public function colorize($red, $green, $blue, $alpha = 127) {
		$normalizer = function ($value) { return max(-255, min(255, $value)); };
		$red = $normalizer($red);
		$green = $normalizer($green);
		$blue = $normalizer($blue);
		$alpha = min(127, max(0, $alpha));
		imagefilter($this->resource, IMG_FILTER_COLORIZE, $red, $green, $blue, $alpha);
		return $this;
	}