reasonably fast floating point.
5259 As part of this the choice of internal implementation has been made
5260 independent of the choice of fixed versus floating point APIs and all the
5261 missing fixed point APIs have been implemented.
5263 The exact mechanism used to control attributes of API functions has
5264 changed. A single set of operating system independent macro definitions
5265 is used and operating system specific directives are defined in
5268 As part of this the mechanism used to choose procedure call standards on
5269 those systems that allow a choice has been changed. At present this only
5270 affects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systems
5271 running on Intel processors. As before, PNGAPI is defined where required
5272 to control the exported API functions; however, two new macros, PNGCBAPI
5273 and PNGCAPI, are used instead for callback functions (PNGCBAPI) and
5274 (PNGCAPI) for functions that must match a C library prototype (currently
5275 only png_longjmp_ptr, which must match the C longjmp function.) The new
5276 approach is documented in pngconf.h
5278 Despite these changes, libpng 1.5.0 only supports the native C function
5279 calling standard on those platforms tested so far (__cdecl on Microsoft
5280 Windows). This is because the support requirements for alternative
5281 calling conventions seem to no longer exist. Developers who find it
5282 necessary to set PNG_API_RULE to 1 should advise the mailing list
5283 (png-mng-implement) of this and library builders who use Openwatcom and
5284 therefore set PNG_API_RULE to 2 should also contact the mailing list.
5286 A new test program, pngvalid, is provided in addition to pngtest.
5287 pngvalid validates the arithmetic accuracy of the gamma correction
5288 calculations and includes a number of validations of the file format.
5289 A subset of the full range of tests is run when "make check" is done
5290 (in the 'configure' build.) pngvalid also allows total allocated memory
5291 usage to be evaluated and performs additional memory overwrite validation.
5293 Many changes to individual feature macros have been made. The following
5294 are the changes most likely to be noticed by library builders who
5297 1) All feature macros now have consistent naming:
5299 #define PNG_NO_feature turns the feature off
5300 #define PNG_feature_SUPPORTED turns the feature on
5302 pnglibconf.h contains one line for each feature macro which is either:
5304 #define PNG_feature_SUPPORTED
5306 if the feature is supported or:
5308 /*#undef PNG_feature_SUPPORTED*/
5310 if it is not. Library code consistently checks for the 'SUPPORTED' macro.
5311 It does not, and libpng applications should not, check for the 'NO' macro
5312 which will not normally be defined even if the feature is not supported.
5313 The 'NO' macros are only used internally for setting or not setting the
5314 corresponding 'SUPPORTED' macros.
5316 Compatibility with the old names is provided as follows:
5318 PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
5320 And the following definitions disable the corresponding feature:
5322 PNG_SETJMP_NOT_SUPPORTED disables SETJMP
5323 PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS
5324 PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV
5325 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS
5326 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS
5327 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
5329 Library builders should remove use of the above, inconsistent, names.
5331 2) Warning and error message formatting was previously conditional on
5332 the STDIO feature. The library has been changed to use the
5333 CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled
5334 the library no longer uses the printf(3) functions, even though the
5335 default read/write implementations use (FILE) style stdio.h functions.
5337 3) Three feature macros now control the fixed/floating point decisions:
5339 PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
5341 PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in
5342 practice these are normally required internally anyway (because the PNG
5343 file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT
5344 merely stops the function from being exported.
5346 PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating
5347 point implementation or the fixed point one. Typically the fixed point
5348 implementation is larger and slower than the floating point implementation
5349 on a system that supports floating point, however it may be faster on a
5350 system which lacks floating point hardware and therefore uses a software
5353 4) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the
5354 functions to read and write ints to be disabled independently of
5355 PNG_USE_READ_MACROS, which allows libpng to be built with the functions
5356 even though the default is to use the macros - this allows applications
5357 to choose at app buildtime whether or not to use macros (previously
5358 impossible because the functions weren't in the default build.)
5360 B.2 Changes to the configuration mechanism
5362 Prior to libpng-1.5.0 library builders who needed to configure libpng
5363 had either to modify the exported pngconf.h header file to add system
5364 specific configuration or had to write feature selection macros into
5365 pngusr.h and cause this to be included into pngconf.h by defining
5366 PNG_USER_CONFIG. The latter mechanism had the disadvantage that an
5367 application built without PNG_USER_CONFIG defined would see the
5368 unmodified, default, libpng API and thus would probably fail to link.
