protected function determineOutputFormat($pathToImage)
    {
        $outputFormat = pathinfo($pathToImage, PATHINFO_EXTENSION);

        if ($this->outputFormat != '') {
            $outputFormat = $this->outputFormat;
        }

        $outputFormat = strtolower($outputFormat);

        if (! $this->isValidOutputFormat($outputFormat)) {
            $outputFormat = 'jpg';
        }

        return $outputFormat;
    }