Grafika\Gd\Filter\Sobel::getColor PHP Method

    private function getColor($gd, &$pixels, $x, $y)
    {
        if (isset($pixels[$x][$y])) {
            return $pixels[$x][$y];
        }
        $color = imagecolorat($gd, $x, $y);
        $r = $color >> 16 & 0xff;
        $g = $color >> 8 & 0xff;
        $b = $color & 0xff;
        return $pixels[$x][$y] = round($r * 0.3 + $g * 0.59 + $b * 0.11);
        // gray
    }