5370 These mechanisms still work in the configure build and in any makefile
5371 build that builds pnglibconf.h, although the feature selection macros
5372 have changed somewhat as described above. In 1.5.0, however, pngusr.h is
5373 processed only once, when the exported header file pnglibconf.h is built.
5374 pngconf.h no longer includes pngusr.h, therefore pngusr.h is ignored after the
5375 build of pnglibconf.h and it is never included in an application build.
5377 The rarely used alternative of adding a list of feature macros to the
5378 CFLAGS setting in the build also still works, however the macros will be
5379 copied to pnglibconf.h and this may produce macro redefinition warnings
5380 when the individual C files are compiled.
5382 All configuration now only works if pnglibconf.h is built from
5383 scripts/pnglibconf.dfa. This requires the program awk. Brian Kernighan
5384 (the original author of awk) maintains C source code of that awk and this
5385 and all known later implementations (often called by subtly different
5386 names - nawk and gawk for example) are adequate to build pnglibconf.h.
5387 The Sun Microsystems (now Oracle) program 'awk' is an earlier version
5388 and does not work; this may also apply to other systems that have a
5389 functioning awk called 'nawk'.
5391 Configuration options are now documented in scripts/pnglibconf.dfa. This
5392 file also includes dependency information that ensures a configuration is
5393 consistent; that is, if a feature is switched off dependent features are
5394 also removed. As a recommended alternative to using feature macros in
5395 pngusr.h a system builder may also define equivalent options in pngusr.dfa
5396 (or, indeed, any file) and add that to the configuration by setting
5397 DFA_XTRA to the file name. The makefiles in contrib/pngminim illustrate
5398 how to do this, and a case where pngusr.h is still required.
5400 .SH XI. Detecting libpng
5402 The png_get_io_ptr() function has been present since libpng-0.88, has never
5403 changed, and is unaffected by conditional compilation macros. It is the
5404 best choice for use in configure scripts for detecting the presence of any
5405 libpng version since 0.88. In an autoconf "configure.in" you could use
5407 AC_CHECK_LIB(png, png_get_io_ptr, ...
5409 .SH XII. Source code repository
5411 Since about February 2009, version 1.2.34, libpng has been under "git" source
5412 control. The git repository was built from old libpng-x.y.z.tar.gz files
5413 going back to version 0.70. You can access the git repository (read only)
5416 git://libpng.git.sourceforge.net/gitroot/libpng
5418 or you can browse it via "gitweb" at
5420 http://libpng.git.sourceforge.net/git/gitweb.cgi?p=libpng
5422 Patches can be sent to glennrp at users.sourceforge.net or to
5423 png-mng-implement at lists.sourceforge.net or you can upload them to
5424 the libpng bug tracker at
5426 http://libpng.sourceforge.net
5428 We also accept patches built from the tar or zip distributions, and
5429 simple verbal discriptions of bug fixes, reported either to the
5430 SourceForge bug tracker, to the png-mng-implement at lists.sf.net
5431 mailing list, or directly to glennrp.
5433 .SH XIII. Coding style
5435 Our coding style is similar to the "Allman" style, with curly
5436 braces on separate lines:
5443 else if (another condition)
5448 The braces can be omitted from simple one-line actions:
5453 We use 3-space indentation, except for continued statements which
5454 are usually indented the same as the first line of the statement
5455 plus four more spaces.
5457 For macro definitions we use 2-space indentation, always leaving the "#"
5458 in the first column.
5460 #ifndef PNG_NO_FEATURE
5461 # ifndef PNG_FEATURE_SUPPORTED
5462 # define PNG_FEATURE_SUPPORTED
5466 Comments appear with the leading "/*" at the same indentation as
5467 the statement that follows the comment:
5469 /* Single-line comment */
5472 /* This is a multiple-line
5477 Very short comments can be placed after the end of the statement
5478 to which they pertain:
5480 statement; /* comment */
5482 We don't use C++ style ("//") comments. We have, however,
5483 used them in the past in some now-abandoned MMX assembler
5486 Functions and their curly braces are not indented, and
5487 exported functions are marked with PNGAPI:
5489 /* This is a public function that is visible to
5490 * application programmers. It does thus-and-so.
