ReadWritePng.cpp

/*
 * Copyright 2002-2008 Guillaume Cottenceau.
 *
 * This software may be freely redistributed under the terms
 * of the X11 license.
 *
 */

#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;

png_byte color_type;
png_byte bit_depth;

png_structp png_ptr;
png_infop info_ptr;
int number_of_passes;
png_bytep * row_pointers;
int width, height;

void read_png_file(char* file_name)
{
  png_byte 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 = info_ptr->width;
  height = info_ptr->height;
  color_type = info_ptr->color_type;
  bit_depth = info_ptr->bit_depth;

  number_of_passes = png_set_interlace_handling(png_ptr);
  png_read_update_info(png_ptr, info_ptr);

  printf("%d %d %d %d\n",width,height,color_type,bit_depth);
  /* read file */
  if (setjmp(png_jmpbuf(png_ptr)))
    abort_("[read_png_file] Error during read_image");

  row_pointers = (png_bytep*) malloc(sizeof(png_bytep) * height);
  for (y=0; y<height; y++)
    row_pointers[y] = (png_byte*) malloc(info_ptr->rowbytes);

  png_read_image(png_ptr, row_pointers);

  fclose(fp);
}


void write_png_file(char* file_name,png_bytep * row_pointers,int ImWidth,int ImHeight)
{
  /* create file */
  FILE *fp = fopen(file_name, "wb");
  if (!fp)
    abort_("[write_png_file] File %s could not be opened for writing", file_name);


  /* initialize stuff */
  png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
   
  if (!png_ptr)
    abort_("[write_png_file] png_create_write_struct failed");

  info_ptr = png_create_info_struct(png_ptr);
  if (!info_ptr)
    abort_("[write_png_file] png_create_info_struct failed");

  if (setjmp(png_jmpbuf(png_ptr)))
    abort_("[write_png_file] Error during init_io");

  png_init_io(png_ptr, fp);


  /* write header */
  if (setjmp(png_jmpbuf(png_ptr)))
    abort_("[write_png_file] Error during writing header");

  png_set_IHDR(png_ptr, info_ptr, ImWidth, ImHeight,
          bit_depth, color_type, PNG_INTERLACE_NONE,
          PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);

  png_write_info(png_ptr, info_ptr);


  /* write bytes */
  if (setjmp(png_jmpbuf(png_ptr)))
    abort_("[write_png_file] Error during writing bytes");

  png_write_image(png_ptr, row_pointers);


  /* end write */
  if (setjmp(png_jmpbuf(png_ptr)))
    abort_("[write_png_file] Error during end of write");

  png_write_end(png_ptr, NULL);

  /* cleanup heap allocation */
  for (y=0; y<ImHeight; y++)
    free(row_pointers[y]);
  free(row_pointers);

  fclose(fp);
}


void process_file(int height,int width)
{
  if (info_ptr->color_type != PNG_COLOR_TYPE_RGBA)
    abort_("[process_file] color_type of input file must be PNG_COLOR_TYPE_RGBA (is %d)", info_ptr->color_type);

  for (y=0; y<height; y++) {
    png_byte* row = row_pointers[y];
    for (x=0; x<width; x++) {
      png_byte* ptr = &(row[x*4]);
      //printf("Pixel at position [ %d - %d ] has the following RGBA values: %d - %d - %d - %d\n",x, y, ptr[0], ptr[1], ptr[2], ptr[3]);

      /* set red value to 0 and green value to the blue one */
      ptr[0] = 0;
      ptr[1] = ptr[2];
    }
  }

}


int main(int argc, char **argv)
{
  if (argc != 3)
    abort_("Usage: program_name <file_in> <file_out>");

  read_png_file(argv[1]);
  process_file(width,height);
  write_png_file(argv[2],row_pointers,width,height);

  return 0;
}