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

    private function convolve($matrix)
    {
        $gx = $matrix[0][0] + $matrix[2][0] * -1 + $matrix[0][1] * 2 + $matrix[2][1] * -2 + $matrix[0][2] + $matrix[2][2] * -1;
        $gy = $matrix[0][0] + $matrix[1][0] * 2 + $matrix[2][0] + $matrix[0][2] * -1 + $matrix[1][2] * -2 + $matrix[2][2] * -1;
        return sqrt($gx * $gx + $gy * $gy);
    }