5493 png_exported_function(png_ptr, png_info, foo)
5498 The prototypes for all exported functions appear in png.h,
5499 above the comment that says
5501 /* Maintainer: Put new public prototypes here ... */
5503 We mark all non-exported functions with "/* PRIVATE */"":
5506 png_non_exported_function(png_ptr, png_info, foo)
5511 The prototypes for non-exported functions (except for those in
5514 above the comment that says
5516 /* Maintainer: Put new private prototypes here ^ and in libpngpf.3 */
5518 To avoid polluting the global namespace, the names of all exported
5519 functions and variables begin with "png_", and all publicly visible C
5520 preprocessor macros begin with "PNG_". We request that applications that
5521 use libpng *not* begin any of their own symbols with either of these strings.
5523 We put a space after each comma and after each semicolon
5524 in "for" statements, and we put spaces before and after each
5525 C binary operator and after "for" or "while", and before
5526 "?". We don't put a space between a typecast and the expression
5527 being cast, nor do we put one between a function name and the
5528 left parenthesis that follows it:
5530 for (i = 2; i > 0; --i)
5531 y[i] = a(x) + (int)b;
5533 We prefer #ifdef and #ifndef to #if defined() and if !defined()
5534 when there is only one macro being tested.
5536 We prefer to express integers that are used as bit masks in hex format,
5537 with an even number of lower-case hex digits (e.g., 0x00, 0xff, 0x0100).
5539 We do not use the TAB character for indentation in the C sources.
5541 Lines do not exceed 80 characters.
5543 Other rules can be inferred by inspecting the libpng source.
5545 .SH XIV. Y2K Compliance in libpng
5549 Since the PNG Development group is an ad-hoc body, we can't make
5550 an official declaration.
5552 This is your unofficial assurance that libpng from version 0.71 and
5553 upward through 1.5.6 are Y2K compliant. It is my belief that earlier
5554 versions were also Y2K compliant.
5556 Libpng only has three year fields. One is a 2-byte unsigned integer that
5557 will hold years up to 65535. The other two hold the date in text
5558 format, and will hold years up to 9999.
5561 "png_uint_16 year" in png_time_struct.
5564 "png_charp time_buffer" in png_struct and
5565 "near_time_buffer", which is a local character string in png.c.
5567 There are seven time-related functions:
5569 png_convert_to_rfc_1123() in png.c
5570 (formerly png_convert_to_rfc_1152() in error)
5571 png_convert_from_struct_tm() in pngwrite.c, called
5573 png_convert_from_time_t() in pngwrite.c
5574 png_get_tIME() in pngget.c
5575 png_handle_tIME() in pngrutil.c, called in pngread.c
5576 png_set_tIME() in pngset.c
5577 png_write_tIME() in pngwutil.c, called in pngwrite.c
5579 All appear to handle dates properly in a Y2K environment. The
5580 png_convert_from_time_t() function calls gmtime() to convert from system
5581 clock time, which returns (year - 1900), which we properly convert to
5582 the full 4-digit year. There is a possibility that applications using
5583 libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
5584 function, or that they are incorrectly passing only a 2-digit year
5585 instead of "year - 1900" into the png_convert_from_struct_tm() function,
5586 but this is not under our control. The libpng documentation has always
5587 stated that it works with 4-digit years, and the APIs have been
5590 The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
5591 integer to hold the year, and can hold years as large as 65535.
5593 zlib, upon which libpng depends, is also Y2K compliant. It contains
5594 no date-related code.
5597 Glenn Randers-Pehrson
5599 PNG Development Group
5603 Note about libpng version numbers:
5605 Due to various miscommunications, unforeseen code incompatibilities
5606 and occasional factors outside the authors' control, version numbering
5607 on the library has not always been consistent and straightforward.
