protected function getThumbnailParams($viewMode = null)
    {
        $result = [
            'mode' => 'crop',
            'ext' => 'png'
        ];

        if ($viewMode) {
            if ($viewMode == self::VIEW_MODE_LIST) {
                $result['width'] = 75;
                $result['height'] = 75;
            }
            else {
                $result['width'] = 165;
                $result['height'] = 165;
            }
        }

        return $result;
    }