int main(void)
{
  const int dimx = 800, dimy = 800;
  int i, j;
  FILE *fp = fopen(, ); 
  (void) fprintf(fp, , dimx, dimy);
  for (j = 0; j < dimy; ++j)
  {
    for (i = 0; i < dimx; ++i)
    {
      static unsigned char color[3];
      color[0] = i % 256;  
      color[1] = j % 256;  
      color[2] = (i * j) % 256;  
      (void) fwrite(color, 1, 3, fp);
    }
  }
  (void) fclose(fp);
  return EXIT_SUCCESS;
}