diff options
Diffstat (limited to 'example.c')
| -rw-r--r-- | example.c | 120 |
1 files changed, 67 insertions, 53 deletions
@@ -1,36 +1,36 @@ /* example.c - an example of using libpng */ /* This is an example of how to use libpng to read and write PNG files. - The file libpng.txt is much more verbose then this. If you have not - read it, do so first. This was designed to be a starting point of an - implementation. This is not officially part of libpng, and therefore - does not require a copyright notice. - - This file does not currently compile, because it is missing certain - parts, like allocating memory to hold an image. You will have to - supply these parts to get it to compile. For an example of a minimal - working PNG reader/writer, see pngtest.c, included in this distribution. -*/ + * The file libpng.txt is much more verbose then this. If you have not + * read it, do so first. This was designed to be a starting point of an + * implementation. This is not officially part of libpng, and therefore + * does not require a copyright notice. + * + * This file does not currently compile, because it is missing certain + * parts, like allocating memory to hold an image. You will have to + * supply these parts to get it to compile. For an example of a minimal + * working PNG reader/writer, see pngtest.c, included in this distribution. + */ #include <png.h> /* Check to see if a file is a PNG file using png_check_sig(). Returns - non-zero if the image is a PNG, and 0 if it isn't a PNG. - - If this call is successful, and you are going to keep the file open, - you should call png_set_sig_bytes(png_ptr, PNG_BYTES_TO_CHECK); once - you have created the png_ptr, so that libpng knows your application - has read that many bytes from the start of the file. Make sure you - don't call png_set_sig_bytes() with more than 8 bytes read or give it - an incorrect number of bytes read, or you will either have read too - many bytes (your fault), or you are telling libpng to read the wrong - number of magic bytes (also your fault). - - Many applications already read the first 2 or 4 bytes from the start - of the image to determine the file type, so it would be easiest just - to pass the bytes to png_check_sig() or even skip that if you know - you have a PNG file, and call png_set_sig_bytes(). -*/ + * non-zero if the image is a PNG, and 0 if it isn't a PNG. + * + * If this call is successful, and you are going to keep the file open, + * you should call png_set_sig_bytes(png_ptr, PNG_BYTES_TO_CHECK); once + * you have created the png_ptr, so that libpng knows your application + * has read that many bytes from the start of the file. Make sure you + * don't call png_set_sig_bytes() with more than 8 bytes read or give it + * an incorrect number of bytes read, or you will either have read too + * many bytes (your fault), or you are telling libpng to read the wrong + * number of magic bytes (also your fault). + * + * Many applications already read the first 2 or 4 bytes from the start + * of the image to determine the file type, so it would be easiest just + * to pass the bytes to png_check_sig() or even skip that if you know + * you have a PNG file, and call png_set_sig_bytes(). + */ #define PNG_BYTES_TO_CHECK 4 int check_if_png(char *file_name, FILE **fp) { @@ -49,10 +49,11 @@ int check_if_png(char *file_name, FILE **fp) } /* Read a PNG file. You may want to return an error code if the read - fails (depending upon the failure). There are two "prototypes" given - here - one where we are given the filename, and we need to open the - file, and the other where we are given an open file (possibly with - some or all of the magic bytes read - see comments above). */ + * fails (depending upon the failure). There are two "prototypes" given + * here - one where we are given the filename, and we need to open the + * file, and the other where we are given an open file (possibly with + * some or all of the magic bytes read - see comments above). + */ **** prototype 1 **** void read_png(char *file_name) /* We need to open the file */ { @@ -118,7 +119,8 @@ void read_png(FILE *fp, unsigned int sig_read) /* file is already open */ **** PNG file I/O method 2 **** /* If you are using replacement read functions, instead of calling - * png_init_io() here you would call */ + * png_init_io() here you would call: + */ png_set_read_fn(png_ptr, (void *)user_io_ptr, user_read_fn); /* where user_io_ptr is a structure you want available to the callbacks */ **** Use only one I/O method! **** @@ -143,29 +145,31 @@ void read_png(FILE *fp, unsigned int sig_read) /* file is already open */ /* tell libpng to strip 16 bit/color files down to 8 bits/color */ png_set_strip_16(png_ptr); - /* strip alpha bytes from the input data without combining with th - * background (not recommended) */ + /* Strip alpha bytes from the input data without combining with th + * background (not recommended). + */ png_set_strip_alpha(png_ptr); - /* extract multiple pixels with bit depths of 1, 2, and 4 from a single + /* Extract multiple