$RED = 255;
  $GREEN = 0;
  $BLUE = 0;

  open STDOUT, "| ppmtogif" or die "open: $!";
  # "1 1" means that the image is 1x1 pixel.
  # "255" means that 255 is the maximum color intensity.
  print "P3 1 1 255 $RED $GREEN $BLUE\n";
  close STDOUT or die "close: $!";