1 .TH LIBPNG 3 "December 3, 2004"
3 libpng \- Portable Network Graphics (PNG) Reference Library 1.2.8
11 \fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
15 \fBint png_check_sig (png_bytep \fP\fIsig\fP\fB, int \fInum\fP\fB);\fP
19 \fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
23 \fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
27 \fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
31 \fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
35 \fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
39 \fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
43 \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
47 \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
51 \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
55 \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
59 \fBint png_debug(int \fP\fIlevel\fP\fB, png_const_charp \fImessage\fP\fB);\fP
63 \fBint png_debug1(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fIp1\fP\fB);\fP
67 \fBint png_debug2(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fP\fIp1\fP\fB, \fIp2\fP\fB);\fP
71 \fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
75 \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
79 \fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
83 \fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
87 \fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
91 \fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
95 \fBvoid png_free_default(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
99 \fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
103 \fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
107 \fBpng_uint_32 png_get_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
111 \fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
115 \fBpng_uint_32 png_get_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*white_x\fP\fB, double \fP\fI*white_y\fP\fB, double \fP\fI*red_x\fP\fB, double \fP\fI*red_y\fP\fB, double \fP\fI*green_x\fP\fB, double \fP\fI*green_y\fP\fB, double \fP\fI*blue_x\fP\fB, double \fI*blue_y\fP\fB);\fP
119 \fBpng_uint_32 png_get_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*white_x\fP\fB, png_uint_32 \fP\fI*white_y\fP\fB, png_uint_32 \fP\fI*red_x\fP\fB, png_uint_32 \fP\fI*red_y\fP\fB, png_uint_32 \fP\fI*green_x\fP\fB, png_uint_32 \fP\fI*green_y\fP\fB, png_uint_32 \fP\fI*blue_x\fP\fB, png_uint_32 \fI*blue_y\fP\fB);\fP
123 \fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
127 \fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
131 \fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
135 \fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
139 \fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
143 \fBpng_uint_32 png_get_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
147 \fBpng_uint_32 png_get_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
151 \fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
155 \fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
159 \fBpng_uint_32 png_get_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
163 \fBpng_uint_32 png_get_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_charpp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
167 \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
171 \fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
175 \fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
179 \fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
183 \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
187 \fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
191 \fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
195 \fBpng_uint_32 png_get_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*offset_x\fP\fB, png_uint_32 \fP\fI*offset_y\fP\fB, int \fI*unit_type\fP\fB);\fP
199 \fBpng_uint_32 png_get_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fI*purpose\fP\fB, png_int_32 \fP\fI*X0\fP\fB, png_int_32 \fP\fI*X1\fP\fB, int \fP\fI*type\fP\fB, int \fP\fI*nparams\fP\fB, png_charp \fP\fI*units\fP\fB, png_charpp \fI*params\fP\fB);\fP
203 \fBpng_uint_32 png_get_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
207 \fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
211 \fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
215 \fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
219 \fBpng_uint_32 png_get_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
223 \fBpng_byte png_get_rgb_to_gray_status (png_structp \fIpng_ptr)
225 \fBpng_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
229 \fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
233 \fBpng_uint_32 png_get_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
237 \fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
241 \fBpng_uint_32 png_get_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
245 \fBpng_uint_32 png_get_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fI*intent\fP\fB);\fP
249 \fBpng_uint_32 png_get_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
253 \fBpng_uint_32 png_get_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
257 \fBpng_uint_32 png_get_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_values\fP\fB);\fP
261 \fBpng_uint_32 png_get_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
265 \fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
269 \fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP
273 \fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
277 \fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP
281 \fBpng_uint_32 png_get_valid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
285 \fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
289 \fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
293 \fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
297 \fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
301 \fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
305 \fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
309 \fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
313 \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
317 \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
321 \fBDEPRECATED: void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP
325 \fBDEPRECATED: void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
329 \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
333 \fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
337 \fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
341 \fBpng_voidp png_memcpy_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
345 \fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
349 \fBpng_voidp png_memset_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
353 \fBDEPRECATED: void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_permitted\fP\fB);\fP
357 \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
361 \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
365 \fBvoid png_read_destroy (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_infop \fIend_info_ptr\fP\fB);\fP
369 \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
373 \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
377 \fBDEPRECATED: void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP
381 \fBDEPRECATED: void png_read_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
385 \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
389 \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
393 \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
397 \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
401 \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
405 \fB#if \fI!defined(PNG_1_0_X)
407 \fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
413 \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
417 \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
421 \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
425 \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
429 \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
433 \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
437 \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
441 \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
445 \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
449 \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
453 \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
457 \fBvoid png_set_dither (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_dither\fP\fB);\fP
461 \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
465 \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
469 \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
473 \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
477 \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
481 \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
485 \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
489 \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
493 \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
497 \fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
501 \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
505 \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
509 \fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_charp \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
513 \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
517 \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
521 \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
525 \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
529 \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
533 \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
537 \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
541 \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
545 \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
549 \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
553 \fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
557 \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
561 \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
565 \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
569 \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
573 \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
577 \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
581 \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
585 \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
589 \fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_fixed_point \fP\fIred\fP\fB, png_fixed_point \fIgreen\fP\fB);\fP
593 \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
597 \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
601 \fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
605 \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
609 \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
613 \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
617 \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
621 \fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
625 \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
629 \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
633 \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
637 \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
641 \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
645 \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
649 \fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_values\fP\fB);\fP
653 \fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
657 \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
661 \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
665 \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
669 \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
673 \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
677 \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
681 \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
685 \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
689 \fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
693 \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
697 \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
701 \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
705 \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
709 \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
713 \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
717 \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
721 \fBvoid png_write_destroy (png_structp \fIpng_ptr\fP\fB);\fP
725 \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
729 \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
733 \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
737 \fBDEPRECATED: void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP
741 \fBDEPRECATED: void png_write_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
745 \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
749 \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
753 \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
757 \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
761 \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
765 \fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
769 \fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
776 library supports encoding, decoding, and various manipulations of
777 the Portable Network Graphics (PNG) format image files. It uses the
780 Following is a copy of the libpng.txt file that accompanies libpng.
782 libpng.txt - A description on how to use and modify libpng
784 libpng version 1.2.8 - December 3, 2004
785 Updated and distributed by Glenn Randers-Pehrson
786 <glennrp at users.sourceforge.net>
787 Copyright (c) 1998-2004 Glenn Randers-Pehrson
788 For conditions of distribution and use, see copyright
793 libpng 1.0 beta 6 version 0.96 May 28, 1997
794 Updated and distributed by Andreas Dilger
795 Copyright (c) 1996, 1997 Andreas Dilger
797 libpng 1.0 beta 2 - version 0.88 January 26, 1996
798 For conditions of distribution and use, see copyright
799 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
800 Schalnat, Group 42, Inc.
802 Updated/rewritten per request in the libpng FAQ
803 Copyright (c) 1995, 1996 Frank J. T. Wojcik
804 December 18, 1995 & January 20, 1996
808 This file describes how to use and modify the PNG reference library
809 (known as libpng) for your own use. There are five sections to this
810 file: introduction, structures, reading, writing, and modification and
811 configuration notes for various special platforms. In addition to this
812 file, example.c is a good starting point for using the library, as
813 it is heavily commented and should include everything most people
814 will need. We assume that libpng is already installed; see the
815 INSTALL file for instructions on how to install libpng.
817 Libpng was written as a companion to the PNG specification, as a way
818 of reducing the amount of time and effort it takes to support the PNG
819 file format in application programs.
821 The PNG specification (second edition), November 2003, is available as
822 a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
823 <http://www.w3.org/TR/2003/REC-PNG-20031110/
824 The W3C and ISO documents have identical technical content.
826 The PNG-1.2 specification is available at
827 <http://www.libpng.org/pub/png/documents/>
829 The PNG-1.0 specification is available
830 as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
831 W3C Recommendation <http://www.w3.org/TR/REC.png.html>. Some
832 additional chunks are described in the special-purpose public chunks
833 documents at <http://www.libpng.org/pub/png/documents/>.
836 about PNG, and the latest version of libpng, can be found at the PNG home
837 page, <http://www.libpng.org/pub/png/>.
839 Most users will not have to modify the library significantly; advanced
840 users may want to modify it more. All attempts were made to make it as
841 complete as possible, while keeping the code easy to understand.
842 Currently, this library only supports C. Support for other languages
845 Libpng has been designed to handle multiple sessions at one time,
846 to be easily modifiable, to be portable to the vast majority of
847 machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
848 to use. The ultimate goal of libpng is to promote the acceptance of
849 the PNG file format in whatever way possible. While there is still
850 work to be done (see the TODO file), libpng should cover the
851 majority of the needs of its users.
853 Libpng uses zlib for its compression and decompression of PNG files.
854 Further information about zlib, and the latest version of zlib, can
855 be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
856 The zlib compression utility is a general purpose utility that is
857 useful for more than PNG files, and can be used without libpng.
858 See the documentation delivered with zlib for more details.
859 You can usually find the source files for the zlib utility wherever you
860 find the libpng source files.
862 Libpng is thread safe, provided the threads are using different
863 instances of the structures. Each thread should have its own
864 png_struct and png_info instances, and thus its own image.
865 Libpng does not protect itself against two threads using the
866 same instance of a structure. Note: thread safety may be defeated
867 by use of some of the MMX assembler code in pnggccrd.c, which is only
868 compiled when the user defines PNG_THREAD_UNSAFE_OK.
872 There are two main structures that are important to libpng, png_struct
873 and png_info. The first, png_struct, is an internal structure that
874 will not, for the most part, be used by a user except as the first
875 variable passed to every libpng function call.
877 The png_info structure is designed to provide information about the
878 PNG file. At one time, the fields of png_info were intended to be
879 directly accessible to the user. However, this tended to cause problems
880 with applications using dynamically loaded libraries, and as a result
881 a set of interface functions for png_info (the png_get_*() and png_set_*()
882 functions) was developed. The fields of png_info are still available for
883 older applications, but it is suggested that applications use the new
884 interfaces if at all possible.
886 Applications that do make direct access to the members of png_struct (except
887 for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
888 and applications that make direct access to the members of png_info must
889 be recompiled if they were compiled or loaded with libpng version 1.0.6,
890 in which the members were in a different order. In version 1.0.7, the
891 members of the png_info structure reverted to the old order, as they were
892 in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
893 structures are going to be hidden, and the contents of the structures will
894 only be accessible through the png_get/png_set functions.
896 The png.h header file is an invaluable reference for programming with libpng.
897 And while I'm on the topic, make sure you include the libpng header file:
903 We'll now walk you through the possible functions to call when reading
904 in a PNG file sequentially, briefly explaining the syntax and purpose
905 of each one. See example.c and png.h for more detail. While
906 progressive reading is covered in the next section, you will still
907 need some of the functions discussed in this section to read a PNG
912 You will want to do the I/O initialization(*) before you get into libpng,
913 so if it doesn't work, you don't have much to undo. Of course, you
914 will also want to insure that you are, in fact, dealing with a PNG
915 file. Libpng provides a simple check to see if a file is a PNG file.
916 To use it, pass in the first 1 to 8 bytes of the file to the function
917 png_sig_cmp(), and it will return 0 if the bytes match the corresponding
918 bytes of the PNG signature, or nonzero otherwise. Of course, the more bytes
919 you pass in, the greater the accuracy of the prediction.
921 If you are intending to keep the file pointer open for use in libpng,
922 you must ensure you don't read more than 8 bytes from the beginning
923 of the file, and you also have to make a call to png_set_sig_bytes_read()
924 with the number of bytes you read from the beginning. Libpng will
925 then only check the bytes (if any) that your program didn't read.
927 (*): If you are not using the standard I/O functions, you will need
928 to replace them with custom functions. See the discussion under
932 FILE *fp = fopen(file_name, "rb");
937 fread(header, 1, number, fp);
938 is_png = !png_sig_cmp(header, 0, number);
945 Next, png_struct and png_info need to be allocated and initialized. In
946 order to ensure that the size of these structures is correct even with a
947 dynamically linked libpng, there are functions to initialize and
948 allocate the structures. We also pass the library version, optional
949 pointers to error handling functions, and a pointer to a data struct for
950 use by the error functions, if necessary (the pointer and functions can
951 be NULL if the default error handlers are to be used). See the section
952 on Changes to Libpng below regarding the old initialization functions.
953 The structure allocation functions quietly return NULL if they fail to
954 create the structure, so your application should check for that.
956 png_structp png_ptr = png_create_read_struct
957 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
958 user_error_fn, user_warning_fn);
962 png_infop info_ptr = png_create_info_struct(png_ptr);
965 png_destroy_read_struct(&png_ptr,
966 (png_infopp)NULL, (png_infopp)NULL);
970 png_infop end_info = png_create_info_struct(png_ptr);
973 png_destroy_read_struct(&png_ptr, &info_ptr,
978 If you want to use your own memory allocation routines,
979 define PNG_USER_MEM_SUPPORTED and use
980 png_create_read_struct_2() instead of png_create_read_struct():
982 png_structp png_ptr = png_create_read_struct_2
983 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
984 user_error_fn, user_warning_fn, (png_voidp)
985 user_mem_ptr, user_malloc_fn, user_free_fn);
987 The error handling routines passed to png_create_read_struct()
988 and the memory alloc/free routines passed to png_create_struct_2()
989 are only necessary if you are not using the libpng supplied error
990 handling and memory alloc/free functions.
992 When libpng encounters an error, it expects to longjmp back
993 to your routine. Therefore, you will need to call setjmp and pass
994 your png_jmpbuf(png_ptr). If you read the file from different
995 routines, you will need to update the jmpbuf field every time you enter
996 a new routine that will call a png_*() function.
998 See your documentation of setjmp/longjmp for your compiler for more
999 information on setjmp/longjmp. See the discussion on libpng error
1000 handling in the Customizing Libpng section below for more information
1001 on the libpng error handling. If an error occurs, and libpng longjmp's
1002 back to your setjmp, you will want to call png_destroy_read_struct() to
1005 if (setjmp(png_jmpbuf(png_ptr)))
1007 png_destroy_read_struct(&png_ptr, &info_ptr,
1013 If you would rather avoid the complexity of setjmp/longjmp issues,
1014 you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
1015 errors will result in a call to PNG_ABORT() which defaults to abort().
1017 Now you need to set up the input code. The default for libpng is to
1018 use the C function fread(). If you use this, you will need to pass a
1019 valid FILE * in the function png_init_io(). Be sure that the file is
1020 opened in binary mode. If you wish to handle reading data in another
1021 way, you need not call the png_init_io() function, but you must then
1022 implement the libpng I/O methods discussed in the Customizing Libpng
1025 png_init_io(png_ptr, fp);
1027 If you had previously opened the file and read any of the signature from
1028 the beginning in order to see if this was a PNG file, you need to let
1029 libpng know that there are some bytes missing from the start of the file.