pixels with bit depths of 1, 2, and 4 from a single * byte into separate bytes (useful for paletted and grayscale images). */ png_set_packing(png_ptr); - /* change the order of packed pixels to least significant bit first + /* Change the order of packed pixels to least significant bit first * (not useful if you are using png_set_packing). */ png_set_packswap(png_ptr); - /* expand paletted colors into true RGB triplets */ + /* Expand paletted colors into true RGB triplets */ if (color_type == PNG_COLOR_TYPE_PALETTE) png_set_expand(png_ptr); - /* expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel */ + /* Expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel */ if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8) png_set_expand(png_ptr); - /* expand paletted or RGB images with transparency to full alpha channels - * so the data will be available as RGBA quartets */ + /* Expand paletted or RGB images with transparency to full alpha channels + * so the data will be available as RGBA quartets. + */ if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)) png_set_expand(png_ptr); @@ -207,13 +211,17 @@ void read_png(FILE *fp, unsigned int sig_read) /* file is already open */ * by the user at run time by the user. It is strongly suggested that * your application support gamma correction. */ - if (png_get_gAMA(png_ptr, info_ptr, &image_gamma); - png_set_gamma(png_ptr, screen_gamma, image_gamma); - else - png_set_gamma(png_ptr, screen_gamma, 0.45); + if (png_get_sRGB(png_ptr, info_ptr, &srgb_intent) + png_set_sRGB(png_ptr, srgb_intent, 0); + else + if (png_get_gAMA(png_ptr, info_ptr, &image_gamma) + png_set_gamma(png_ptr, screen_gamma, image_gamma); + else + png_set_gamma(png_ptr, screen_gamma, 0.45); /* Dither RGB files down to 8 bit palette or reduce palettes - to the number of colors available on your screen */ + * to the number of colors available on your screen. + */ if (color_type & PNG_COLOR_MASK_COLOR) { png_uint_32 num_palette; @@ -269,19 +277,19 @@ void read_png(FILE *fp, unsigned int sig_read) /* file is already open */ /* Turn on interlace handling. REQUIRED if you are not using * png_read_image(). To see how to handle interlacing passes, - * see the png_read_row() method below. + * see the png_read_row() method below: */ number_passes = png_set_interlace_handling(png_ptr); - /* optional call to gamma correct and add the background to the palette + /* Optional call to gamma correct and add the background to the palette * and update info structure. REQUIRED if you are expecting libpng to * update the palette for you (ie you selected such a transform above). */ png_read_update_info(png_ptr, info_ptr); - /* allocate the memory to hold the image using the fields of info_ptr. */ + /* Allocate the memory to hold the image using the fields of info_ptr. */ - /* the easiest way to read the image */ + /* The easiest way to read the image: */ png_bytep row_pointers[height]; for (row = 0; row < height; row++) @@ -294,7 +302,7 @@ void read_png(FILE *fp, unsigned int sig_read) /* file is already open */ png_read_image(png_ptr, row_pointers); **** Read the image one or more scanlines at a time **** - /* the other way to read images - deal with interlacing */ + /* The other way to read images - deal with interlacing: */ for (pass = 0; pass < number_passes; pass++) { @@ -552,7 +560,8 @@ void write_png(char *file_name, ... other image information ...) /* Optional gamma chunk is strongly suggested if you have any guess - * as to the correct gamma of the image. */ + * as to the correct gamma of the image. + */ png_set_gAMA(png_ptr, info_ptr, gamma); /* Optionally write comments into the image */ @@ -568,6 +577,8 @@ void write_png(char *file_name, ... other image information ...) png_set_text(png_ptr, info_ptr, text_ptr, 2); /* other optional chunks like cHRM, bKGD, tRNS, tIME, oFFs, pHYs, */ + /* note that if sRGB is present the cHRM chunk must be ignored + * on read and must be written in accordance with the sRGB profile */ /* Write the file header information. REQUIRED */ png_write_info(png_ptr, info_ptr); @@ -579,13 +590,15 @@ void write_png(char *file_name, ... other image information ...) */ /* set up the transformations you want. Note that these are - * all optional. Only call them if you want them. */ + * all optional. Only call them if you want them. + */ /* invert monocrome pixels */ png_set_invert(png_ptr); /* Shift the pixels up to a legal bit depth and fill in - * as appropriate to correctly scale the image */ + * as appropriate to correctly scale the image. + */ png_set_shift(png_ptr, &sig_bit); /* pack pixels into bytes */ @@ -595,7 +608,8 @@ void write_png(char *file_name, ... other image information ...) png_set_swap_alpha(png_ptr); /* Get rid of filler (OR ALPHA) bytes, pack XRGB/RGBX/ARGB/RGBA into - * RGB (4 channels -> 3 channels). The second parameter is not used. */ + * RGB (4 channels -> 3 channels). The second parameter is not used. + */ png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE); /* flip BGR pixels to RGB */ |