5608 The following table summarizes matters since version 0.89c, which was
5609 the first widely used release:
5611 source png.h png.h shared-lib
5612 version string int version
5613 ------- ------ ----- ----------
5614 0.89c ("beta 3") 0.89 89 1.0.89
5615 0.90 ("beta 4") 0.90 90 0.90
5616 0.95 ("beta 5") 0.95 95 0.95
5617 0.96 ("beta 6") 0.96 96 0.96
5618 0.97b ("beta 7") 1.00.97 97 1.0.1
5619 0.97c 0.97 97 2.0.97
5622 0.99a-m 0.99 99 2.0.99
5624 1.0.0 1.0.0 100 2.1.0
5625 1.0.0 (from here on, the 100 2.1.0
5626 1.0.1 png.h string is 10001 2.1.0
5627 1.0.1a-e identical to the 10002 from here on, the
5628 1.0.2 source version) 10002 shared library is 2.V
5629 1.0.2a-b 10003 where V is the source
5630 1.0.1 10001 code version except as
5631 1.0.1a-e 10002 2.1.0.1a-e noted.
5633 1.0.2a-b 10003 2.1.0.2a-b
5635 1.0.3a-d 10004 2.1.0.3a-d
5637 1.0.4a-f 10005 2.1.0.4a-f
5638 1.0.5 (+ 2 patches) 10005 2.1.0.5
5639 1.0.5a-d 10006 2.1.0.5a-d
5640 1.0.5e-r 10100 2.1.0.5e-r
5641 1.0.5s-v 10006 2.1.0.5s-v
5642 1.0.6 (+ 3 patches) 10006 2.1.0.6
5643 1.0.6d-g 10007 2.1.0.6d-g
5646 1.0.6j 10007 2.1.0.6j
5647 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
5648 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
5649 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
5650 1.0.7 1 10007 2.1.0.7
5651 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
5652 1.0.8rc1 1 10008 2.1.0.8rc1
5653 1.0.8 1 10008 2.1.0.8
5654 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
5655 1.0.9rc1 1 10009 2.1.0.9rc1
5656 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
5657 1.0.9rc2 1 10009 2.1.0.9rc2
5658 1.0.9 1 10009 2.1.0.9
5659 1.0.10beta1 1 10010 2.1.0.10beta1
5660 1.0.10rc1 1 10010 2.1.0.10rc1
5661 1.0.10 1 10010 2.1.0.10
5662 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
5663 1.0.11rc1 1 10011 2.1.0.11rc1
5664 1.0.11 1 10011 2.1.0.11
5665 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
5666 1.0.12rc1 2 10012 2.1.0.12rc1
5667 1.0.12 2 10012 2.1.0.12
5668 1.1.0a-f - 10100 2.1.1.0a-f abandoned
5669 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
5670 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
5671 1.2.0rc1 3 10200 3.1.2.0rc1
5672 1.2.0 3 10200 3.1.2.0
5673 1.2.1beta-4 3 10201 3.1.2.1beta1-4
5674 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
5675 1.2.1 3 10201 3.1.2.1
5676 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
5677 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
5678 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
5679 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
5680 1.0.13 10 10013 10.so.0.1.0.13
5681 1.2.2 12 10202 12.so.0.1.2.2
5682 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
5683 1.2.3 12 10203 12.so.0.1.2.3
5684 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
5685 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
5686 1.0.14 10 10014 10.so.0.1.0.14
5687 1.2.4 13 10204 12.so.0.1.2.4
5688 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
5689 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
5690 1.0.15 10 10015 10.so.0.1.0.15
5691 1.2.5 13 10205 12.so.0.1.2.5
5692 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
5693 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
5694 1.0.16 10 10016 10.so.0.1.0.16
5695 1.2.6 13 10206 12.so.0.1.2.6
5696 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
5697 1.0.17rc1 10 10017 12.so.0.1.0.17rc1
5698 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
