private function getQuality($quality, $extension) {

		if(false === ('-' . intval($quality) == '-' . $quality)) {
			return trigger_error(sprintf('Argument 1 passed to %s() must be of the type integer, "%s" given', __METHOD__, gettype($quality)), E_USER_ERROR);
		}

		if(false === is_string($extension)) {
			return trigger_error(sprintf('Argument 2 passed to %s() must be of the type string, "%s" given', __METHOD__, gettype($extension)), E_USER_ERROR);
		}

		if(strtolower($extension) === 'png' && $quality > 9) {
			$quality = floor(($quality - 1) / 10);
		}

		return $quality;
	}