This works faster:
use GD;
$img = new GD::Image(400,400);
$blue = $img->colorAllocateAlpha(10,255,60,45);
$black = $img->colorAllocate(0,0,0);
$c = -0.70;
$i = -0.38;
for($x=-200;$x<200;$x++){
for($y=-200;$y<200;$y++){
$rx = $x/100;
$ry = $y/100;
$teller = 0;
lab:
$a = $rx**2 + (($ry**2)*-1) +$c;
$b = (2*$rx*$ry)+$i;
$abs = sqrt($a**2 + $b**2);
if($abs>2){
$img->setPixel(200+$x,200+$y,$black);}
else{
if($teller<20){
$teller++;
$rx = $a;
$ry = $b;
goto lab;
}
}
}
}
binmode STDOUT;
print $img->png;