I knew that IM could do it... it's just such a big program things are hard to find and make work. Anyways, this gives output similar to BrowserUk's GD script.

This is only quickly tested, I may have the shift order wrong, etc. The color count dosn't seem to agree with GD. Please test yourself to verify worthiness.

#!/usr/bin/perl
use warnings;
use strict;
use Image::Magick;

my $file = shift or die "Need a file $!\n";

my $img = Image::Magick->new;
$img->ReadImage($file);

$img->Quantize( colors => 18 );
$img->Set( type => 'Palette' );
#$img->Write("$0.png");

# if you want a pixel by pixel list of every color
# a huge slow output
#$img->Set(magick => 'txt');
#$img->Write("$0.txt");

#histogram
#returned values are an array of 
#red, green, blue, opacity, and count values.

my $tot = 0;
my (@colors) = $img->Histogram();

#print join "\n\n", @colors;
# probably some array slice would be better than multi-shifts,
# any code improvement's welcome
while (1){
     if (scalar @colors == 0){last}
     my $r = shift @colors;
     my $g = shift @colors;
     my $b = shift @colors;
     my $o = shift @colors;
     my $count = shift @colors; 
     $tot++;
print "$count ($r,$g,$b) at $o opacity\n"; 
}

print "\n$tot total colors\n";
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