5699 1.0.17 10 10017 12.so.0.1.0.17
5700 1.2.7 13 10207 12.so.0.1.2.7
5701 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
5702 1.0.18rc1-5 10 10018 12.so.0.1.0.18rc1-5
5703 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
5704 1.0.18 10 10018 12.so.0.1.0.18
5705 1.2.8 13 10208 12.so.0.1.2.8
5706 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3
5707 1.2.9beta4-11 13 10209 12.so.0.9[.0]
5708 1.2.9rc1 13 10209 12.so.0.9[.0]
5709 1.2.9 13 10209 12.so.0.9[.0]
5710 1.2.10beta1-7 13 10210 12.so.0.10[.0]
5711 1.2.10rc1-2 13 10210 12.so.0.10[.0]
5712 1.2.10 13 10210 12.so.0.10[.0]
5713 1.4.0beta1-6 14 10400 14.so.0.0[.0]
5714 1.2.11beta1-4 13 10210 12.so.0.11[.0]
5715 1.4.0beta7-8 14 10400 14.so.0.0[.0]
5716 1.2.11 13 10211 12.so.0.11[.0]
5717 1.2.12 13 10212 12.so.0.12[.0]
5718 1.4.0beta9-14 14 10400 14.so.0.0[.0]
5719 1.2.13 13 10213 12.so.0.13[.0]
5720 1.4.0beta15-36 14 10400 14.so.0.0[.0]
5721 1.4.0beta37-87 14 10400 14.so.14.0[.0]
5722 1.4.0rc01 14 10400 14.so.14.0[.0]
5723 1.4.0beta88-109 14 10400 14.so.14.0[.0]
5724 1.4.0rc02-08 14 10400 14.so.14.0[.0]
5725 1.4.0 14 10400 14.so.14.0[.0]
5726 1.4.1beta01-03 14 10401 14.so.14.1[.0]
5727 1.4.1rc01 14 10401 14.so.14.1[.0]
5728 1.4.1beta04-12 14 10401 14.so.14.1[.0]
5729 1.4.1 14 10401 14.so.14.1[.0]
5730 1.4.2 14 10402 14.so.14.2[.0]
5731 1.4.3 14 10403 14.so.14.3[.0]
5732 1.4.4 14 10404 14.so.14.4[.0]
5733 1.5.0beta01-58 15 10500 15.so.15.0[.0]
5734 1.5.0rc01-07 15 10500 15.so.15.0[.0]
5735 1.5.0 15 10500 15.so.15.0[.0]
5736 1.5.1beta01-11 15 10501 15.so.15.1[.0]
5737 1.5.1rc01-02 15 10501 15.so.15.1[.0]
5738 1.5.1 15 10501 15.so.15.1[.0]
5739 1.5.2beta01-03 15 10502 15.so.15.2[.0]
5740 1.5.2rc01-03 15 10502 15.so.15.2[.0]
5741 1.5.2 15 10502 15.so.15.2[.0]
5742 1.5.3beta01-10 15 10503 15.so.15.3[.0]
5743 1.5.3rc01-02 15 10503 15.so.15.3[.0]
5744 1.5.3beta11 15 10503 15.so.15.3[.0]
5746 1.5.4beta01-08 15 10504 15.so.15.4[.0]
5747 1.5.4rc01 15 10504 15.so.15.4[.0]
5748 1.5.4 15 10504 15.so.15.4[.0]
5749 1.5.5beta01-08 15 10505 15.so.15.5[.0]
5750 1.5.5rc01 15 10505 15.so.15.5[.0]
5751 1.5.5 15 10505 15.so.15.5[.0]
5752 1.5.6beta01-07 15 10506 15.so.15.6[.0]
5753 1.5.6rc01-03 15 10506 15.so.15.6[.0]
5754 1.5.6 15 10506 15.so.15.6[.0]
5756 Henceforth the source version will match the shared-library minor
5757 and patch numbers; the shared-library major version number will be
5758 used for changes in backward compatibility, as it is intended. The
5759 PNG_PNGLIB_VER macro, which is not used within libpng but is available
5760 for applications, is an unsigned integer of the form xyyzz corresponding
5761 to the source version x.y.z (leading zeros in y and z). Beta versions
5762 were given the previous public release number plus a letter, until
5763 version 1.0.6j; from then on they were given the upcoming public
5764 release number plus "betaNN" or "rcN".
5767 .BR "png"(5), " libpngpf"(3), " zlib"(3), " deflate"(5), " " and " zlib"(5)
5772 http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
5773 http://www.libpng.org/pub/png
5778 (generally) at the same location as
5782 ftp://ftp.info-zip.org/pub/infozip/zlib
5785 .IR PNG specification: RFC 2083
5787 (generally) at the same location as
5791 ftp://ds.internic.net/rfc/rfc2083.txt
5793 or (as a W3C Recommendation) at
5795 http://www.w3.org/TR/REC-png.html
5798 In the case of any inconsistency between the PNG specification
5799 and this library, the specification takes precedence.