1031 png_set_sig_bytes(png_ptr, number);
1033 .SS Setting up callback code
1035 You can set up a callback function to handle any unknown chunks in the
1036 input stream. You must supply the function
1038 read_chunk_callback(png_ptr ptr,
1039 png_unknown_chunkp chunk);
1041 /* The unknown chunk structure contains your
1046 /* Note that libpng has already taken care of
1049 /* put your code here. Return one of the
1052 return (-n); /* chunk had an error */
1053 return (0); /* did not recognize */
1054 return (n); /* success */
1057 (You can give your function another name that you like instead of
1058 "read_chunk_callback")
1060 To inform libpng about your function, use
1062 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1063 read_chunk_callback);
1065 This names not only the callback function, but also a user pointer that
1066 you can retrieve with
1068 png_get_user_chunk_ptr(png_ptr);
1070 At this point, you can set up a callback function that will be
1071 called after each row has been read, which you can use to control
1072 a progress meter or the like. It's demonstrated in pngtest.c.
1073 You must supply a function
1075 void read_row_callback(png_ptr ptr, png_uint_32 row,
1078 /* put your code here */
1081 (You can give it another name that you like instead of "read_row_callback")
1083 To inform libpng about your function, use
1085 png_set_read_status_fn(png_ptr, read_row_callback);
1087 .SS Width and height limits
1089 The PNG specification allows the width and height of an image to be as
1090 large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1091 Since very few applications really need to process such large images,
1092 we have imposed an arbitrary 1-million limit on rows and columns.
1093 Larger images will be rejected immediately with a png_error() call. If
1094 you wish to override this limit, you can use
1096 png_set_user_limits(png_ptr, width_max, height_max);
1098 to set your own limits, or use width_max = height_max = 0x7fffffffL
1099 to allow all valid dimensions (libpng may reject some very large images
1100 anyway because of potential buffer overflow conditions).
1102 You should put this statement after you create the PNG structure and
1103 before calling png_read_info(), png_read_png(), or png_process_data().
1104 If you need to retrieve the limits that are being applied, use
1106 width_max = png_get_user_width_max(png_ptr);
1107 height_max = png_get_user_height_max(png_ptr);
1109 .SS Unknown-chunk handling
1111 Now you get to set the way the library processes unknown chunks in the
1112 input PNG stream. Both known and unknown chunks will be read. Normal
1113 behavior is that known chunks will be parsed into information in
1114 various info_ptr members; unknown chunks will be discarded. To change
1117 png_set_keep_unknown_chunks(png_ptr, keep,
1118 chunk_list, num_chunks);
1119 keep - 0: do not handle as unknown
1121 2: keep only if safe-to-copy
1122 3: keep even if unsafe-to-copy
1123 You can use these definitions:
1124 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1125 PNG_HANDLE_CHUNK_NEVER 1
1126 PNG_HANDLE_CHUNK_IF_SAFE 2
1127 PNG_HANDLE_CHUNK_ALWAYS 3
1128 chunk_list - list of chunks affected (a byte string,
1129 five bytes per chunk, NULL or '\0' if
1131 num_chunks - number of chunks affected; if 0, all
1132 unknown chunks are affected. If nonzero,
1133 only the chunks in the list are affected
1135 Unknown chunks declared in this way will be saved as raw data onto a
1136 list of png_unknown_chunk structures. If a chunk that is normally
1137 known to libpng is named in the list, it will be handled as unknown,
1138 according to the "keep" directive. If a chunk is named in successive
1139 instances of png_set_keep_unknown_chunks(), the final instance will
1140 take precedence. The IHDR and IEND chunks should not be named in
1141 chunk_list; if they are, libpng will process them normally anyway.
1143 .SS The high-level read interface
1145 At this point there are two ways to proceed; through the high-level
1146 read interface, or through a sequence of low-level read operations.
1147 You can use the high-level interface if (a) you are willing to read
1148 the entire image into memory, and (b) the input transformations
1149 you want to do are limited to the following set:
1151 PNG_TRANSFORM_IDENTITY No transformation
1152 PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
1154 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1155 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1157 PNG_TRANSFORM_PACKSWAP Change order of packed
1159 PNG_TRANSFORM_EXPAND Perform set_expand()
1160 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1161 PNG_TRANSFORM_SHIFT Normalize pixels to the
1163 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1165 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1167 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1169 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1171 (This excludes setting a background color, doing gamma transformation,
1172 dithering, and setting filler.) If this is the case, simply do this:
1174 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1176 where png_transforms is an integer containing the logical OR of
1177 some set of transformation flags. This call is equivalent to png_read_info(),
1178 followed the set of transformations indicated by the transform mask,
1179 then png_read_image(), and finally png_read_end().
1181 (The final parameter of this call is not yet used. Someday it might point
1182 to transformation parameters required by some future input transform.)
1184 You must use png_transforms and not call any png_set_transform() functions
1185 when you use png_read_png().
1187 After you have called png_read_png(), you can retrieve the image data
1190 row_pointers = png_get_rows(png_ptr, info_ptr);
1192 where row_pointers is an array of pointers to the pixel data for each row:
1194 png_bytep row_pointers[height];
1196 If you know your image size and pixel size ahead of time, you can allocate
1197 row_pointers prior to calling png_read_png() with
1199 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1201 "Image is too tall to process in memory");
1202 if (width > PNG_UINT_32_MAX/pixel_size)
1204 "Image is too wide to process in memory");
1205 row_pointers = png_malloc(png_ptr,
1206 height*png_sizeof(png_bytep));
1207 for (int i=0; i<height, i++)
1208 row_pointers[i]=png_malloc(png_ptr,
1210 png_set_rows(png_ptr, info_ptr, &row_pointers);
1212 Alternatively you could allocate your image in one big block and define
1213 row_pointers[i] to point into the proper places in your block.
1215 If you use png_set_rows(), the application is responsible for freeing
1216 row_pointers (and row_pointers[i], if they were separately allocated).
1218 If you don't allocate row_pointers ahead of time, png_read_png() will
1219 do it, and it'll be free'ed when you call png_destroy_*().
1221 .SS The low-level read interface
1223 If you are going the low-level route, you are now ready to read all
1224 the file information up to the actual image data. You do this with a
1225 call to png_read_info().
1227 png_read_info(png_ptr, info_ptr);
1229 This will process all chunks up to but not including the image data.
1231 .SS Querying the info structure
1233 Functions are used to get the information from the info_ptr once it
1234 has been read. Note that these fields may not be completely filled
1235 in until png_read_end() has read the chunk data following the image.
1237 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1238 &bit_depth, &color_type, &interlace_type,
1239 &compression_type, &filter_method);
1241 width - holds the width of the image
1242 in pixels (up to 2^31).
1243 height - holds the height of the image
1244 in pixels (up to 2^31).
1245 bit_depth - holds the bit depth of one of the
1246 image channels. (valid values are
1247 1, 2, 4, 8, 16 and depend also on
1248 the color_type. See also
1249 significant bits (sBIT) below).
1250 color_type - describes which color/alpha channels
1253 (bit depths 1, 2, 4, 8, 16)
1254 PNG_COLOR_TYPE_GRAY_ALPHA
1256 PNG_COLOR_TYPE_PALETTE
1257 (bit depths 1, 2, 4, 8)
1260 PNG_COLOR_TYPE_RGB_ALPHA
1263 PNG_COLOR_MASK_PALETTE
1264 PNG_COLOR_MASK_COLOR
1265 PNG_COLOR_MASK_ALPHA
1267 filter_method - (must be PNG_FILTER_TYPE_BASE
1268 for PNG 1.0, and can also be
1269 PNG_INTRAPIXEL_DIFFERENCING if
1270 the PNG datastream is embedded in
1271 a MNG-1.0 datastream)
1272 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1274 interlace_type - (PNG_INTERLACE_NONE or
1275 PNG_INTERLACE_ADAM7)
1276 Any or all of interlace_type, compression_type, of
1277 filter_method can be NULL if you are
1278 not interested in their values.
1280 channels = png_get_channels(png_ptr, info_ptr);
1281 channels - number of channels of info for the
1282 color type (valid values are 1 (GRAY,
1283 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1284 4 (RGB_ALPHA or RGB + filler byte))
1285 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1286 rowbytes - number of bytes needed to hold a row
1288 signature = png_get_signature(png_ptr, info_ptr);
1289 signature - holds the signature read from the
1290 file (if any). The data is kept in
1291 the same offset it would be if the
1292 whole signature were read (i.e. if an
1293 application had already read in 4
1294 bytes of signature before starting
1295 libpng, the remaining 4 bytes would
1296 be in signature[4] through signature[7]
1297 (see png_set_sig_bytes())).
1300 width = png_get_image_width(png_ptr,
1302 height = png_get_image_height(png_ptr,
1304 bit_depth = png_get_bit_depth(png_ptr,
1306 color_type = png_get_color_type(png_ptr,
1308 filter_method = png_get_filter_type(png_ptr,
1310 compression_type = png_get_compression_type(png_ptr,
1312 interlace_type = png_get_interlace_type(png_ptr,
1316 These are also important, but their validity depends on whether the chunk
1317 has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1318 png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1319 data has been read, or zero if it is missing. The parameters to the
1320 png_get_<chunk> are set directly if they are simple data types, or a pointer
1321 into the info_ptr is returned for any complex types.
1323 png_get_PLTE(png_ptr, info_ptr, &palette,
1325 palette - the palette for the file
1326 (array of png_color)
1327 num_palette - number of entries in the palette
1329 png_get_gAMA(png_ptr, info_ptr, &gamma);
1330 gamma - the gamma the file is written
1333 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1334 srgb_intent - the rendering intent (PNG_INFO_sRGB)
1335 The presence of the sRGB chunk
1336 means that the pixel data is in the
1337 sRGB color space. This chunk also
1338 implies specific values of gAMA and
1341 png_get_iCCP(png_ptr, info_ptr, &name,
1342 &compression_type, &profile, &proflen);
1343 name - The profile name.
1344 compression - The compression type; always
1345 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1346 You may give NULL to this argument to
1348 profile - International Color Consortium color
1349 profile data. May contain NULs.
1350 proflen - length of profile data in bytes.
1352 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1353 sig_bit - the number of significant bits for
1354 (PNG_INFO_sBIT) each of the gray,
1355 red, green, and blue channels,
1356 whichever are appropriate for the
1357 given color type (png_color_16)
1359 png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
1361 trans - array of transparent entries for
1362 palette (PNG_INFO_tRNS)
1363 trans_values - graylevel or color sample values of
1364 the single transparent color for
1365 non-paletted images (PNG_INFO_tRNS)
1366 num_trans - number of transparent entries
1369 png_get_hIST(png_ptr, info_ptr, &hist);
1371 hist - histogram of palette (array of
1374 png_get_tIME(png_ptr, info_ptr, &mod_time);
1375 mod_time - time image was last modified
1378 png_get_bKGD(png_ptr, info_ptr, &background);
1379 background - background color (PNG_VALID_bKGD)
1380 valid 16-bit red, green and blue
1381 values, regardless of color_type
1383 num_comments = png_get_text(png_ptr, info_ptr,
1384 &text_ptr, &num_text);
1385 num_comments - number of comments
1386 text_ptr - array of png_text holding image
1388 text_ptr[i].compression - type of compression used
1389 on "text" PNG_TEXT_COMPRESSION_NONE
1390 PNG_TEXT_COMPRESSION_zTXt
1391 PNG_ITXT_COMPRESSION_NONE
1392 PNG_ITXT_COMPRESSION_zTXt
1393 text_ptr[i].key - keyword for comment. Must contain
1395 text_ptr[i].text - text comments for current
1396 keyword. Can be empty.
1397 text_ptr[i].text_length - length of text string,
1398 after decompression, 0 for iTXt
1399 text_ptr[i].itxt_length - length of itxt string,
1400 after decompression, 0 for tEXt/zTXt
1401 text_ptr[i].lang - language of comment (empty
1402 string for unknown).
1403 text_ptr[i].lang_key - keyword in UTF-8
1404 (empty string for unknown).
1405 num_text - number of comments (same as
1406 num_comments; you can put NULL here
1407 to avoid the duplication)
1408 Note while png_set_text() will accept text, language,
1409 and translated keywords that can be NULL pointers, the
1410 structure returned by png_get_text will always contain
1411 regular zero-terminated C strings. They might be
1412 empty strings but they will never be NULL pointers.
1414 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1416 palette_ptr - array of palette structures holding
1417 contents of one or more sPLT chunks
1419 num_spalettes - number of sPLT chunks read.
1421 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
1423 offset_x - positive offset from the left edge
1425 offset_y - positive offset from the top edge
1427 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1429 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
1431 res_x - pixels/unit physical resolution in
1433 res_y - pixels/unit physical resolution in
1435 unit_type - PNG_RESOLUTION_UNKNOWN,
1436 PNG_RESOLUTION_METER
1438 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1440 unit - physical scale units (an integer)
1441 width - width of a pixel in physical scale units
1442 height - height of a pixel in physical scale units
1443 (width and height are doubles)
1445 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1447 unit - physical scale units (an integer)
1448 width - width of a pixel in physical scale units
1449 height - height of a pixel in physical scale units
1450 (width and height are strings like "2.54")
1452 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1453 info_ptr, &unknowns)
1454 unknowns - array of png_unknown_chunk
1455 structures holding unknown chunks
1456 unknowns[i].name - name of unknown chunk
1457 unknowns[i].data - data of unknown chunk
1458 unknowns[i].size - size of unknown chunk's data
1459 unknowns[i].location - position of chunk in file
1461 The value of "i" corresponds to the order in which the
1462 chunks were read from the PNG file or inserted with the
1463 png_set_unknown_chunks() function.
1465 The data from the pHYs chunk can be retrieved in several convenient
1468 res_x = png_get_x_pixels_per_meter(png_ptr,
1470 res_y = png_get_y_pixels_per_meter(png_ptr,
1472 res_x_and_y = png_get_pixels_per_meter(png_ptr,
1474 res_x = png_get_x_pixels_per_inch(png_ptr,
1476 res_y = png_get_y_pixels_per_inch(png_ptr,
1478 res_x_and_y = png_get_pixels_per_inch(png_ptr,
1480 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
1483 (Each of these returns 0 [signifying "unknown"] if
1484 the data is not present or if res_x is 0;
1485 res_x_and_y is 0 if res_x != res_y)
1487 The data from the oFFs chunk can be retrieved in several convenient
1490 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
1491 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
1492 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
1493 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
1495 (Each of these returns 0 [signifying "unknown" if both
1496 x and y are 0] if the data is not present or if the
1497 chunk is present but the unit is the pixel)
1499 For more information, see the png_info definition in png.h and the
1500 PNG specification for chunk contents. Be careful with trusting
1501 rowbytes, as some of the transformations could increase the space
1502 needed to hold a row (expand, filler, gray_to_rgb, etc.).
1503 See png_read_update_info(), below.
1505 A quick word about text_ptr and num_text. PNG stores comments in
1506 keyword/text pairs, one pair per chunk, with no limit on the number
1507 of text chunks, and a 2^31 byte limit on their size. While there are
1508 suggested keywords, there is no requirement to restrict the use to these
1509 strings. It is strongly suggested that keywords and text be sensible
1510 to humans (that's the point), so don't use abbreviations. Non-printing
1511 symbols are not allowed. See the PNG specification for more details.
