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Forked from niw/libpng_test.c
Last active August 29, 2015 14:21
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/*
* A simple libpng example program
* http://zarb.org/~gc/html/libpng.html
*
* Modified by Yoshimasa Niwa to make it much simpler
* and support all defined color_type.
*
* To build, use the next instruction on OS X.
* $ brew install libpng
* $ clang -lz -lpng15 libpng_test.c
*
* Copyright 2002-2010 Guillaume Cottenceau.
*
* This software may be freely redistributed under the terms
* of the X11 license.
*
*/
#include <stdlib.h>
#include <stdio.h>
#include <png.h>
int width, height;
png_byte color_type;
png_byte bit_depth;
png_bytep *row_pointers;
void read_png_file(char *filename) {
FILE *fp = fopen(filename, "rb");
png_structp png = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
if(!png) abort();
png_infop info = png_create_info_struct(png);
if(!info) abort();
if(setjmp(png_jmpbuf(png))) abort();
png_init_io(png, fp);
png_read_info(png, info);
width = png_get_image_width(png, info);
height = png_get_image_height(png, info);
color_type = png_get_color_type(png, info);
bit_depth = png_get_bit_depth(png, info);
// Read any color_type into 8bit depth, RGBA format.
// See http://www.libpng.org/pub/png/libpng-manual.txt
if(bit_depth == 16)
png_set_strip_16(png);
if(color_type == PNG_COLOR_TYPE_PALETTE)
png_set_palette_to_rgb(png);
// PNG_COLOR_TYPE_GRAY_ALPHA is always 8 or 16bit depth.
if(color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
png_set_expand_gray_1_2_4_to_8(png);
if(png_get_valid(png, info, PNG_INFO_tRNS))
png_set_tRNS_to_alpha(png);
// These color_type don't have an alpha channel then fill it with 0xff.
if(color_type == PNG_COLOR_TYPE_RGB ||
color_type == PNG_COLOR_TYPE_GRAY ||
color_type == PNG_COLOR_TYPE_PALETTE)
png_set_filler(png, 0xFF, PNG_FILLER_AFTER);
if(color_type == PNG_COLOR_TYPE_GRAY ||
color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
png_set_gray_to_rgb(png);
png_read_update_info(png, info);
row_pointers = (png_bytep*)malloc(sizeof(png_bytep) * height);
for(int y = 0; y < height; y++) {
row_pointers[y] = (png_byte*)malloc(png_get_rowbytes(png,info));
}
png_read_image(png, row_pointers);
fclose(fp);
}
void write_png_file(char *filename) {
int y;
FILE *fp = fopen(filename, "wb");
if(!fp) abort();
png_structp png = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
if (!png) abort();
png_infop info = png_create_info_struct(png);
if (!info) abort();
if (setjmp(png_jmpbuf(png))) abort();
png_init_io(png, fp);
// Output is 8bit depth, RGBA format.
png_set_IHDR(
png,
info,
width, height,
8,
PNG_COLOR_TYPE_RGBA,
PNG_INTERLACE_NONE,
PNG_COMPRESSION_TYPE_DEFAULT,
PNG_FILTER_TYPE_DEFAULT
);
png_write_info(png, info);
// To remove the alpha channel for PNG_COLOR_TYPE_RGB format,
// Use png_set_filler().
//png_set_filler(png, 0, PNG_FILLER_AFTER);
png_write_image(png, row_pointers);
png_write_end(png, NULL);
for(int y = 0; y < height; y++) {
free(row_pointers[y]);
}
free(row_pointers);
fclose(fp);
}
void process_png_file() {
for(int y = 0; y < height; y++) {
png_bytep row = row_pointers[y];
for(int x = 0; x < width; x++) {
png_bytep px = &(row[x * 4]);
// Do something awesome for each pixel here...
//printf("%4d, %4d = RGBA(%3d, %3d, %3d, %3d)\n", x, y, px[0], px[1], px[2], px[3]);
}
}
}
int main(int argc, char *argv[]) {
if(argc != 3) abort();
read_png_file(argv[1]);
process_png_file();
write_png_file(argv[2]);
return 0;
}
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