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

    private function getColor($px, &$pixels, $x, $y)
    {
        if (isset($pixels[$x][$y])) {
            return $pixels[$x][$y];
        }
        $rgba = $px->getColor();
        return $pixels[$x][$y] = round($rgba['r'] * 0.3 + $rgba['g'] * 0.59 + $rgba['b'] * 0.11);
        // gray
    }