1512 There is also no requirement to have text after the keyword.
1514 Keywords should be limited to 79 Latin-1 characters without leading or
1515 trailing spaces, but non-consecutive spaces are allowed within the
1516 keyword. It is possible to have the same keyword any number of times.
1517 The text_ptr is an array of png_text structures, each holding a
1518 pointer to a language string, a pointer to a keyword and a pointer to
1519 a text string. The text string, language code, and translated
1520 keyword may be empty or NULL pointers. The keyword/text
1521 pairs are put into the array in the order that they are received.
1522 However, some or all of the text chunks may be after the image, so, to
1523 make sure you have read all the text chunks, don't mess with these
1524 until after you read the stuff after the image. This will be
1525 mentioned again below in the discussion that goes with png_read_end().
1527 .SS Input transformations
1529 After you've read the header information, you can set up the library
1530 to handle any special transformations of the image data. The various
1531 ways to transform the data will be described in the order that they
1532 should occur. This is important, as some of these change the color
1533 type and/or bit depth of the data, and some others only work on
1534 certain color types and bit depths. Even though each transformation
1535 checks to see if it has data that it can do something with, you should
1536 make sure to only enable a transformation if it will be valid for the
1537 data. For example, don't swap red and blue on grayscale data.
1539 The colors used for the background and transparency values should be
1540 supplied in the same format/depth as the current image data. They
1541 are stored in the same format/depth as the image data in a bKGD or tRNS
1542 chunk, so this is what libpng expects for this data. The colors are
1543 transformed to keep in sync with the image data when an application
1544 calls the png_read_update_info() routine (see below).
1546 Data will be decoded into the supplied row buffers packed into bytes
1547 unless the library has been told to transform it into another format.
1548 For example, 4 bit/pixel paletted or grayscale data will be returned
1549 2 pixels/byte with the leftmost pixel in the high-order bits of the
1550 byte, unless png_set_packing() is called. 8-bit RGB data will be stored
1551 in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
1552 is called to insert filler bytes, either before or after each RGB triplet.
1553 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
1554 byte of the color value first, unless png_set_strip_16() is called to
1555 transform it to regular RGB RGB triplets, or png_set_filler() or
1556 png_set_add alpha() is called to insert filler bytes, either before or
1557 after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
1559 png_set_filler(), png_set_add_alpha(), or png_set_strip_16().
1561 The following code transforms grayscale images of less than 8 to 8 bits,
1562 changes paletted images to RGB, and adds a full alpha channel if there is
1563 transparency information in a tRNS chunk. This is most useful on
1564 grayscale images with bit depths of 2 or 4 or if there is a multiple-image
1565 viewing application that wishes to treat all images in the same way.
1567 if (color_type == PNG_COLOR_TYPE_PALETTE)
1568 png_set_palette_to_rgb(png_ptr);
1570 if (color_type == PNG_COLOR_TYPE_GRAY &&
1571 bit_depth < 8) png_set_gray_1_2_4_to_8(png_ptr);
1573 if (png_get_valid(png_ptr, info_ptr,
1574 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
1576 These three functions are actually aliases for png_set_expand(), added
1577 in libpng version 1.0.4, with the function names expanded to improve code
1578 readability. In some future version they may actually do different
1581 PNG can have files with 16 bits per channel. If you only can handle
1582 8 bits per channel, this will strip the pixels down to 8 bit.
1584 if (bit_depth == 16)
1585 png_set_strip_16(png_ptr);
1587 If, for some reason, you don't need the alpha channel on an image,
1588 and you want to remove it rather than combining it with the background
1589 (but the image author certainly had in mind that you *would* combine
1590 it with the background, so that's what you should probably do):
1592 if (color_type & PNG_COLOR_MASK_ALPHA)
1593 png_set_strip_alpha(png_ptr);
1595 In PNG files, the alpha channel in an image
1596 is the level of opacity. If you need the alpha channel in an image to
1597 be the level of transparency instead of opacity, you can invert the
1598 alpha channel (or the tRNS chunk data) after it's read, so that 0 is
1599 fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
1600 images) is fully transparent, with
1602 png_set_invert_alpha(png_ptr);
1604 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
1605 they can, resulting in, for example, 8 pixels per byte for 1 bit
1606 files. This code expands to 1 pixel per byte without changing the
1607 values of the pixels:
1610 png_set_packing(png_ptr);
1612 PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
1613 stored in a PNG image have been "scaled" or "shifted" up to the next
1614 higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] to
1615 8 bits/sample in the range [0, 255]). However, it is also possible to
1616 convert the PNG pixel data back to the original bit depth of the image.
1617 This call reduces the pixels back down to the original bit depth:
1619 png_color_8p sig_bit;
1621 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
1622 png_set_shift(png_ptr, sig_bit);
1624 PNG files store 3-color pixels in red, green, blue order. This code
1625 changes the storage of the pixels to blue, green, red:
1627 if (color_type == PNG_COLOR_TYPE_RGB ||
1628 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1629 png_set_bgr(png_ptr);
1631 PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
1632 into 4 or 8 bytes for windowing systems that need them in this format:
1634 if (color_type == PNG_COLOR_TYPE_RGB)
1635 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
1637 where "filler" is the 8 or 16-bit number to fill with, and the location is
1638 either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
1639 you want the filler before the RGB or after. This transformation
1640 does not affect images that already have full alpha channels. To add an
1641 opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
1642 will generate RGBA pixels.
1644 Note that png_set_filler() does not change the color type. If you want
1645 to do that, you can add a true alpha channel with
1647 if (color_type == PNG_COLOR_TYPE_RGB ||
1648 color_type == PNG_COLOR_TYPE_GRAY)
1649 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
1651 where "filler" contains the alpha value to assign to each pixel.
1652 This function was added in libpng-1.2.7.
1654 If you are reading an image with an alpha channel, and you need the
1655 data as ARGB instead of the normal PNG format RGBA:
1657 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1658 png_set_swap_alpha(png_ptr);
1660 For some uses, you may want a grayscale image to be represented as
1661 RGB. This code will do that conversion:
1663 if (color_type == PNG_COLOR_TYPE_GRAY ||
1664 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1665 png_set_gray_to_rgb(png_ptr);
1667 Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
1670 if (color_type == PNG_COLOR_TYPE_RGB ||
1671 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1672 png_set_rgb_to_gray_fixed(png_ptr, error_action,
1673 int red_weight, int green_weight);
1675 error_action = 1: silently do the conversion
1676 error_action = 2: issue a warning if the original
1677 image has any pixel where
1678 red != green or red != blue
1679 error_action = 3: issue an error and abort the
1680 conversion if the original
1681 image has any pixel where
1682 red != green or red != blue
1684 red_weight: weight of red component times 100000
1685 green_weight: weight of green component times 100000
1686 If either weight is negative, default
1687 weights (21268, 71514) are used.
1689 If you have set error_action = 1 or 2, you can
1690 later check whether the image really was gray, after processing
1691 the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
1692 It will return a png_byte that is zero if the image was gray or
1693 1 if there were any non-gray pixels. bKGD and sBIT data
1694 will be silently converted to grayscale, using the green channel
1695 data, regardless of the error_action setting.
1697 With red_weight+green_weight<=100000,
1698 the normalized graylevel is computed:
1700 int rw = red_weight * 65536;
1701 int gw = green_weight * 65536;
1702 int bw = 65536 - (rw + gw);
1703 gray = (rw*red + gw*green + bw*blue)/65536;
1705 The default values approximate those recommended in the Charles
1706 Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
1707 Copyright (c) 1998-01-04 Charles Poynton <poynton at inforamp.net>
1709 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
1711 Libpng approximates this with
1713 Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
1715 which can be expressed with integers as
1717 Y = (6969 * R + 23434 * G + 2365 * B)/32768
1719 The calculation is done in a linear colorspace, if the image gamma
1722 If you have a grayscale and you are using png_set_expand_depth(),
1723 png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
1724 a higher bit-depth, you must either supply the background color as a gray
1725 value at the original file bit-depth (need_expand = 1) or else supply the
1726 background color as an RGB triplet at the final, expanded bit depth
1727 (need_expand = 0). Similarly, if you are reading a paletted image, you
1728 must either supply the background color as a palette index (need_expand = 1)
1729 or as an RGB triplet that may or may not be in the palette (need_expand = 0).
1731 png_color_16 my_background;
1732 png_color_16p image_background;
1734 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
1735 png_set_background(png_ptr, image_background,
1736 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
1738 png_set_background(png_ptr, &my_background,
1739 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
1741 The png_set_background() function tells libpng to composite images
1742 with alpha or simple transparency against the supplied background
1743 color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
1744 you may use this color, or supply another color more suitable for
1745 the current display (e.g., the background color from a web page). You
1746 need to tell libpng whether the color is in the gamma space of the
1747 display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
1748 (PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
1749 that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
1750 know why anyone would use this, but it's here).
1752 To properly display PNG images on any kind of system, the application needs
1753 to know what the display gamma is. Ideally, the user will know this, and
1754 the application will allow them to set it. One method of allowing the user
1755 to set the display gamma separately for each system is to check for a
1756 SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
1759 Note that display_gamma is the overall gamma correction required to produce
1760 pleasing results, which depends on the lighting conditions in the surrounding
1761 environment. In a dim or brightly lit room, no compensation other than
1762 the physical gamma exponent of the monitor is needed, while in a dark room
1763 a slightly smaller exponent is better.
1765 double gamma, screen_gamma;
1767 if (/* We have a user-defined screen
1770 screen_gamma = user_defined_screen_gamma;
1772 /* One way that applications can share the same
1773 screen gamma value */
1774 else if ((gamma_str = getenv("SCREEN_GAMMA"))
1777 screen_gamma = (double)atof(gamma_str);
1779 /* If we don't have another value */
1782 screen_gamma = 2.2; /* A good guess for a
1783 PC monitor in a bright office or a dim room */
1784 screen_gamma = 2.0; /* A good guess for a
1785 PC monitor in a dark room */
1786 screen_gamma = 1.7 or 1.0; /* A good
1787 guess for Mac systems */
1790 The png_set_gamma() function handles gamma transformations of the data.
1791 Pass both the file gamma and the current screen_gamma. If the file does
1792 not have a gamma value, you can pass one anyway if you have an idea what
1793 it is (usually 0.45455 is a good guess for GIF images on PCs). Note
1794 that file gammas are inverted from screen gammas. See the discussions
1795 on gamma in the PNG specification for an excellent description of what
1796 gamma is, and why all applications should support it. It is strongly
1797 recommended that PNG viewers support gamma correction.
1799 if (png_get_gAMA(png_ptr, info_ptr, &gamma))
1800 png_set_gamma(png_ptr, screen_gamma, gamma);
1802 png_set_gamma(png_ptr, screen_gamma, 0.45455);
1804 If you need to reduce an RGB file to a paletted file, or if a paletted
1805 file has more entries then will fit on your screen, png_set_dither()
1806 will do that. Note that this is a simple match dither that merely
1807 finds the closest color available. This should work fairly well with
1808 optimized palettes, and fairly badly with linear color cubes. If you
1809 pass a palette that is larger then maximum_colors, the file will
1810 reduce the number of colors in the palette so it will fit into
1811 maximum_colors. If there is a histogram, it will use it to make
1812 more intelligent choices when reducing the palette. If there is no
1813 histogram, it may not do as good a job.
1815 if (color_type & PNG_COLOR_MASK_COLOR)
1817 if (png_get_valid(png_ptr, info_ptr,
1820 png_uint_16p histogram = NULL;
1822 png_get_hIST(png_ptr, info_ptr,
1824 png_set_dither(png_ptr, palette, num_palette,
1825 max_screen_colors, histogram, 1);
1829 png_color std_color_cube[MAX_SCREEN_COLORS] =
1832 png_set_dither(png_ptr, std_color_cube,
1833 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
1838 PNG files describe monochrome as black being zero and white being one.
1839 The following code will reverse this (make black be one and white be
1842 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
1843 png_set_invert_mono(png_ptr);
1845 This function can also be used to invert grayscale and gray-alpha images:
1847 if (color_type == PNG_COLOR_TYPE_GRAY ||
1848 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1849 png_set_invert_mono(png_ptr);
1851 PNG files store 16 bit pixels in network byte order (big-endian,
1852 ie. most significant bits first). This code changes the storage to the
1853 other way (little-endian, i.e. least significant bits first, the
1854 way PCs store them):
1856 if (bit_depth == 16)
1857 png_set_swap(png_ptr);
1859 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
1860 need to change the order the pixels are packed into bytes, you can use:
1863 png_set_packswap(png_ptr);
1865 Finally, you can write your own transformation function if none of
1866 the existing ones meets your needs. This is done by setting a callback
1869 png_set_read_user_transform_fn(png_ptr,
1872 You must supply the function
1874 void read_transform_fn(png_ptr ptr, row_info_ptr
1875 row_info, png_bytep data)
1877 See pngtest.c for a working example. Your function will be called
1878 after all of the other transformations have been processed.
1880 You can also set up a pointer to a user structure for use by your
1881 callback function, and you can inform libpng that your transform
1882 function will change the number of channels or bit depth with the
1885 png_set_user_transform_info(png_ptr, user_ptr,
1886 user_depth, user_channels);
1888 The user's application, not libpng, is responsible for allocating and
1889 freeing any memory required for the user structure.
1891 You can retrieve the pointer via the function
1892 png_get_user_transform_ptr(). For example:
1894 voidp read_user_transform_ptr =
1895 png_get_user_transform_ptr(png_ptr);
1897 The last thing to handle is interlacing; this is covered in detail below,
1898 but you must call the function here if you want libpng to handle expansion
1899 of the interlaced image.
1901 number_of_passes = png_set_interlace_handling(png_ptr);
1903 After setting the transformations, libpng can update your png_info
1904 structure to reflect any transformations you've requested with this
1905 call. This is most useful to update the info structure's rowbytes
1906 field so you can use it to allocate your image memory. This function
1907 will also update your palette with the correct screen_gamma and
1908 background if these have been given with the calls above.
1910 png_read_update_info(png_ptr, info_ptr);
1912 After you call png_read_update_info(), you can allocate any
1913 memory you need to hold the image. The row data is simply
1914 raw byte data for all forms of images. As the actual allocation
1915 varies among applications, no example will be given. If you
1916 are allocating one large chunk, you will need to build an
1917 array of pointers to each row, as it will be needed for some
1918 of the functions below.
1920 .SS Reading image data
1922 After you've allocated memory, you can read the image data.
1923 The simplest way to do this is in one function call. If you are
1924 allocating enough memory to hold the whole image, you can just
1925 call png_read_image() and libpng will read in all the image data
1926 and put it in the memory area supplied. You will need to pass in
1927 an array of pointers to each row.
1929 This function automatically handles interlacing, so you don't need
1930 to call png_set_interlace_handling() or call this function multiple
1931 times, or any of that other stuff necessary with png_read_rows().
