use GD;
$image = GD::Image->new($filename);
$index = $image->getPixel(20,100);
($r,$g,$b) = $myImage->rgb($index);
[download]

There are many image processing modules - the three major ones are Image::Magick, Imager and GD - any one of the three should do what you want. None of the three are convenient to build, as all three rely on lots and lots of external libraries to do the heavy lifting.

You can definitely do it with ImageMagick/PerlMagick, I've done it myself ages ago -- with a function called getPixel(x,y) which returns an RGB value, if I remember correctly.

---




($_='kkvvttuu bbooppuuiiffss qqffssmm iibbddllffss')
=~y~b-v~a-z~s; print

I have used GD quite extensively on solutions for the http://www.pythonchallenge.com/ puzzles. It allows for you to getPixel($x,$y) and setPixel($x,$y,$color) if needed. The only drawback is that I have even had difficulty installing this module from the PPM on win32. I never seems to have the same issue twice.

Thank you,
Greg W

#!/usr/bin/perl
#None of these is fast, mainly because of the overhead of calling Perl
#code for each pixel.
use strict;

my $imagefile = shift or die "No file specified\n";

sub rgba2hex {
    sprintf "%02x%02x%02x%02x", map { $_ || 0 } @_;
}

{
    use Imager;
    my %colors;
    my $img = Imager->new();
    $img->open( file => $imagefile ) or die $img->errstr;
    my ( $w, $h ) = ( $img->getwidth, $img->getheight );
    for my $i ( 0 .. $w - 1 ) {
        for my $j ( 0 .. $h - 1 ) {
            my $color = $img->getpixel( x => $i, y => $j );
            my $hcolor = rgba2hex $color->rgba();
            print "$hcolor ";
        $colors{$hcolor}++;
        }
    }

    printf "Imager: Number of colours: %d\n", scalar keys %colors;
}

{
    use GD;
    my %colors;
    my $gd = GD::Image->new($imagefile) or die "GD::Image->new($imagef
+ile)";
    my ( $w, $h ) = $gd->getBounds();
    for my $i ( 0 .. $w - 1 ) {
        for my $j ( 0 .. $h - 1 ) {
            my $index = $gd->getPixel( $i, $j );
            my $hcolor = rgba2hex( $gd->rgb($index), 0 );
            $colors{$hcolor}++;
        }
    }

    printf "GD: Number of colours: %d\n", scalar keys %colors;
}

{
    use Image::Magick;
    my %colors;
    my $img = Image::Magick->new();
    my $rc  = $img->Read($imagefile);
    die $rc if $rc;
    my ( $w, $h ) = $img->Get( 'width', 'height' );
    for my $i ( 0 .. $w - 1 ) {
        for my $j ( 0 .. $h - 1 ) {
            my $color = $img->Get("pixel[$i,$j]");
            my $hcolor = rgba2hex split /,/, $color;
            $colors{$hcolor}++;
        }
    }

    printf "Image::Magick: Number of colours: %d\n", scalar keys %colo
+rs;
}
[download]