When using truecolor images, I've found that I can skip the colorAllocate() step by specifying the packed rgb value inplace of the index. I use

sub rgb{ unpack 'N', pack 'xCCC', @_ }
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for this, though the name is probably a misnomer.

I'm not sure if this is documented anywhere, and cpan seems to be down at the moment, so I haven't been able to check. It seems to work okay with GD v2.30. It's also a lot faster and more convenient than using colorAllocate() to build an rbg->index table.

This is a simpler, faster version of your original that uses the above:

#!/usr/bin/perl -slw
use strict;
use GD;

sub rgb{ unpack 'N', pack 'xCCC', @_ }

my $width = 800;
my $height = 600;
my $img = new GD::Image( $width, $height, 1 );

for my $x ( 0 .. $width -1 ) {
    for my $y ( 0 .. $height -1 ) {
        $img->setPixel( 
            $x, $y, rgb( $x * 255 / $width, $y * 255 / $height, 0 ) 
        );
    }
}

open my $fh, '>:raw', 'picture.png' or die "uh oh spaghettio : $!";
print $fh $img->png;
close $fh;

## display result on win32 systems
system 'picture.png';
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Thank you for the help! This is exactly what I was looking for!

-Alan

Dunno that much about GD, but you can make your code more efficient like so:

use GD;

my $width = 800;
my $height = 600;

my $img = new GD::Image($width,$height,1);

#draw some shizzle
for (my $i=0; $i<=$width; $i++) {

  # calc $i colour only when $i changes
  my $icol = int(($i*255)/$width);

  for (my $j=0; $j<=$height; $j++) {

    # calc colorAllocate here and lose previous loop
    # also, no need to calc 3rd colour param 
    $img->setPixel($i,$j,$img->colorAllocate($icol,int(($j*255)/$heigh
+t),0));
  }
}

#output the picture
open(PICTURE, ">$test.png") or die("uh oh spaghettio");
binmode PICTURE;
print PICTURE $img->png;
close PICTURE;
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<update>wasn't black to red...</update>

<update>...and we don't need @colors anymore...</update>