1933 png_read_image(png_ptr, row_pointers);
1935 where row_pointers is:
1937 png_bytep row_pointers[height];
1939 You can point to void or char or whatever you use for pixels.
1941 If you don't want to read in the whole image at once, you can
1942 use png_read_rows() instead. If there is no interlacing (check
1943 interlace_type == PNG_INTERLACE_NONE), this is simple:
1945 png_read_rows(png_ptr, row_pointers, NULL,
1948 where row_pointers is the same as in the png_read_image() call.
1950 If you are doing this just one row at a time, you can do this with
1951 a single row_pointer instead of an array of row_pointers:
1953 png_bytep row_pointer = row;
1954 png_read_row(png_ptr, row_pointer, NULL);
1956 If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
1957 get somewhat harder. The only current (PNG Specification version 1.2)
1958 interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
1959 is a somewhat complicated 2D interlace scheme, known as Adam7, that
1960 breaks down an image into seven smaller images of varying size, based
1963 libpng can fill out those images or it can give them to you "as is".
1964 If you want them filled out, there are two ways to do that. The one
1965 mentioned in the PNG specification is to expand each pixel to cover
1966 those pixels that have not been read yet (the "rectangle" method).
1967 This results in a blocky image for the first pass, which gradually
1968 smooths out as more pixels are read. The other method is the "sparkle"
1969 method, where pixels are drawn only in their final locations, with the
1970 rest of the image remaining whatever colors they were initialized to
1971 before the start of the read. The first method usually looks better,
1972 but tends to be slower, as there are more pixels to put in the rows.
1974 If you don't want libpng to handle the interlacing details, just call
1975 png_read_rows() seven times to read in all seven images. Each of the
1976 images is a valid image by itself, or they can all be combined on an
1977 8x8 grid to form a single image (although if you intend to combine them
1978 you would be far better off using the libpng interlace handling).
1980 The first pass will return an image 1/8 as wide as the entire image
1981 (every 8th column starting in column 0) and 1/8 as high as the original
1982 (every 8th row starting in row 0), the second will be 1/8 as wide
1983 (starting in column 4) and 1/8 as high (also starting in row 0). The
1984 third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
1985 1/8 as high (every 8th row starting in row 4), and the fourth pass will
1986 be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
1987 and every 4th row starting in row 0). The fifth pass will return an
1988 image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
1989 while the sixth pass will be 1/2 as wide and 1/2 as high as the original
1990 (starting in column 1 and row 0). The seventh and final pass will be as
1991 wide as the original, and 1/2 as high, containing all of the odd
1992 numbered scanlines. Phew!
1994 If you want libpng to expand the images, call this before calling
1995 png_start_read_image() or png_read_update_info():
1997 if (interlace_type == PNG_INTERLACE_ADAM7)
1999 = png_set_interlace_handling(png_ptr);
2001 This will return the number of passes needed. Currently, this
2002 is seven, but may change if another interlace type is added.
2003 This function can be called even if the file is not interlaced,
2004 where it will return one pass.
2006 If you are not going to display the image after each pass, but are
2007 going to wait until the entire image is read in, use the sparkle
2008 effect. This effect is faster and the end result of either method
2009 is exactly the same. If you are planning on displaying the image
2010 after each pass, the "rectangle" effect is generally considered the
2013 If you only want the "sparkle" effect, just call png_read_rows() as
2014 normal, with the third parameter NULL. Make sure you make pass over
2015 the image number_of_passes times, and you don't change the data in the
2016 rows between calls. You can change the locations of the data, just
2017 not the data. Each pass only writes the pixels appropriate for that
2018 pass, and assumes the data from previous passes is still valid.
2020 png_read_rows(png_ptr, row_pointers, NULL,
2023 If you only want the first effect (the rectangles), do the same as
2024 before except pass the row buffer in the third parameter, and leave
2025 the second parameter NULL.
2027 png_read_rows(png_ptr, NULL, row_pointers,
2030 .SS Finishing a sequential read
2032 After you are finished reading the image through either the high- or
2033 low-level interfaces, you can finish reading the file. If you are
2034 interested in comments or time, which may be stored either before or
2035 after the image data, you should pass the separate png_info struct if
2036 you want to keep the comments from before and after the image
2037 separate. If you are not interested, you can pass NULL.
2039 png_read_end(png_ptr, end_info);
2041 When you are done, you can free all memory allocated by libpng like this:
2043 png_destroy_read_struct(&png_ptr, &info_ptr,
2046 It is also possible to individually free the info_ptr members that
2047 point to libpng-allocated storage with the following function:
2049 png_free_data(png_ptr, info_ptr, mask, seq)
2050 mask - identifies data to be freed, a mask
2051 containing the logical OR of one or
2053 PNG_FREE_PLTE, PNG_FREE_TRNS,
2054 PNG_FREE_HIST, PNG_FREE_ICCP,
2055 PNG_FREE_PCAL, PNG_FREE_ROWS,
2056 PNG_FREE_SCAL, PNG_FREE_SPLT,
2057 PNG_FREE_TEXT, PNG_FREE_UNKN,
2058 or simply PNG_FREE_ALL
2059 seq - sequence number of item to be freed
2062 This function may be safely called when the relevant storage has
2063 already been freed, or has not yet been allocated, or was allocated
2064 by the user and not by libpng, and will in those
2065 cases do nothing. The "seq" parameter is ignored if only one item
2066 of the selected data type, such as PLTE, is allowed. If "seq" is not
2067 -1, and multiple items are allowed for the data type identified in
2068 the mask, such as text or sPLT, only the n'th item in the structure
2069 is freed, where n is "seq".
2071 The default behavior is only to free data that was allocated internally
2072 by libpng. This can be changed, so that libpng will not free the data,
2073 or so that it will free data that was allocated by the user with png_malloc()
2074 or png_zalloc() and passed in via a png_set_*() function, with
2076 png_data_freer(png_ptr, info_ptr, freer, mask)
2077 mask - which data elements are affected
2078 same choices as in png_free_data()
2080 PNG_DESTROY_WILL_FREE_DATA
2081 PNG_SET_WILL_FREE_DATA
2082 PNG_USER_WILL_FREE_DATA
2084 This function only affects data that has already been allocated.
2085 You can call this function after reading the PNG data but before calling
2086 any png_set_*() functions, to control whether the user or the png_set_*()
2087 function is responsible for freeing any existing data that might be present,
2088 and again after the png_set_*() functions to control whether the user
2089 or png_destroy_*() is supposed to free the data. When the user assumes
2090 responsibility for libpng-allocated data, the application must use
2091 png_free() to free it, and when the user transfers responsibility to libpng
2092 for data that the user has allocated, the user must have used png_malloc()
2093 or png_zalloc() to allocate it.
2095 If you allocated your row_pointers in a single block, as suggested above in
2096 the description of the high level read interface, you must not transfer
2097 responsibility for freeing it to the png_set_rows or png_read_destroy function,
2098 because they would also try to free the individual row_pointers[i].
2100 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2101 separately, do not transfer responsibility for freeing text_ptr to libpng,
2102 because when libpng fills a png_text structure it combines these members with
2103 the key member, and png_free_data() will free only text_ptr.key. Similarly,
2104 if you transfer responsibility for free'ing text_ptr from libpng to your
2105 application, your application must not separately free those members.
2107 The png_free_data() function will turn off the "valid" flag for anything
2108 it frees. If you need to turn the flag off for a chunk that was freed by your
2109 application instead of by libpng, you can use
2111 png_set_invalid(png_ptr, info_ptr, mask);
2112 mask - identifies the chunks to be made invalid,
2113 containing the logical OR of one or
2115 PNG_INFO_gAMA, PNG_INFO_sBIT,
2116 PNG_INFO_cHRM, PNG_INFO_PLTE,
2117 PNG_INFO_tRNS, PNG_INFO_bKGD,
2118 PNG_INFO_hIST, PNG_INFO_pHYs,
2119 PNG_INFO_oFFs, PNG_INFO_tIME,
2120 PNG_INFO_pCAL, PNG_INFO_sRGB,
2121 PNG_INFO_iCCP, PNG_INFO_sPLT,
2122 PNG_INFO_sCAL, PNG_INFO_IDAT
2124 For a more compact example of reading a PNG image, see the file example.c.
2126 .SS Reading PNG files progressively
2128 The progressive reader is slightly different then the non-progressive
2129 reader. Instead of calling png_read_info(), png_read_rows(), and
2130 png_read_end(), you make one call to png_process_data(), which calls
2131 callbacks when it has the info, a row, or the end of the image. You
2132 set up these callbacks with png_set_progressive_read_fn(). You don't
2133 have to worry about the input/output functions of libpng, as you are
2134 giving the library the data directly in png_process_data(). I will
2135 assume that you have read the section on reading PNG files above,
2136 so I will only highlight the differences (although I will show
2139 png_structp png_ptr;
2142 /* An example code fragment of how you would
2143 initialize the progressive reader in your
2146 initialize_png_reader()
2148 png_ptr = png_create_read_struct
2149 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2150 user_error_fn, user_warning_fn);
2153 info_ptr = png_create_info_struct(png_ptr);
2156 png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
2161 if (setjmp(png_jmpbuf(png_ptr)))
2163 png_destroy_read_struct(&png_ptr, &info_ptr,
2168 /* This one's new. You can provide functions
2169 to be called when the header info is valid,
2170 when each row is completed, and when the image
2171 is finished. If you aren't using all functions,
2172 you can specify NULL parameters. Even when all
2173 three functions are NULL, you need to call
2174 png_set_progressive_read_fn(). You can use
2175 any struct as the user_ptr (cast to a void pointer
2176 for the function call), and retrieve the pointer
2177 from inside the callbacks using the function
2179 png_get_progressive_ptr(png_ptr);
2181 which will return a void pointer, which you have
2182 to cast appropriately.
2184 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
2185 info_callback, row_callback, end_callback);
2190 /* A code fragment that you call as you receive blocks
2193 process_data(png_bytep buffer, png_uint_32 length)
2195 if (setjmp(png_jmpbuf(png_ptr)))
2197 png_destroy_read_struct(&png_ptr, &info_ptr,
2202 /* This one's new also. Simply give it a chunk
2203 of data from the file stream (in order, of
2204 course). On machines with segmented memory
2205 models machines, don't give it any more than
2206 64K. The library seems to run fine with sizes
2207 of 4K. Although you can give it much less if
2208 necessary (I assume you can give it chunks of
2209 1 byte, I haven't tried less then 256 bytes
2210 yet). When this function returns, you may
2211 want to display any rows that were generated
2212 in the row callback if you don't already do
2215 png_process_data(png_ptr, info_ptr, buffer, length);
2219 /* This function is called (as set by
2220 png_set_progressive_read_fn() above) when enough data
2221 has been supplied so all of the header has been
2225 info_callback(png_structp png_ptr, png_infop info)
2227 /* Do any setup here, including setting any of
2228 the transformations mentioned in the Reading
2229 PNG files section. For now, you _must_ call
2230 either png_start_read_image() or
2231 png_read_update_info() after all the
2232 transformations are set (even if you don't set
2233 any). You may start getting rows before
2234 png_process_data() returns, so this is your
2235 last chance to prepare for that.
2239 /* This function is called when each row of image
2242 row_callback(png_structp png_ptr, png_bytep new_row,
2243 png_uint_32 row_num, int pass)
2245 /* If the image is interlaced, and you turned
2246 on the interlace handler, this function will
2247 be called for every row in every pass. Some
2248 of these rows will not be changed from the
2249 previous pass. When the row is not changed,
2250 the new_row variable will be NULL. The rows
2251 and passes are called in order, so you don't
2252 really need the row_num and pass, but I'm
2253 supplying them because it may make your life
2256 For the non-NULL rows of interlaced images,
2257 you must call png_progressive_combine_row()
2258 passing in the row and the old row. You can
2259 call this function for NULL rows (it will just
2260 return) and for non-interlaced images (it just
2261 does the memcpy for you) if it will make the
2262 code easier. Thus, you can just do this for
2266 png_progressive_combine_row(png_ptr, old_row,
2269 /* where old_row is what was displayed for
2270 previously for the row. Note that the first
2271 pass (pass == 0, really) will completely cover
2272 the old row, so the rows do not have to be
2273 initialized. After the first pass (and only
2274 for interlaced images), you will have to pass
2275 the current row, and the function will combine
2276 the old row and the new row.
2281 end_callback(png_structp png_ptr, png_infop info)
2283 /* This function is called after the whole image
2284 has been read, including any chunks after the
2285 image (up to and including the IEND). You
2286 will usually have the same info chunk as you
2287 had in the header, although some data may have
2288 been added to the comments and time fields.
2290 Most people won't do much here, perhaps setting
2291 a flag that marks the image as finished.
2299 Much of this is very similar to reading. However, everything of
2300 importance is repeated here, so you won't have to constantly look
2301 back up in the reading section to understand writing.
2305 You will want to do the I/O initialization before you get into libpng,
2306 so if it doesn't work, you don't have anything to undo. If you are not
2307 using the standard I/O functions, you will need to replace them with
2308 custom writing functions. See the discussion under Customizing libpng.
2310 FILE *fp = fopen(file_name, "wb");
2316 Next, png_struct and png_info need to be allocated and initialized.
2317 As these can be both relatively large, you may not want to store these
2318 on the stack, unless you have stack space to spare. Of course, you
2319 will want to check if they return NULL. If you are also reading,
2320 you won't want to name your read structure and your write structure
2321 both "png_ptr"; you can call them anything you like, such as
2322 "read_ptr" and "write_ptr". Look at pngtest.c, for example.
2324 png_structp png_ptr = png_create_write_struct
2325 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2326 user_error_fn, user_warning_fn);
2330 png_infop info_ptr = png_create_info_struct(png_ptr);
2333 png_destroy_write_struct(&png_ptr,
2338 If you want to use your own memory allocation routines,
2339 define PNG_USER_MEM_SUPPORTED and use
2340 png_create_write_struct_2() instead of png_create_write_struct():
2342 png_structp png_ptr = png_create_write_struct_2
2343 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2344 user_error_fn, user_warning_fn, (png_voidp)
2345 user_mem_ptr, user_malloc_fn, user_free_fn);
2347 After you have these structures, you will need to set up the
2348 error handling. When libpng encounters an error, it expects to
2349 longjmp() back to your routine. Therefore, you will need to call
2350 setjmp() and pass the png_jmpbuf(png_ptr). If you
2351 write the file from different routines, you will need to update
2352 the png_jmpbuf(png_ptr) every time you enter a new routine that will
2353 call a png_*() function. See your documentation of setjmp/longjmp
2354 for your compiler for more information on setjmp/longjmp. See
2355 the discussion on libpng error handling in the Customizing Libpng
2356 section below for more information on the libpng error handling.
2358 if (setjmp(png_jmpbuf(png_ptr)))
2360 png_destroy_write_struct(&png_ptr, &info_ptr);
2367 If you would rather avoid the complexity of setjmp/longjmp issues,
2368 you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
2369 errors will result in a call to PNG_ABORT() which defaults to abort().
2371 Now you need to set up the output code. The default for libpng is to
2372 use the C function fwrite(). If you use this, you will need to pass a
2373 valid FILE * in the function png_init_io(). Be sure that the file is
2374 opened in binary mode. Again, if you wish to handle writing data in
2375 another way, see the discussion on libpng I/O handling in the Customizing
2376 Libpng section below.
2378 png_init_io(png_ptr, fp);
2382 At this point, you can set up a callback function that will be
2383 called after each row has been written, which you can use to control
2384 a progress meter or the like. It's demonstrated in pngtest.c.
