public function saveScreenshot($filename = null, $filepath = null)
    {
        // Under Cygwin, uniqid with more_entropy must be set to true.
        // No effect in other environments.
        $filename = $filename ?: sprintf('%s_%s_%s.%s', $this->getMinkParameter('browser_name'), date('c'), uniqid('', true), 'png');
        $filepath = $filepath ?: (ini_get('upload_tmp_dir') ? ini_get('upload_tmp_dir') : sys_get_temp_dir());
        file_put_contents($filepath . '/' . $filename, $this->getSession()->getScreenshot());
    }