Extracting RAW Image Data from PNG

ReadMe.md

#Exporting RAW Image Data from PNG files with libpng

This is an Xcode project which uses libpng to export the raw image data from a png file.

Usage:

pngdump source.png destination.dat

This Xcode project links against libpng. On OS X that's available via homebrew

main.m

//
//  main.m
//  pngdump
//
//  Created by Johnnie Walker on 17/04/2014.
//  Copyright (c) 2014 LateNiteSoft. All rights reserved.
//

#import <Foundation/Foundation.h>

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdarg.h>

#define PNG_DEBUG 3
#include <png.h>

void abort_(const char * s, ...)
{
    va_list args;
    va_start(args, s);
    vfprintf(stderr, s, args);
    fprintf(stderr, "\n");
    va_end(args);
    abort();
}

int x, y;

int width, height;
png_byte color_type;
png_byte bit_depth;

png_structp png_ptr;
png_infop info_ptr;
int number_of_passes;
png_bytep * row_pointers;
size_t data_length;

// thank you @gcotenc http://zarb.org/~gc/html/libpng.html
void read_png_file(const char* file_name)
{
    png_const_bytep header[8];    // 8 is the maximum size that can be checked
    
    /* open file and test for it being a png */
    FILE *fp = fopen(file_name, "rb");
    if (!fp)
        abort_("[read_png_file] File %s could not be opened for reading", file_name);
    fread(header, 1, 8, fp);
    if (png_sig_cmp(header, 0, 8))
        abort_("[read_png_file] File %s is not recognized as a PNG file", file_name);
    
    
    /* initialize stuff */
    png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    
    if (!png_ptr)
        abort_("[read_png_file] png_create_read_struct failed");
    
    info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr)
        abort_("[read_png_file] png_create_info_struct failed");
    
    if (setjmp(png_jmpbuf(png_ptr)))
        abort_("[read_png_file] Error during init_io");
    
    png_init_io(png_ptr, fp);
    png_set_sig_bytes(png_ptr, 8);
    
    png_read_info(png_ptr, info_ptr);
    
    width = png_get_image_width(png_ptr, info_ptr);
    height = png_get_image_height(png_ptr, info_ptr);
    color_type = png_get_color_type(png_ptr, info_ptr);
    bit_depth = png_get_bit_depth(png_ptr, info_ptr);
    
    number_of_passes = png_set_interlace_handling(png_ptr);
    png_read_update_info(png_ptr, info_ptr);
    
    
    /* read file */
    if (setjmp(png_jmpbuf(png_ptr)))
        abort_("[read_png_file] Error during read_image");
    
    png_size_t row_bytes = png_get_rowbytes(png_ptr,info_ptr);
    data_length = row_bytes * height;
    void *data = malloc(data_length);
    
    row_pointers = (png_bytep*) malloc(sizeof(png_bytep) * height);
    for (y=0; y<height; y++) {
        row_pointers[y] = data;
        data += row_bytes;
        // row_pointers[y] = (png_byte*) malloc(png_get_rowbytes(png_ptr,info_ptr));
    }
    
    png_read_image(png_ptr, row_pointers);
    
    fclose(fp);
}


int main(int argc, const char * argv[])
{

    @autoreleasepool {
        const char *input = argv[1];
        const char *output = argv[2];

        read_png_file(input);
        
        NSData *imageData = [NSData dataWithBytesNoCopy:row_pointers[0] length:data_length freeWhenDone:YES];
        [imageData writeToFile:[NSString stringWithCString:output encoding:NSUTF8StringEncoding] atomically:NO];
    }
    return 0;
}

true