2385 You must supply a function
2387 void write_row_callback(png_ptr, png_uint_32 row,
2390 /* put your code here */
2393 (You can give it another name that you like instead of "write_row_callback")
2395 To inform libpng about your function, use
2397 png_set_write_status_fn(png_ptr, write_row_callback);
2399 You now have the option of modifying how the compression library will
2400 run. The following functions are mainly for testing, but may be useful
2401 in some cases, like if you need to write PNG files extremely fast and
2402 are willing to give up some compression, or if you want to get the
2403 maximum possible compression at the expense of slower writing. If you
2404 have no special needs in this area, let the library do what it wants by
2405 not calling this function at all, as it has been tuned to deliver a good
2406 speed/compression ratio. The second parameter to png_set_filter() is
2407 the filter method, for which the only valid values are 0 (as of the
2408 July 1999 PNG specification, version 1.2) or 64 (if you are writing
2409 a PNG datastream that is to be embedded in a MNG datastream). The third
2410 parameter is a flag that indicates which filter type(s) are to be tested
2411 for each scanline. See the PNG specification for details on the specific filter
2415 /* turn on or off filtering, and/or choose
2416 specific filters. You can use either a single
2417 PNG_FILTER_VALUE_NAME or the logical OR of one
2418 or more PNG_FILTER_NAME masks. */
2419 png_set_filter(png_ptr, 0,
2420 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
2421 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
2422 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
2423 PNG_FILTER_AVE | PNG_FILTER_VALUE_AVE |
2424 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
2428 wants to start and stop using particular filters during compression,
2429 it should start out with all of the filters (to ensure that the previous
2430 row of pixels will be stored in case it's needed later), and then add
2431 and remove them after the start of compression.
2433 If you are writing a PNG datastream that is to be embedded in a MNG
2434 datastream, the second parameter can be either 0 or 64.
2436 The png_set_compression_*() functions interface to the zlib compression
2437 library, and should mostly be ignored unless you really know what you are
2438 doing. The only generally useful call is png_set_compression_level()
2439 which changes how much time zlib spends on trying to compress the image
2440 data. See the Compression Library (zlib.h and algorithm.txt, distributed
2441 with zlib) for details on the compression levels.
2443 /* set the zlib compression level */
2444 png_set_compression_level(png_ptr,
2445 Z_BEST_COMPRESSION);
2447 /* set other zlib parameters */
2448 png_set_compression_mem_level(png_ptr, 8);
2449 png_set_compression_strategy(png_ptr,
2450 Z_DEFAULT_STRATEGY);
2451 png_set_compression_window_bits(png_ptr, 15);
2452 png_set_compression_method(png_ptr, 8);
2453 png_set_compression_buffer_size(png_ptr, 8192)
2455 extern PNG_EXPORT(void,png_set_zbuf_size)
2457 .SS Setting the contents of info for output
2459 You now need to fill in the png_info structure with all the data you
2460 wish to write before the actual image. Note that the only thing you
2461 are allowed to write after the image is the text chunks and the time
2462 chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
2463 the latest PNG specification for more information on that. If you
2464 wish to write them before the image, fill them in now, and flag that
2465 data as being valid. If you want to wait until after the data, don't
2466 fill them until png_write_end(). For all the fields in png_info and
2467 their data types, see png.h. For explanations of what the fields
2468 contain, see the PNG specification.
2470 Some of the more important parts of the png_info are:
2472 png_set_IHDR(png_ptr, info_ptr, width, height,
2473 bit_depth, color_type, interlace_type,
2474 compression_type, filter_method)
2475 width - holds the width of the image
2476 in pixels (up to 2^31).
2477 height - holds the height of the image
2478 in pixels (up to 2^31).
2479 bit_depth - holds the bit depth of one of the
2481 (valid values are 1, 2, 4, 8, 16
2482 and depend also on the
2483 color_type. See also significant
2485 color_type - describes which color/alpha
2486 channels are present.
2488 (bit depths 1, 2, 4, 8, 16)
2489 PNG_COLOR_TYPE_GRAY_ALPHA
2491 PNG_COLOR_TYPE_PALETTE
2492 (bit depths 1, 2, 4, 8)
2495 PNG_COLOR_TYPE_RGB_ALPHA
2498 PNG_COLOR_MASK_PALETTE
2499 PNG_COLOR_MASK_COLOR
2500 PNG_COLOR_MASK_ALPHA
2502 interlace_type - PNG_INTERLACE_NONE or
2504 compression_type - (must be
2505 PNG_COMPRESSION_TYPE_DEFAULT)
2506 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
2507 or, if you are writing a PNG to
2508 be embedded in a MNG datastream,
2510 PNG_INTRAPIXEL_DIFFERENCING)
2512 png_set_PLTE(png_ptr, info_ptr, palette,
2514 palette - the palette for the file
2515 (array of png_color)
2516 num_palette - number of entries in the palette
2518 png_set_gAMA(png_ptr, info_ptr, gamma);
2519 gamma - the gamma the image was created
2522 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
2523 srgb_intent - the rendering intent
2524 (PNG_INFO_sRGB) The presence of
2525 the sRGB chunk means that the pixel
2526 data is in the sRGB color space.
2527 This chunk also implies specific
2528 values of gAMA and cHRM. Rendering
2529 intent is the CSS-1 property that
2530 has been defined by the International
2532 (http://www.color.org).
2534 PNG_sRGB_INTENT_SATURATION,
2535 PNG_sRGB_INTENT_PERCEPTUAL,
2536 PNG_sRGB_INTENT_ABSOLUTE, or
2537 PNG_sRGB_INTENT_RELATIVE.
2540 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
2542 srgb_intent - the rendering intent
2543 (PNG_INFO_sRGB) The presence of the
2544 sRGB chunk means that the pixel
2545 data is in the sRGB color space.
2546 This function also causes gAMA and
2547 cHRM chunks with the specific values
2548 that are consistent with sRGB to be
2551 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
2553 name - The profile name.
2554 compression - The compression type; always
2555 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2556 You may give NULL to this argument to
2558 profile - International Color Consortium color
2559 profile data. May contain NULs.
2560 proflen - length of profile data in bytes.
2562 png_set_sBIT(png_ptr, info_ptr, sig_bit);
2563 sig_bit - the number of significant bits for
2564 (PNG_INFO_sBIT) each of the gray, red,
2565 green, and blue channels, whichever are
2566 appropriate for the given color type
2569 png_set_tRNS(png_ptr, info_ptr, trans, num_trans,
2571 trans - array of transparent entries for
2572 palette (PNG_INFO_tRNS)
2573 trans_values - graylevel or color sample values of
2574 the single transparent color for
2575 non-paletted images (PNG_INFO_tRNS)
2576 num_trans - number of transparent entries
2579 png_set_hIST(png_ptr, info_ptr, hist);
2581 hist - histogram of palette (array of
2584 png_set_tIME(png_ptr, info_ptr, mod_time);
2585 mod_time - time image was last modified
2588 png_set_bKGD(png_ptr, info_ptr, background);
2589 background - background color (PNG_VALID_bKGD)
2591 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
2592 text_ptr - array of png_text holding image
2594 text_ptr[i].compression - type of compression used
2595 on "text" PNG_TEXT_COMPRESSION_NONE
2596 PNG_TEXT_COMPRESSION_zTXt
2597 PNG_ITXT_COMPRESSION_NONE
2598 PNG_ITXT_COMPRESSION_zTXt
2599 text_ptr[i].key - keyword for comment. Must contain
2601 text_ptr[i].text - text comments for current
2602 keyword. Can be NULL or empty.
2603 text_ptr[i].text_length - length of text string,
2604 after decompression, 0 for iTXt
2605 text_ptr[i].itxt_length - length of itxt string,
2606 after decompression, 0 for tEXt/zTXt
2607 text_ptr[i].lang - language of comment (NULL or
2609 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
2610 or empty for unknown).
2611 num_text - number of comments
2613 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
2615 palette_ptr - array of png_sPLT_struct structures
2616 to be added to the list of palettes
2617 in the info structure.
2618 num_spalettes - number of palette structures to be
2621 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
2623 offset_x - positive offset from the left
2625 offset_y - positive offset from the top
2627 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2629 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
2631 res_x - pixels/unit physical resolution
2633 res_y - pixels/unit physical resolution
2635 unit_type - PNG_RESOLUTION_UNKNOWN,
2636 PNG_RESOLUTION_METER
2638 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
2639 unit - physical scale units (an integer)
2640 width - width of a pixel in physical scale units
2641 height - height of a pixel in physical scale units
2642 (width and height are doubles)
2644 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
2645 unit - physical scale units (an integer)
2646 width - width of a pixel in physical scale units
2647 height - height of a pixel in physical scale units
2648 (width and height are strings like "2.54")
2650 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
2652 unknowns - array of png_unknown_chunk
2653 structures holding unknown chunks
2654 unknowns[i].name - name of unknown chunk
2655 unknowns[i].data - data of unknown chunk
2656 unknowns[i].size - size of unknown chunk's data
2657 unknowns[i].location - position to write chunk in file
2658 0: do not write chunk
2659 PNG_HAVE_IHDR: before PLTE
2660 PNG_HAVE_PLTE: before IDAT
2661 PNG_AFTER_IDAT: after IDAT
2663 The "location" member is set automatically according to
2664 what part of the output file has already been written.
2665 You can change its value after calling png_set_unknown_chunks()
2666 as demonstrated in pngtest.c. Within each of the "locations",
2667 the chunks are sequenced according to their position in the
2668 structure (that is, the value of "i", which is the order in which
2669 the chunk was either read from the input file or defined with
2670 png_set_unknown_chunks).
2672 A quick word about text and num_text. text is an array of png_text
2673 structures. num_text is the number of valid structures in the array.
2674 Each png_text structure holds a language code, a keyword, a text value,
2675 and a compression type.
2677 The compression types have the same valid numbers as the compression
2678 types of the image data. Currently, the only valid number is zero.
2679 However, you can store text either compressed or uncompressed, unlike
2680 images, which always have to be compressed. So if you don't want the
2681 text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
2682 Because tEXt and zTXt chunks don't have a language field, if you
2683 specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
2684 any language code or translated keyword will not be written out.
2686 Until text gets around 1000 bytes, it is not worth compressing it.
2687 After the text has been written out to the file, the compression type
2688 is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
2689 so that it isn't written out again at the end (in case you are calling
2690 png_write_end() with the same struct.
2692 The keywords that are given in the PNG Specification are:
2694 Title Short (one line) title or
2696 Author Name of image's creator
2697 Description Description of image (possibly long)
2698 Copyright Copyright notice
2699 Creation Time Time of original image creation
2700 (usually RFC 1123 format, see below)
2701 Software Software used to create the image
2702 Disclaimer Legal disclaimer
2703 Warning Warning of nature of content
2704 Source Device used to create the image
2705 Comment Miscellaneous comment; conversion
2706 from other image format
2708 The keyword-text pairs work like this. Keywords should be short
2709 simple descriptions of what the comment is about. Some typical
2710 keywords are found in the PNG specification, as is some recommendations
2711 on keywords. You can repeat keywords in a file. You can even write
2712 some text before the image and some after. For example, you may want
2713 to put a description of the image before the image, but leave the
2714 disclaimer until after, so viewers working over modem connections
2715 don't have to wait for the disclaimer to go over the modem before
2716 they start seeing the image. Finally, keywords should be full
2717 words, not abbreviations. Keywords and text are in the ISO 8859-1
2718 (Latin-1) character set (a superset of regular ASCII) and can not
2719 contain NUL characters, and should not contain control or other
2720 unprintable characters. To make the comments widely readable, stick
2721 with basic ASCII, and avoid machine specific character set extensions
2722 like the IBM-PC character set. The keyword must be present, but
2723 you can leave off the text string on non-compressed pairs.
2724 Compressed pairs must have a text string, as only the text string
2725 is compressed anyway, so the compression would be meaningless.
2727 PNG supports modification time via the png_time structure. Two
2728 conversion routines are provided, png_convert_from_time_t() for
2729 time_t and png_convert_from_struct_tm() for struct tm. The
2730 time_t routine uses gmtime(). You don't have to use either of
2731 these, but if you wish to fill in the png_time structure directly,
2732 you should provide the time in universal time (GMT) if possible
2733 instead of your local time. Note that the year number is the full
2734 year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
2735 that months start with 1.
2737 If you want to store the time of the original image creation, you should
2738 use a plain tEXt chunk with the "Creation Time" keyword. This is
2739 necessary because the "creation time" of a PNG image is somewhat vague,
2740 depending on whether you mean the PNG file, the time the image was
2741 created in a non-PNG format, a still photo from which the image was
2742 scanned, or possibly the subject matter itself. In order to facilitate
2743 machine-readable dates, it is recommended that the "Creation Time"
2744 tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
2745 although this isn't a requirement. Unlike the tIME chunk, the
2746 "Creation Time" tEXt chunk is not expected to be automatically changed
2747 by the software. To facilitate the use of RFC 1123 dates, a function
2748 png_convert_to_rfc1123(png_timep) is provided to convert from PNG
2749 time to an RFC 1123 format string.
2751 .SS Writing unknown chunks
2753 You can use the png_set_unknown_chunks function to queue up chunks
2754 for writing. You give it a chunk name, raw data, and a size; that's
2755 all there is to it. The chunks will be written by the next following
2756 png_write_info_before_PLTE, png_write_info, or png_write_end function.
2757 Any chunks previously read into the info structure's unknown-chunk
2758 list will also be written out in a sequence that satisfies the PNG
2759 specification's ordering rules.
2761 .SS The high-level write interface
2763 At this point there are two ways to proceed; through the high-level
2764 write interface, or through a sequence of low-level write operations.
2765 You can use the high-level interface if your image data is present
2766 in the info structure. All defined output
2767 transformations are permitted, enabled by the following masks.
2769 PNG_TRANSFORM_IDENTITY No transformation
2770 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
2771 PNG_TRANSFORM_PACKSWAP Change order of packed
2773 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
2774 PNG_TRANSFORM_SHIFT Normalize pixels to the
2776 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
2778 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
2780 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
2782 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
2783 PNG_TRANSFORM_STRIP_FILLER Strip out filler bytes.
2785 If you have valid image data in the info structure (you can use
2786 png_set_rows() to put image data in the info structure), simply do this:
2788 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
2790 where png_transforms is an integer containing the logical OR of some set of
2791 transformation flags. This call is equivalent to png_write_info(),
2792 followed the set of transformations indicated by the transform mask,
2793 then png_write_image(), and finally png_write_end().
2795 (The final parameter of this call is not yet used. Someday it might point
2796 to transformation parameters required by some future output transform.)
2798 You must use png_transforms and not call any png_set_transform() functions
2799 when you use png_write_png().
2801 .SS The low-level write interface
2803 If you are going the low-level route instead, you are now ready to
2804 write all the file information up to the actual image data. You do
2805 this with a call to png_write_info().
