<?php
declare(strict_types=1);

$image = imagecreatetruecolor(8, 6);
imagefill($image, 0, 0, imagecolorallocate($image, 20, 40, 60));
imageconvolution($image, [[0,0,0], [0,1,0], [0,0,0]], 1.0, 0.0);
$pixel = imagecolorsforindex($image, imagecolorat($image, 2, 2));
echo $pixel["red"], ",", $pixel["green"], ",", $pixel["blue"], "\n";
