use GD;

sub getindex {
    my $image = shift;
    my $index = $image->colorExact(@_);
    $index == -1 ?
       $image->colorAllocate(@_) :
            $index;
}

##</code><code>##

my $reference_image = new GD::Image(100,100);
my @colornames;
{
    my $goodline = qr/^\d/;
    open my $rgbdat, '<', '/usr/X11/lib/X11/rgb.txt'
            or die $!;
    while (<$rgbdat>) {
        /$goodline/ or next;
        my @dat = split " ", $_, 4;
        my $color = pop @dat;
        $colornames[getindex($reference_image, @dat)] = $color;
    }
    close $rgbdat or die $!;
}

##</code><code>##

my $image = GD::Image->newFromJpeg('many.jpg') or die $!;
my @size = $image->Bounds();

##</code><code>##

my $new_image = GD::Image->new @size;


##</code><code>##

{
    my ($ix, $iy, @rgb);     # preallocate and reuse
    for $ix (0 .. $size[0]-1) {
        for $iy (0 .. $size[1]-1) {
            @rgb = $image->rgb(image->getPixel($ix,$iy)));
            @rgb = $reference_image->rgb( $reference_image->colorClosestHWB( @rgb ));
            $new_image->setPixel($ix, $iy, getindex($new_image, @rgb));
        }
    }
}

##</code><code>##

sub getcolor {
    return "puke" unless @_ == 3;
    $colornames[$reference_image->colorClosestHWB(@_)]
}