sub score_images { 
	for(my $i = 1; $i <= $population; $i++){ 
		my $flag = 1; 
		for(my $l = 0; $l < @touched; $l++){ 
			if($i == $touched[$l]) { $flag = 0; } 
		} 
		if($flag == 0 || $firstrun == 1){ 
			$score[$i] = 0; 
			${"thr".$i} = new Thread \&pixel_comparison, $i;  
		} 
	} 
	while($runningthreads > 0){	} 
	for(my $i = 1; $i <= $population; $i++){ 
		if($score[$i] < $best){ 
			$best = $score[$i]; 
			$savedIndex = $i; 
		} 
	} 
	@touched = (); 
} 
 
sub pixel_comparison { 
	$runningthreads++; 
	foreach my $x ( 0 .. $width ) { 
			foreach my $y ( 0 .. $height ) { 
				my ($index1) = $timage->getPixel($x,$y); 
				my ($index2) = $im[$_[0]]->getPixel($x,$y); 
				my ($r1,$g1,$b1) = $timage->rgb($index1); 
				my ($r2,$g2,$b2) = $im[$_[0]]->rgb($index2); 
				$score[$_[0]] += ($r1 - $r2)**2; 
				$score[$_[0]] += ($g1 - $g2)**2; 
				$score[$_[0]] += ($b1 - $b2)**2; 
			} 
		} 
	$runningthreads--; 
}

$thread[$i] = Thread->new(\&pixel_comparison, $i);

my $timage :shared; 
my $width :shared; 
my $height :shared; 
my @im :shared; 
my @score :shared;

$timage = GD::Image->newFromPng("ml.png"); 
($width, $height) = $timage->getBounds;

for(my $i = 1; $i <= $population; $i++){ 
		$im[$i] = new GD::Image($width,$height,1); 
... 
...

my ($index1) = $timage->getPixel($x,$y); #My code crashes on this line 
my ($index2) = $im[$_[0]]->getPixel($x,$y);

$poly->addPt(${"xchrom".$i}[$z], ${"ychrom".$i}[$z]); 
$poly->addPt(${"xchrom".$i}[$z+1], ${"ychrom".$i}[$z+1]); 
$poly->addPt(${"xchrom".$i}[$z+2], ${"ychrom".$i}[$z+2]); 
$poly->addPt(${"xchrom".$i}[$z+3], ${"ychrom".$i}[$z+3]);

$poly->addPt($xchrom[$i][$z], $ychrom[$i][$z]);

#!/usr/bin/perl 
use strict; 
use warnings; 
use threads; 
use threads::shared; 
use GD; 
 
my @score :shared; 
my @im; 
my @thr; 
 
$im[0] = GD::Image->newFromPng("img0.png"); 
$im[1] = GD::Image->newFromPng("img1.png"); 
$im[2] = GD::Image->newFromPng("img2.png"); 
 
my ($width, $height) = $im[0]->getBounds; 
 
for(my $i = 1; $i <= 2; $i++){ 
	$thr[$i] = threads->create(\&threaded_sub, $i, $im[0], $im[$i]); 
} 
 
for(my $i = 1; $i <= 2; $i++){ 
	$thr[$i] -> join(); 
	print $score[$i]."\n"; 
} 
 
sub threaded_sub { 
	$score[$_[0]] = 0; 
	foreach my $x ( 0 .. $width ) { 
			foreach my $y ( 0 .. $height ) { 
				my ($index1) = $_[2]->getPixel($x,$y); 
				my ($index2) = $_[1]->getPixel($x,$y); 
				my ($r1,$g1,$b1) = $_[2]->rgb($index1); 
				my ($r2,$g2,$b2) = $_[1]->rgb($index2); 
				$score[$_[0]] += ($r1 - $r2)**2; 
				$score[$_[0]] += ($g1 - $g2)**2; 
				$score[$_[0]] += ($b1 - $b2)**2; 
			} 
	} 
}