5802 This man page: Glenn Randers-Pehrson
5803 <glennrp at users.sourceforge.net>
5805 The contributing authors would like to thank all those who helped
5806 with testing, bug fixes, and patience. This wouldn't have been
5807 possible without all of you.
5809 Thanks to Frank J. T. Wojcik for helping with the documentation.
5811 Libpng version 1.5.6 - November 3, 2011:
5812 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
5813 Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
5815 Supported by the PNG development group
5817 png-mng-implement at lists.sf.net
5818 (subscription required; visit
5819 png-mng-implement at lists.sourceforge.net (subscription required; visit
5820 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
5823 .SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
5825 (This copy of the libpng notices is provided for your convenience. In case of
5826 any discrepancy between this copy and the notices in the file png.h that is
5827 included in the libpng distribution, the latter shall prevail.)
5829 If you modify libpng you may insert additional notices immediately following
5832 This code is released under the libpng license.
5834 libpng versions 1.2.6, August 15, 2004, through 1.5.6, November 3, 2011, are
5835 Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are
5836 distributed according to the same disclaimer and license as libpng-1.2.5
5837 with the following individual added to the list of Contributing Authors
5841 libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
5842 Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
5843 distributed according to the same disclaimer and license as libpng-1.0.6
5844 with the following individuals added to the list of Contributing Authors
5846 Simon-Pierre Cadieux
5850 and with the following additions to the disclaimer:
5852 There is no warranty against interference with your
5853 enjoyment of the library or against infringement.
5854 There is no warranty that our efforts or the library
5855 will fulfill any of your particular purposes or needs.
5856 This library is provided with all faults, and the entire
5857 risk of satisfactory quality, performance, accuracy, and
5858 effort is with the user.
5860 libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
5861 Copyright (c) 1998, 1999 Glenn Randers-Pehrson
5862 Distributed according to the same disclaimer and license as libpng-0.96,
5863 with the following individuals added to the list of Contributing Authors:
5866 Glenn Randers-Pehrson
5869 libpng versions 0.89, June 1996, through 0.96, May 1997, are
5870 Copyright (c) 1996, 1997 Andreas Dilger
5871 Distributed according to the same disclaimer and license as libpng-0.88,
5872 with the following individuals added to the list of Contributing Authors:
5881 libpng versions 0.5, May 1995, through 0.88, January 1996, are
5882 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
5884 For the purposes of this copyright and license, "Contributing Authors"
5885 is defined as the following set of individuals:
5893 The PNG Reference Library is supplied "AS IS". The Contributing Authors
5894 and Group 42, Inc. disclaim all warranties, expressed or implied,
5895 including, without limitation, the warranties of merchantability and of
5896 fitness for any purpose. The Contributing Authors and Group 42, Inc.
5897 assume no liability for direct, indirect, incidental, special, exemplary,
5898 or consequential damages, which may result from the use of the PNG
5899 Reference Library, even if advised of the possibility of such damage.
5901 Permission is hereby granted to use, copy, modify, and distribute this
5902 source code, or portions hereof, for any purpose, without fee, subject
5903 to the following restrictions:
5905 1. The origin of this source code must not be misrepresented.
5907 2. Altered versions must be plainly marked as such and
5908 must not be misrepresented as being the original source.
5910 3. This Copyright notice may not be removed or altered from
5911 any source or altered source distribution.
5913 The Contributing Authors and Group 42, Inc. specifically permit, without
5914 fee, and encourage the use of this source code as a component to
5915 supporting the PNG file format in commercial products. If you use this
5916 source code in a product, acknowledgment is not required but would be
5920 A "png_get_copyright" function is available, for convenient use in "about"
5923 printf("%s",png_get_copyright(NULL));
5925 Also, the PNG logo (in PNG format, of course) is supplied in the
5926 files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
5928 Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
5929 certification mark of the Open Source Initiative.
5931 Glenn Randers-Pehrson
5932 glennrp at users.sourceforge.net
projects / wxWidgets.git / blob