public function getPixelFormat()
    {
        if ($this->pixelFormat === null) {
            $match = [];
            preg_match(self::$REGEX_PIXEL_FORMAT, $this->output, $match);
            $this->pixelFormat = array_key_exists(1, $match) ? trim($match[1]) : '';
        }

        return $this->pixelFormat;
    }