public function resize($filename, $width, $height)
    {
        // open an image file
        $img = Image::make($this->pathOfImagesUploadFolder() .'/'. $filename);

        // resize image
        // http://image.intervention.io/api/resize
        // closure prevents possible upsizing
        $img->resize($width, $height, function ($constraint) {
            $constraint->aspectRatio();
            $constraint->upsize();
        });

        $img->save($this->pathFilenameOfResizedImage($filename, $width, $height));
    }