2807 png_write_info(png_ptr, info_ptr);
2809 Note that there is one transformation you may need to do before
2810 png_write_info(). In PNG files, the alpha channel in an image is the
2811 level of opacity. If your data is supplied as a level of
2812 transparency, you can invert the alpha channel before you write it, so
2813 that 0 is fully transparent and 255 (in 8-bit or paletted images) or
2814 65535 (in 16-bit images) is fully opaque, with
2816 png_set_invert_alpha(png_ptr);
2818 This must appear before png_write_info() instead of later with the
2819 other transformations because in the case of paletted images the tRNS
2820 chunk data has to be inverted before the tRNS chunk is written. If
2821 your image is not a paletted image, the tRNS data (which in such cases
2822 represents a single color to be rendered as transparent) won't need to
2823 be changed, and you can safely do this transformation after your
2824 png_write_info() call.
2826 If you need to write a private chunk that you want to appear before
2827 the PLTE chunk when PLTE is present, you can write the PNG info in
2828 two steps, and insert code to write your own chunk between them:
2830 png_write_info_before_PLTE(png_ptr, info_ptr);
2831 png_set_unknown_chunks(png_ptr, info_ptr, ...);
2832 png_write_info(png_ptr, info_ptr);
2834 After you've written the file information, you can set up the library
2835 to handle any special transformations of the image data. The various
2836 ways to transform the data will be described in the order that they
2837 should occur. This is important, as some of these change the color
2838 type and/or bit depth of the data, and some others only work on
2839 certain color types and bit depths. Even though each transformation
2840 checks to see if it has data that it can do something with, you should
2841 make sure to only enable a transformation if it will be valid for the
2842 data. For example, don't swap red and blue on grayscale data.
2844 PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
2845 the library to strip input data that has 4 or 8 bytes per pixel down
2846 to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
2849 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
2851 where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
2852 PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
2853 is stored XRGB or RGBX.
2855 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2856 they can, resulting in, for example, 8 pixels per byte for 1 bit files.
2857 If the data is supplied at 1 pixel per byte, use this code, which will
2858 correctly pack the pixels into a single byte:
2860 png_set_packing(png_ptr);
2862 PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
2863 data is of another bit depth, you can write an sBIT chunk into the
2864 file so that decoders can recover the original data if desired.
2866 /* Set the true bit depth of the image data */
2867 if (color_type & PNG_COLOR_MASK_COLOR)
2869 sig_bit.red = true_bit_depth;
2870 sig_bit.green = true_bit_depth;
2871 sig_bit.blue = true_bit_depth;
2875 sig_bit.gray = true_bit_depth;
2877 if (color_type & PNG_COLOR_MASK_ALPHA)
2879 sig_bit.alpha = true_bit_depth;
2882 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
2884 If the data is stored in the row buffer in a bit depth other than
2885 one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
2886 this will scale the values to appear to be the correct bit depth as
2889 png_set_shift(png_ptr, &sig_bit);
2891 PNG files store 16 bit pixels in network byte order (big-endian,
2892 ie. most significant bits first). This code would be used if they are
2893 supplied the other way (little-endian, i.e. least significant bits
2894 first, the way PCs store them):
2897 png_set_swap(png_ptr);
2899 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2900 need to change the order the pixels are packed into bytes, you can use:
2903 png_set_packswap(png_ptr);
2905 PNG files store 3 color pixels in red, green, blue order. This code
2906 would be used if they are supplied as blue, green, red:
2908 png_set_bgr(png_ptr);
2910 PNG files describe monochrome as black being zero and white being
2911 one. This code would be used if the pixels are supplied with this reversed
2912 (black being one and white being zero):
2914 png_set_invert_mono(png_ptr);
2916 Finally, you can write your own transformation function if none of
2917 the existing ones meets your needs. This is done by setting a callback
2920 png_set_write_user_transform_fn(png_ptr,
2921 write_transform_fn);
2923 You must supply the function
2925 void write_transform_fn(png_ptr ptr, row_info_ptr
2926 row_info, png_bytep data)
2928 See pngtest.c for a working example. Your function will be called
2929 before any of the other transformations are processed.
2931 You can also set up a pointer to a user structure for use by your
2934 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
2936 The user_channels and user_depth parameters of this function are ignored
2937 when writing; you can set them to zero as shown.
2939 You can retrieve the pointer via the function png_get_user_transform_ptr().
2942 voidp write_user_transform_ptr =
2943 png_get_user_transform_ptr(png_ptr);
2945 It is possible to have libpng flush any pending output, either manually,
2946 or automatically after a certain number of lines have been written. To
2947 flush the output stream a single time call:
2949 png_write_flush(png_ptr);
2951 and to have libpng flush the output stream periodically after a certain
2952 number of scanlines have been written, call:
2954 png_set_flush(png_ptr, nrows);
2956 Note that the distance between rows is from the last time png_write_flush()
2957 was called, or the first row of the image if it has never been called.
2958 So if you write 50 lines, and then png_set_flush 25, it will flush the
2959 output on the next scanline, and every 25 lines thereafter, unless
2960 png_write_flush() is called before 25 more lines have been written.
2961 If nrows is too small (less than about 10 lines for a 640 pixel wide
2962 RGB image) the image compression may decrease noticeably (although this
2963 may be acceptable for real-time applications). Infrequent flushing will
2964 only degrade the compression performance by a few percent over images
2965 that do not use flushing.
2967 .SS Writing the image data
2969 That's it for the transformations. Now you can write the image data.
2970 The simplest way to do this is in one function call. If you have the
2971 whole image in memory, you can just call png_write_image() and libpng
2972 will write the image. You will need to pass in an array of pointers to
2973 each row. This function automatically handles interlacing, so you don't
2974 need to call png_set_interlace_handling() or call this function multiple
2975 times, or any of that other stuff necessary with png_write_rows().
2977 png_write_image(png_ptr, row_pointers);
2979 where row_pointers is:
2981 png_byte *row_pointers[height];
2983 You can point to void or char or whatever you use for pixels.
2985 If you don't want to write the whole image at once, you can
2986 use png_write_rows() instead. If the file is not interlaced,
2989 png_write_rows(png_ptr, row_pointers,
2992 row_pointers is the same as in the png_write_image() call.
2994 If you are just writing one row at a time, you can do this with
2995 a single row_pointer instead of an array of row_pointers:
2997 png_bytep row_pointer = row;
2999 png_write_row(png_ptr, row_pointer);
3001 When the file is interlaced, things can get a good deal more
3002 complicated. The only currently (as of the PNG Specification
3003 version 1.2, dated July 1999) defined interlacing scheme for PNG files
3004 is the "Adam7" interlace scheme, that breaks down an
3005 image into seven smaller images of varying size. libpng will build
3006 these images for you, or you can do them yourself. If you want to
3007 build them yourself, see the PNG specification for details of which
3008 pixels to write when.
3010 If you don't want libpng to handle the interlacing details, just
3011 use png_set_interlace_handling() and call png_write_rows() the
3012 correct number of times to write all seven sub-images.
3014 If you want libpng to build the sub-images, call this before you start
3018 png_set_interlace_handling(png_ptr);
3020 This will return the number of passes needed. Currently, this
3021 is seven, but may change if another interlace type is added.
3023 Then write the complete image number_of_passes times.
3025 png_write_rows(png_ptr, row_pointers,
3028 As some of these rows are not used, and thus return immediately,
3029 you may want to read about interlacing in the PNG specification,
3030 and only update the rows that are actually used.
3032 .SS Finishing a sequential write
3034 After you are finished writing the image, you should finish writing
3035 the file. If you are interested in writing comments or time, you should
3036 pass an appropriately filled png_info pointer. If you are not interested,
3039 png_write_end(png_ptr, info_ptr);
3041 When you are done, you can free all memory used by libpng like this:
3043 png_destroy_write_struct(&png_ptr, &info_ptr);
3045 It is also possible to individually free the info_ptr members that
3046 point to libpng-allocated storage with the following function:
3048 png_free_data(png_ptr, info_ptr, mask, seq)
3049 mask - identifies data to be freed, a mask
3050 containing the logical OR of one or
3052 PNG_FREE_PLTE, PNG_FREE_TRNS,
3053 PNG_FREE_HIST, PNG_FREE_ICCP,
3054 PNG_FREE_PCAL, PNG_FREE_ROWS,
3055 PNG_FREE_SCAL, PNG_FREE_SPLT,
3056 PNG_FREE_TEXT, PNG_FREE_UNKN,
3057 or simply PNG_FREE_ALL
3058 seq - sequence number of item to be freed
3061 This function may be safely called when the relevant storage has
3062 already been freed, or has not yet been allocated, or was allocated
3063 by the user and not by libpng, and will in those
3064 cases do nothing. The "seq" parameter is ignored if only one item
3065 of the selected data type, such as PLTE, is allowed. If "seq" is not
3066 -1, and multiple items are allowed for the data type identified in
3067 the mask, such as text or sPLT, only the n'th item in the structure
3068 is freed, where n is "seq".
3070 If you allocated data such as a palette that you passed
3071 in to libpng with png_set_*, you must not free it until just before the call to
3072 png_destroy_write_struct().
3074 The default behavior is only to free data that was allocated internally
3075 by libpng. This can be changed, so that libpng will not free the data,
3076 or so that it will free data that was allocated by the user with png_malloc()
3077 or png_zalloc() and passed in via a png_set_*() function, with
3079 png_data_freer(png_ptr, info_ptr, freer, mask)
3080 mask - which data elements are affected
3081 same choices as in png_free_data()
3083 PNG_DESTROY_WILL_FREE_DATA
3084 PNG_SET_WILL_FREE_DATA
3085 PNG_USER_WILL_FREE_DATA
3087 For example, to transfer responsibility for some data from a read structure
3088 to a write structure, you could use
3090 png_data_freer(read_ptr, read_info_ptr,
3091 PNG_USER_WILL_FREE_DATA,
3092 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3093 png_data_freer(write_ptr, write_info_ptr,
3094 PNG_DESTROY_WILL_FREE_DATA,
3095 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3097 thereby briefly reassigning responsibility for freeing to the user but
3098 immediately afterwards reassigning it once more to the write_destroy
3099 function. Having done this, it would then be safe to destroy the read
3100 structure and continue to use the PLTE, tRNS, and hIST data in the write
3103 This function only affects data that has already been allocated.
3104 You can call this function before calling after the png_set_*() functions
3105 to control whether the user or png_destroy_*() is supposed to free the data.
3106 When the user assumes responsibility for libpng-allocated data, the
3107 application must use
3108 png_free() to free it, and when the user transfers responsibility to libpng
3109 for data that the user has allocated, the user must have used png_malloc()
3110 or png_zalloc() to allocate it.
3112 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3113 separately, do not transfer responsibility for freeing text_ptr to libpng,
3114 because when libpng fills a png_text structure it combines these members with
3115 the key member, and png_free_data() will free only text_ptr.key. Similarly,
3116 if you transfer responsibility for free'ing text_ptr from libpng to your
3117 application, your application must not separately free those members.
3118 For a more compact example of writing a PNG image, see the file example.c.
3120 .SH V. Modifying/Customizing libpng:
3122 There are three issues here. The first is changing how libpng does
3123 standard things like memory allocation, input/output, and error handling.
3124 The second deals with more complicated things like adding new chunks,
3125 adding new transformations, and generally changing how libpng works.
3126 Both of those are compile-time issues; that is, they are generally
3127 determined at the time the code is written, and there is rarely a need
3128 to provide the user with a means of changing them. The third is a
3129 run-time issue: choosing between and/or tuning one or more alternate
3130 versions of computationally intensive routines; specifically, optimized
3131 assembly-language (and therefore compiler- and platform-dependent)
3134 Memory allocation, input/output, and error handling
3136 All of the memory allocation, input/output, and error handling in libpng
3137 goes through callbacks that are user-settable. The default routines are
3138 in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
3139 these functions, call the appropriate png_set_*_fn() function.
3141 Memory allocation is done through the functions png_malloc()
3142 and png_free(). These currently just call the standard C functions. If
3143 your pointers can't access more then 64K at a time, you will want to set
3144 MAXSEG_64K in zlib.h. Since it is unlikely that the method of handling
3145 memory allocation on a platform will change between applications, these
3146 functions must be modified in the library at compile time. If you prefer
3147 to use a different method of allocating and freeing data, you can use
3148 png_create_read_struct_2() or png_create_write_struct_2() to register
3149 your own functions as described above.
3150 These functions also provide a void pointer that can be retrieved via
3152 mem_ptr=png_get_mem_ptr(png_ptr);
3154 Your replacement memory functions must have prototypes as follows:
3156 png_voidp malloc_fn(png_structp png_ptr,
3158 void free_fn(png_structp png_ptr, png_voidp ptr);
3160 Your malloc_fn() must return NULL in case of failure. The png_malloc()
3161 function will normally call png_error() if it receives a NULL from the
3162 system memory allocator or from your replacement malloc_fn().
3164 Input/Output in libpng is done through png_read() and png_write(),
3165 which currently just call fread() and fwrite(). The FILE * is stored in
3166 png_struct and is initialized via png_init_io(). If you wish to change
3167 the method of I/O, the library supplies callbacks that you can set
3168 through the function png_set_read_fn() and png_set_write_fn() at run
3169 time, instead of calling the png_init_io() function. These functions
3170 also provide a void pointer that can be retrieved via the function
3171 png_get_io_ptr(). For example:
3173 png_set_read_fn(png_structp read_ptr,
3174 voidp read_io_ptr, png_rw_ptr read_data_fn)
3176 png_set_write_fn(png_structp write_ptr,
3177 voidp write_io_ptr, png_rw_ptr write_data_fn,
3178 png_flush_ptr output_flush_fn);
3180 voidp read_io_ptr = png_get_io_ptr(read_ptr);
3181 voidp write_io_ptr = png_get_io_ptr(write_ptr);
3183 The replacement I/O functions must have prototypes as follows:
3185 void user_read_data(png_structp png_ptr,
3186 png_bytep data, png_size_t length);
3187 void user_write_data(png_structp png_ptr,
3188 png_bytep data, png_size_t length);
3189 void user_flush_data(png_structp png_ptr);
3191 Supplying NULL for the read, write, or flush functions sets them back
3192 to using the default C stream functions. It is an error to read from
3193 a write stream, and vice versa.
3195 Error handling in libpng is done through png_error() and png_warning().
3196 Errors handled through png_error() are fatal, meaning that png_error()
3197 should never return to its caller. Currently, this is handled via
3198 setjmp() and longjmp() (unless you have compiled libpng with
3199 PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()),
3200 but you could change this to do things like exit() if you should wish.
3202 On non-fatal errors, png_warning() is called
3203 to print a warning message, and then control returns to the calling code.
3204 By default png_error() and png_warning() print a message on stderr via
3205 fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
3206 (because you don't want the messages) or PNG_NO_STDIO defined (because
3207 fprintf() isn't available). If you wish to change the behavior of the error
3208 functions, you will need to set up your own message callbacks. These
3209 functions are normally supplied at the time that the png_struct is created.
