#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<time.h>
#include<png.h>

int main(int argc, char **argv)
{
   png_image image;
   png_bytep buffer1, buffer2;
   int s, i;

   if( argc != 4 )
      return printf("%s <input.png> <output1.png> <output2.png>\n", *argv);

   memset(&image, 0, sizeof(image));
   image.version = PNG_IMAGE_VERSION;
   if( !png_image_begin_read_from_file(&image, argv[1]) )
      return printf("Error reading %s\n", argv[1]);

   image.format = PNG_FORMAT_RGBA;
   s = image.width * image.height;
   buffer1 = (png_bytep)malloc(s * 4);
   buffer2 = (png_bytep)calloc(s, 4);
   if( buffer1 == NULL || buffer2 == NULL )
      return puts("Out of memory");
   if( !png_image_finish_read(&image, NULL, buffer1, 0, NULL) )
      return printf("Error loading %s\n", argv[1]);

   srand(time(NULL));
   for(i = 0; i < s; i++)
   {
      if( rand() > RAND_MAX / 2 )
      {
         memcpy(buffer2 + (i * 4), buffer1 + (i * 4), 4);
         memset(buffer1 + (i * 4), 0, 4);
      }
   }

   if( !png_image_write_to_file(&image, argv[2], 0, buffer1, 0, NULL) )
      return printf("Error writing %s\n", argv[2]);
   if( !png_image_write_to_file(&image, argv[3], 0, buffer2, 0, NULL) )
      return printf("Error writing %s\n", argv[3]);

   return 0;
}