public function getLuminance($red, $green, $blue)
    {
        switch ($this->luminanceStrategy) {
            case 1:
                $luminance = ($red * 0.2126 + $green * 0.7152 + $blue * 0.0722) / 255;
                break;
            case 2:
                $luminance = ($red * 0.299 + $green * 0.587 + $blue * 0.114) / 255;
                break;
            case 3:
                $luminance = sqrt(0.299 * pow($red, 2) + 0.587 * pow($green, 2) + 0.114 * pow($blue, 2)) / 255;
                break;
            case 0:
            default:
                $luminance = ($red + $green + $blue) / (255 * 3);
        }

        return $luminance;
    }