3210 It is also possible to redirect errors and warnings to your own replacement
3211 functions after png_create_*_struct() has been called by calling:
3213 png_set_error_fn(png_structp png_ptr,
3214 png_voidp error_ptr, png_error_ptr error_fn,
3215 png_error_ptr warning_fn);
3217 png_voidp error_ptr = png_get_error_ptr(png_ptr);
3219 If NULL is supplied for either error_fn or warning_fn, then the libpng
3220 default function will be used, calling fprintf() and/or longjmp() if a
3221 problem is encountered. The replacement error functions should have
3222 parameters as follows:
3224 void user_error_fn(png_structp png_ptr,
3225 png_const_charp error_msg);
3226 void user_warning_fn(png_structp png_ptr,
3227 png_const_charp warning_msg);
3229 The motivation behind using setjmp() and longjmp() is the C++ throw and
3230 catch exception handling methods. This makes the code much easier to write,
3231 as there is no need to check every return code of every function call.
3232 However, there are some uncertainties about the status of local variables
3233 after a longjmp, so the user may want to be careful about doing anything after
3234 setjmp returns non-zero besides returning itself. Consult your compiler
3235 documentation for more details. For an alternative approach, you may wish
3236 to use the "cexcept" facility (see http://cexcept.sourceforge.net).
3240 If you need to read or write custom chunks, you may need to get deeper
3241 into the libpng code. The library now has mechanisms for storing
3242 and writing chunks of unknown type; you can even declare callbacks
3243 for custom chunks. Hoewver, this may not be good enough if the
3244 library code itself needs to know about interactions between your
3245 chunk and existing `intrinsic' chunks.
3247 If you need to write a new intrinsic chunk, first read the PNG
3248 specification. Acquire a first level of
3249 understanding of how it works. Pay particular attention to the
3250 sections that describe chunk names, and look at how other chunks were
3251 designed, so you can do things similarly. Second, check out the
3252 sections of libpng that read and write chunks. Try to find a chunk
3253 that is similar to yours and use it as a template. More details can
3254 be found in the comments inside the code. It is best to handle unknown
3255 chunks in a generic method, via callback functions, instead of by
3256 modifying libpng functions.
3258 If you wish to write your own transformation for the data, look through
3259 the part of the code that does the transformations, and check out some of
3260 the simpler ones to get an idea of how they work. Try to find a similar
3261 transformation to the one you want to add and copy off of it. More details
3262 can be found in the comments inside the code itself.
3264 .SS Configuring for 16 bit platforms
3266 You will want to look into zconf.h to tell zlib (and thus libpng) that
3267 it cannot allocate more then 64K at a time. Even if you can, the memory
3268 won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
3270 .SS Configuring for DOS
3272 For DOS users who only have access to the lower 640K, you will
3273 have to limit zlib's memory usage via a png_set_compression_mem_level()
3274 call. See zlib.h or zconf.h in the zlib library for more information.
3276 .SS Configuring for Medium Model
3278 Libpng's support for medium model has been tested on most of the popular
3279 compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
3280 defined, and FAR gets defined to far in pngconf.h, and you should be
3281 all set. Everything in the library (except for zlib's structure) is
3282 expecting far data. You must use the typedefs with the p or pp on
3283 the end for pointers (or at least look at them and be careful). Make
3284 note that the rows of data are defined as png_bytepp, which is an
3285 unsigned char far * far *.
3287 .SS Configuring for gui/windowing platforms:
3289 You will need to write new error and warning functions that use the GUI
3290 interface, as described previously, and set them to be the error and
3291 warning functions at the time that png_create_*_struct() is called,
3292 in order to have them available during the structure initialization.
3293 They can be changed later via png_set_error_fn(). On some compilers,
3294 you may also have to change the memory allocators (png_malloc, etc.).
3296 .SS Configuring for compiler xxx:
3298 All includes for libpng are in pngconf.h. If you need to add/change/delete
3299 an include, this is the place to do it. The includes that are not
3300 needed outside libpng are protected by the PNG_INTERNAL definition,
3301 which is only defined for those routines inside libpng itself. The
3302 files in libpng proper only include png.h, which includes pngconf.h.
3304 .SS Configuring zlib:
3306 There are special functions to configure the compression. Perhaps the
3307 most useful one changes the compression level, which currently uses
3308 input compression values in the range 0 - 9. The library normally
3309 uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
3310 have shown that for a large majority of images, compression values in
3311 the range 3-6 compress nearly as well as higher levels, and do so much
3312 faster. For online applications it may be desirable to have maximum speed
3313 (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
3314 specify no compression (Z_NO_COMPRESSION = 0), but this would create
3315 files larger than just storing the raw bitmap. You can specify the
3316 compression level by calling:
3318 png_set_compression_level(png_ptr, level);
3320 Another useful one is to reduce the memory level used by the library.
3321 The memory level defaults to 8, but it can be lowered if you are
3322 short on memory (running DOS, for example, where you only have 640K).
3323 Note that the memory level does have an effect on compression; among
3324 other things, lower levels will result in sections of incompressible
3325 data being emitted in smaller stored blocks, with a correspondingly
3326 larger relative overhead of up to 15% in the worst case.
3328 png_set_compression_mem_level(png_ptr, level);
3330 The other functions are for configuring zlib. They are not recommended
3331 for normal use and may result in writing an invalid PNG file. See
3332 zlib.h for more information on what these mean.
3334 png_set_compression_strategy(png_ptr,
3336 png_set_compression_window_bits(png_ptr,
3338 png_set_compression_method(png_ptr, method);
3339 png_set_compression_buffer_size(png_ptr, size);
3341 .SS Controlling row filtering
3343 If you want to control whether libpng uses filtering or not, which
3344 filters are used, and how it goes about picking row filters, you
3345 can call one of these functions. The selection and configuration
3346 of row filters can have a significant impact on the size and
3347 encoding speed and a somewhat lesser impact on the decoding speed
3348 of an image. Filtering is enabled by default for RGB and grayscale
3349 images (with and without alpha), but not for paletted images nor
3350 for any images with bit depths less than 8 bits/pixel.
3352 The 'method' parameter sets the main filtering method, which is
3353 currently only '0' in the PNG 1.2 specification. The 'filters'
3354 parameter sets which filter(s), if any, should be used for each
3355 scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
3356 to turn filtering on and off, respectively.
3358 Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
3359 PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
3360 ORed together with '|' to specify one or more filters to use.
3361 These filters are described in more detail in the PNG specification.
3362 If you intend to change the filter type during the course of writing
3363 the image, you should start with flags set for all of the filters
3364 you intend to use so that libpng can initialize its internal
3365 structures appropriately for all of the filter types. (Note that this
3366 means the first row must always be adaptively filtered, because libpng
3367 currently does not allocate the filter buffers until png_write_row()
3368 is called for the first time.)
3370 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
3371 PNG_FILTER_UP | PNG_FILTER_AVE |
3372 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
3374 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
3376 The second parameter can also be
3377 PNG_INTRAPIXEL_DIFFERENCING if you are
3378 writing a PNG to be embedded in a MNG
3379 datastream. This parameter must be the
3380 same as the value of filter_method used
3383 It is also possible to influence how libpng chooses from among the
3384 available filters. This is done in one or both of two ways - by
3385 telling it how important it is to keep the same filter for successive
3386 rows, and by telling it the relative computational costs of the filters.
3388 double weights[3] = {1.5, 1.3, 1.1},
3389 costs[PNG_FILTER_VALUE_LAST] =
3390 {1.0, 1.3, 1.3, 1.5, 1.7};
3392 png_set_filter_heuristics(png_ptr,
3393 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
3396 The weights are multiplying factors that indicate to libpng that the
3397 row filter should be the same for successive rows unless another row filter
3398 is that many times better than the previous filter. In the above example,
3399 if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
3400 "sum of absolute differences" 1.5 x 1.3 times higher than other filters
3401 and still be chosen, while the NONE filter could have a sum 1.1 times
3402 higher than other filters and still be chosen. Unspecified weights are
3403 taken to be 1.0, and the specified weights should probably be declining
3404 like those above in order to emphasize recent filters over older filters.
3406 The filter costs specify for each filter type a relative decoding cost
3407 to be considered when selecting row filters. This means that filters
3408 with higher costs are less likely to be chosen over filters with lower
3409 costs, unless their "sum of absolute differences" is that much smaller.
3410 The costs do not necessarily reflect the exact computational speeds of
3411 the various filters, since this would unduly influence the final image
3414 Note that the numbers above were invented purely for this example and
3415 are given only to help explain the function usage. Little testing has
3416 been done to find optimum values for either the costs or the weights.
3418 .SS Removing unwanted object code
3420 There are a bunch of #define's in pngconf.h that control what parts of
3421 libpng are compiled. All the defines end in _SUPPORTED. If you are
3422 never going to use a capability, you can change the #define to #undef
3423 before recompiling libpng and save yourself code and data space, or
3424 you can turn off individual capabilities with defines that begin with
3427 You can also turn all of the transforms and ancillary chunk capabilities
3428 off en masse with compiler directives that define
3429 PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
3431 along with directives to turn on any of the capabilities that you do
3432 want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable
3433 the extra transformations but still leave the library fully capable of reading
3434 and writing PNG files with all known public chunks
3435 Use of the PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive
3436 produces a library that is incapable of reading or writing ancillary chunks.
3437 If you are not using the progressive reading capability, you can
3438 turn that off with PNG_NO_PROGRESSIVE_READ (don't confuse
3439 this with the INTERLACING capability, which you'll still have).
3441 All the reading and writing specific code are in separate files, so the
3442 linker should only grab the files it needs. However, if you want to
3443 make sure, or if you are building a stand alone library, all the
3444 reading files start with pngr and all the writing files start with
3445 pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
3446 are used for both reading and writing, and always need to be included.
3447 The progressive reader is in pngpread.c
3449 If you are creating or distributing a dynamically linked library (a .so
3450 or DLL file), you should not remove or disable any parts of the library,
3451 as this will cause applications linked with different versions of the
3452 library to fail if they call functions not available in your library.
3453 The size of the library itself should not be an issue, because only
3454 those sections that are actually used will be loaded into memory.
3456 .SS Requesting debug printout
3458 The macro definition PNG_DEBUG can be used to request debugging
3459 printout. Set it to an integer value in the range 0 to 3. Higher
3460 numbers result in increasing amounts of debugging information. The
3461 information is printed to the "stderr" file, unless another file
3462 name is specified in the PNG_DEBUG_FILE macro definition.
3464 When PNG_DEBUG > 0, the following functions (macros) become available:
3466 png_debug(level, message)
3467 png_debug1(level, message, p1)
3468 png_debug2(level, message, p1, p2)
3470 in which "level" is compared to PNG_DEBUG to decide whether to print
3471 the message, "message" is the formatted string to be printed,
3472 and p1 and p2 are parameters that are to be embedded in the string
3473 according to printf-style formatting directives. For example,
3475 png_debug1(2, "foo=%d\n", foo);
3480 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
3482 When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
3483 can still use PNG_DEBUG to control your own debugging:
3489 When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
3490 having level = 0 will be printed. There aren't any such statements in
3491 this version of libpng, but if you insert some they will be printed.
3493 .SH VI. Runtime optimization
3495 A new feature in libpng 1.2.0 is the ability to dynamically switch between
3496 standard and optimized versions of some routines. Currently these are
3497 limited to three computationally intensive tasks when reading PNG files:
3498 decoding row filters, expanding interlacing, and combining interlaced or
3499 transparent row data with previous row data. Currently the optimized
3500 versions are available only for x86 (Intel, AMD, etc.) platforms with
3501 MMX support, though this may change in future versions. (For example,
3502 the non-MMX assembler optimizations for zlib might become similarly
3503 runtime-selectable in future releases, in which case libpng could be
3504 extended to support them. Alternatively, the compile-time choice of
3505 floating-point versus integer routines for gamma correction might become
3506 runtime-selectable.)
3508 Because such optimizations tend to be very platform- and compiler-dependent,
3509 both in how they are written and in how they perform, the new runtime code
3510 in libpng has been written to allow programs to query, enable, and disable
3511 either specific optimizations or all such optimizations. For example, to
3512 enable all possible optimizations (bearing in mind that some "optimizations"
3513 may actually run more slowly in rare cases):
3515 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3516 png_uint_32 mask, flags;
3518 flags = png_get_asm_flags(png_ptr);
3519 mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
3520 png_set_asm_flags(png_ptr, flags | mask);
3523 To enable only optimizations relevant to reading PNGs, use PNG_SELECT_READ
3524 by itself when calling png_get_asm_flagmask(); similarly for optimizing
3525 only writing. To disable all optimizations:
3527 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3528 flags = png_get_asm_flags(png_ptr);
3529 mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
3530 png_set_asm_flags(png_ptr, flags & ~mask);
3533 To enable or disable only MMX-related features, use png_get_mmx_flagmask()
3534 in place of png_get_asm_flagmask(). The mmx version takes one additional
3537 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3538 int selection = PNG_SELECT_READ | PNG_SELECT_WRITE;
3541 mask = png_get_mmx_flagmask(selection, &compilerID);
3544 On return, compilerID will indicate which version of the MMX assembler
3545 optimizations was compiled. Currently two flavors exist: Microsoft
3546 Visual C++ (compilerID == 1) and GNU C (a.k.a. gcc/gas, compilerID == 2).
3547 On non-x86 platforms or on systems compiled without MMX optimizations, a
3548 value of -1 is used.
3550 Note that both png_get_asm_flagmask() and png_get_mmx_flagmask() return
3551 all valid, settable optimization bits for the version of the library that's
3552 currently in use. In the case of shared (dynamically linked) libraries,
3553 this may include optimizations that did not exist at the time the code was
3554 written and compiled. It is also possible, of course, to enable only known,
3555 specific optimizations; for example:
3557 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3558 flags = PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
3559 | PNG_ASM_FLAG_MMX_READ_INTERLACE \
3560 | PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
3561 | PNG_ASM_FLAG_MMX_READ_FILTER_UP \
3562 | PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
3563 | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH ;
3564 png_set_asm_flags(png_ptr, flags);
3567 This method would enable only the MMX read-optimizations available at the
3568 time of libpng 1.2.0's release, regardless of whether a later version of
3569 the DLL were actually being used. (Also note that these functions did not
3570 exist in versions older than 1.2.0, so any attempt to run a dynamically
3571 linked app on such an older version would fail.)
