public function toHSL($red, $green, $blue)
    {
        $min = min($red, $green, $blue);
        $max = max($red, $green, $blue);

        $l = $min + $max;
        $d = $max - $min;

        if ((int) $d === 0) {
            $h = $s = 0;
        } else {
            if ($l < 255) {
                $s = $d / $l;
            } else {
                $s = $d / (510 - $l);
            }

            if ($red == $max) {
                $h = 60 * ($green - $blue) / $d;
            } elseif ($green == $max) {
                $h = 60 * ($blue - $red) / $d + 120;
            } elseif ($blue == $max) {
                $h = 60 * ($red - $green) / $d + 240;
            }
        }

        return [Type::T_HSL, fmod($h, 360), $s * 100, $l / 5.1];
    }