3573 To determine whether the processor supports MMX instructions at all, use
3574 the png_mmx_support() function:
3576 #if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
3577 mmxsupport = png_mmx_support();
3580 It returns -1 if MMX support is not compiled into libpng, 0 if MMX code
3581 is compiled but MMX is not supported by the processor, or 1 if MMX support
3582 is fully available. Note that png_mmx_support(), png_get_mmx_flagmask(),
3583 and png_get_asm_flagmask() all may be called without allocating and ini-
3584 tializing any PNG structures (for example, as part of a usage screen or
3587 The following code can be used to prevent an application from using the
3588 thread_unsafe features, even if libpng was built with PNG_THREAD_UNSAFE_OK
3591 #if defined(PNG_USE_PNGGCCRD) && defined(PNG_ASSEMBLER_CODE_SUPPORTED) \
3592 && defined(PNG_THREAD_UNSAFE_OK)
3593 /* Disable thread-unsafe features of pnggccrd */
3594 if (png_access_version() >= 10200)
3596 png_uint_32 mmx_disable_mask = 0;
3597 png_uint_32 asm_flags;
3599 mmx_disable_mask |= ( PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
3600 | PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
3601 | PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
3602 | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH );
3603 asm_flags = png_get_asm_flags(png_ptr);
3604 png_set_asm_flags(png_ptr, asm_flags & ~mmx_disable_mask);
3608 For more extensive examples of runtime querying, enabling and disabling
3609 of optimized features, see contrib/gregbook/readpng2.c in the libpng
3610 source-code distribution.
3612 .SH VII. MNG support
3614 The MNG specification (available at http://www.libpng.org/pub/mng) allows
3615 certain extensions to PNG for PNG images that are embedded in MNG datastreams.
3616 Libpng can support some of these extensions. To enable them, use the
3617 png_permit_mng_features() function:
3619 feature_set = png_permit_mng_features(png_ptr, mask)
3620 mask is a png_uint_32 containing the logical OR of the
3621 features you want to enable. These include
3622 PNG_FLAG_MNG_EMPTY_PLTE
3623 PNG_FLAG_MNG_FILTER_64
3624 PNG_ALL_MNG_FEATURES
3625 feature_set is a png_uint_32 that is the logical AND of
3626 your mask with the set of MNG features that is
3627 supported by the version of libpng that you are using.
3629 It is an error to use this function when reading or writing a standalone
3630 PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
3631 in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
3632 and the MHDR and MEND chunks. Libpng does not provide support for these
3633 or any other MNG chunks; your application must provide its own support for
3634 them. You may wish to consider using libmng (available at
3635 http://www.libmng.com) instead.
3637 .SH VIII. Changes to Libpng from version 0.88
3639 It should be noted that versions of libpng later than 0.96 are not
3640 distributed by the original libpng author, Guy Schalnat, nor by
3641 Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
3642 distributed versions 0.89 through 0.96, but rather by another member
3643 of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
3644 still alive and well, but they have moved on to other things.
3646 The old libpng functions png_read_init(), png_write_init(),
3647 png_info_init(), png_read_destroy(), and png_write_destroy() have been
3648 moved to PNG_INTERNAL in version 0.95 to discourage their use. These
3649 functions will be removed from libpng version 2.0.0.
3651 The preferred method of creating and initializing the libpng structures is
3652 via the png_create_read_struct(), png_create_write_struct(), and
3653 png_create_info_struct() because they isolate the size of the structures
3654 from the application, allow version error checking, and also allow the
3655 use of custom error handling routines during the initialization, which
3656 the old functions do not. The functions png_read_destroy() and
3657 png_write_destroy() do not actually free the memory that libpng
3658 allocated for these structs, but just reset the data structures, so they
3659 can be used instead of png_destroy_read_struct() and
3660 png_destroy_write_struct() if you feel there is too much system overhead
3661 allocating and freeing the png_struct for each image read.
3663 Setting the error callbacks via png_set_message_fn() before
3664 png_read_init() as was suggested in libpng-0.88 is no longer supported
3665 because this caused applications that do not use custom error functions
3666 to fail if the png_ptr was not initialized to zero. It is still possible
3667 to set the error callbacks AFTER png_read_init(), or to change them with
3668 png_set_error_fn(), which is essentially the same function, but with a new
3669 name to force compilation errors with applications that try to use the old
3672 Starting with version 1.0.7, you can find out which version of the library
3673 you are using at run-time:
3675 png_uint_32 libpng_vn = png_access_version_number();
3677 The number libpng_vn is constructed from the major version, minor
3678 version with leading zero, and release number with leading zero,
3679 (e.g., libpng_vn for version 1.0.7 is 10007).
3681 You can also check which version of png.h you used when compiling your
3684 png_uint_32 application_vn = PNG_LIBPNG_VER;
3686 .SH IX. Y2K Compliance in libpng
3690 Since the PNG Development group is an ad-hoc body, we can't make
3691 an official declaration.
3693 This is your unofficial assurance that libpng from version 0.71 and
3694 upward through 1.2.8 are Y2K compliant. It is my belief that earlier
3695 versions were also Y2K compliant.
3697 Libpng only has three year fields. One is a 2-byte unsigned integer that
3698 will hold years up to 65535. The other two hold the date in text
3699 format, and will hold years up to 9999.
3702 "png_uint_16 year" in png_time_struct.
3705 "png_charp time_buffer" in png_struct and
3706 "near_time_buffer", which is a local character string in png.c.
3708 There are seven time-related functions:
3710 png_convert_to_rfc_1123() in png.c
3711 (formerly png_convert_to_rfc_1152() in error)
3712 png_convert_from_struct_tm() in pngwrite.c, called
3714 png_convert_from_time_t() in pngwrite.c
3715 png_get_tIME() in pngget.c
3716 png_handle_tIME() in pngrutil.c, called in pngread.c
3717 png_set_tIME() in pngset.c
3718 png_write_tIME() in pngwutil.c, called in pngwrite.c
3720 All appear to handle dates properly in a Y2K environment. The
3721 png_convert_from_time_t() function calls gmtime() to convert from system
3722 clock time, which returns (year - 1900), which we properly convert to
3723 the full 4-digit year. There is a possibility that applications using
3724 libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
3725 function, or that they are incorrectly passing only a 2-digit year
3726 instead of "year - 1900" into the png_convert_from_struct_tm() function,
3727 but this is not under our control. The libpng documentation has always
3728 stated that it works with 4-digit years, and the APIs have been
3731 The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
3732 integer to hold the year, and can hold years as large as 65535.
3734 zlib, upon which libpng depends, is also Y2K compliant. It contains
3735 no date-related code.
3738 Glenn Randers-Pehrson
3740 PNG Development Group
3744 Note about libpng version numbers:
3746 Due to various miscommunications, unforeseen code incompatibilities
3747 and occasional factors outside the authors' control, version numbering
3748 on the library has not always been consistent and straightforward.
3749 The following table summarizes matters since version 0.89c, which was
3750 the first widely used release:
3752 source png.h png.h shared-lib
3753 version string int version
3754 ------- ------ ----- ----------
3755 0.89c ("beta 3") 0.89 89 1.0.89
3756 0.90 ("beta 4") 0.90 90 0.90
3757 0.95 ("beta 5") 0.95 95 0.95
3758 0.96 ("beta 6") 0.96 96 0.96
3759 0.97b ("beta 7") 1.00.97 97 1.0.1
3760 0.97c 0.97 97 2.0.97
3763 0.99a-m 0.99 99 2.0.99
3765 1.0.0 1.0.0 100 2.1.0
3766 1.0.0 (from here on, the 100 2.1.0
3767 1.0.1 png.h string is 10001 2.1.0
3768 1.0.1a-e identical to the 10002 from here on, the
3769 1.0.2 source version) 10002 shared library is 2.V
3770 1.0.2a-b 10003 where V is the source
3771 1.0.1 10001 code version except as
3772 1.0.1a-e 10002 2.1.0.1a-e noted.
3774 1.0.2a-b 10003 2.1.0.2a-b
3776 1.0.3a-d 10004 2.1.0.3a-d
3778 1.0.4a-f 10005 2.1.0.4a-f
3779 1.0.5 (+ 2 patches) 10005 2.1.0.5
3780 1.0.5a-d 10006 2.1.0.5a-d
3781 1.0.5e-r 10100 2.1.0.5e-r
3782 1.0.5s-v 10006 2.1.0.5s-v
3783 1.0.6 (+ 3 patches) 10006 2.1.0.6
3784 1.0.6d-g 10007 2.1.0.6d-g
3787 1.0.6j 10007 2.1.0.6j
3788 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
3789 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
3790 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
3791 1.0.7 1 10007 2.1.0.7
3792 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
3793 1.0.8rc1 1 10008 2.1.0.8rc1
3794 1.0.8 1 10008 2.1.0.8
3795 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
3796 1.0.9rc1 1 10009 2.1.0.9rc1
3797 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
3798 1.0.9rc2 1 10009 2.1.0.9rc2
3799 1.0.9 1 10009 2.1.0.9
3800 1.0.10beta1 1 10010 2.1.0.10beta1
3801 1.0.10rc1 1 10010 2.1.0.10rc1
3802 1.0.10 1 10010 2.1.0.10
3803 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
3804 1.0.11rc1 1 10011 2.1.0.11rc1
3805 1.0.11 1 10011 2.1.0.11
3806 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
3807 1.0.12rc1 2 10012 2.1.0.12rc1
3808 1.0.12 2 10012 2.1.0.12
3809 1.1.0a-f - 10100 2.1.1.0a-f abandoned
3810 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
3811 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
3812 1.2.0rc1 3 10200 3.1.2.0rc1
3813 1.2.0 3 10200 3.1.2.0
3814 1.2.1beta-4 3 10201 3.1.2.1beta1-4
3815 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
3816 1.2.1 3 10201 3.1.2.1
3817 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
3818 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
3819 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
3820 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
3821 1.0.13 10 10013 10.so.0.1.0.13
3822 1.2.2 12 10202 12.so.0.1.2.2
3823 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
3824 1.2.3 12 10203 12.so.0.1.2.3
3825 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
3826 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
3827 1.0.14 10 10014 10.so.0.1.0.14
3828 1.2.4 13 10204 12.so.0.1.2.4
3829 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
3830 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
3831 1.0.15 10 10015 10.so.0.1.0.15
3832 1.2.5 13 10205 12.so.0.1.2.5
3833 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
3834 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
3835 1.0.16 10 10016 10.so.0.1.0.16
3836 1.2.6 13 10206 12.so.0.1.2.6
3837 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
3838 1.0.17rc1 10 10017 12.so.0.1.0.17rc1
3839 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
3840 1.0.17 10 10017 12.so.0.1.0.17
3841 1.2.7 13 10207 12.so.0.1.2.7
3842 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
3843 1.0.18rc1-5 10 10018 12.so.0.1.0.18rc1-5
3844 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
3845 1.0.18 10 10018 12.so.0.1.0.18
3846 1.2.8 13 10208 12.so.0.1.2.8
3848 Henceforth the source version will match the shared-library minor
3849 and patch numbers; the shared-library major version number will be
3850 used for changes in backward compatibility, as it is intended. The
3851 PNG_PNGLIB_VER macro, which is not used within libpng but is available
3852 for applications, is an unsigned integer of the form xyyzz corresponding
3853 to the source version x.y.z (leading zeros in y and z). Beta versions
3854 were given the previous public release number plus a letter, until
3855 version 1.0.6j; from then on they were given the upcoming public
3856 release number plus "betaNN" or "rcN".
3863 http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
3864 http://www.libpng.org/pub/png
3869 (generally) at the same location as
3873 ftp://ftp.info-zip.org/pub/infozip/zlib
3876 .IR PNG specification: RFC 2083
3878 (generally) at the same location as
3882 ftp://ds.internic.net/rfc/rfc2083.txt
3884 or (as a W3C Recommendation) at
3886 http://www.w3.org/TR/REC-png.html
3889 In the case of any inconsistency between the PNG specification
3890 and this library, the specification takes precedence.
3893 This man page: Glenn Randers-Pehrson
3894 <glennrp at users.sourceforge.net>
3896 The contributing authors would like to thank all those who helped
3897 with testing, bug fixes, and patience. This wouldn't have been
3898 possible without all of you.
3900 Thanks to Frank J. T. Wojcik for helping with the documentation.
3902 Libpng version 1.2.8 - December 3, 2004:
3903 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
3904 Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
3906 Supported by the PNG development group
3908 png-implement at ccrc.wustl.edu (subscription required; write to
3909 majordomo at ccrc.wustl.edu with "subscribe png-implement" in the message).
3911 .SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
3913 (This copy of the libpng notices is provided for your convenience. In case of
3914 any discrepancy between this copy and the notices in the file png.h that is
3915 included in the libpng distribution, the latter shall prevail.)
3917 If you modify libpng you may insert additional notices immediately following
3920 libpng version 1.2.6, December 3, 2004, is
3921 Copyright (c) 2004 Glenn Randers-Pehrson, and is
3922 distributed according to the same disclaimer and license as libpng-1.2.5
3923 with the following individual added to the list of Contributing Authors
3927 libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
3928 Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
3929 distributed according to the same disclaimer and license as libpng-1.0.6
3930 with the following individuals added to the list of Contributing Authors
3932 Simon-Pierre Cadieux
3936 and with the following additions to the disclaimer:
3938 There is no warranty against interference with your
3939 enjoyment of the library or against infringement.
3940 There is no warranty that our efforts or the library
3941 will fulfill any of your particular purposes or needs.
3942 This library is provided with all faults, and the entire
3943 risk of satisfactory quality, performance, accuracy, and
3944 effort is with the user.
3946 libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
3947 Copyright (c) 1998, 1999 Glenn Randers-Pehrson
3948 Distributed according to the same disclaimer and license as libpng-0.96,
3949 with the following individuals added to the list of Contributing Authors:
3952 Glenn Randers-Pehrson
3955 libpng versions 0.89, June 1996, through 0.96, May 1997, are
3956 Copyright (c) 1996, 1997 Andreas Dilger
3957 Distributed according to the same disclaimer and license as libpng-0.88,
3958 with the following individuals added to the list of Contributing Authors:
3967 libpng versions 0.5, May 1995, through 0.88, January 1996, are
3968 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
3970 For the purposes of this copyright and license, "Contributing Authors"
3971 is defined as the following set of individuals:
3979 The PNG Reference Library is supplied "AS IS". The Contributing Authors
3980 and Group 42, Inc. disclaim all warranties, expressed or implied,
3981 including, without limitation, the warranties of merchantability and of
3982 fitness for any purpose. The Contributing Authors and Group 42, Inc.
3983 assume no liability for direct, indirect, incidental, special, exemplary,
3984 or consequential damages, which may result from the use of the PNG
3985 Reference Library, even if advised of the possibility of such damage.
3987 Permission is hereby granted to use, copy, modify, and distribute this
3988 source code, or portions hereof, for any purpose, without fee, subject
3989 to the following restrictions:
3991 1. The origin of this source code must not be misrepresented.
3993 2. Altered versions must be plainly marked as such and
3994 must not be misrepresented as being the original source.
3996 3. This Copyright notice may not be removed or altered from
3997 any source or altered source distribution.
3999 The Contributing Authors and Group 42, Inc. specifically permit, without
4000 fee, and encourage the use of this source code as a component to
4001 supporting the PNG file format in commercial products. If you use this
4002 source code in a product, acknowledgment is not required but would be
4006 A "png_get_copyright" function is available, for convenient use in "about"
4009 printf("%s",png_get_copyright(NULL));
4011 Also, the PNG logo (in PNG format, of course) is supplied in the
4012 files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
4014 Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
4015 certification mark of the Open Source Initiative.
4017 Glenn Randers-Pehrson
4018 glennrp at users.sourceforge.net
git://git.onelab.eu / bootcd.git / blob