protected function isPreviewDisplayable()
    {
        $image_area = $this->width * $this->height;
        $preview_area = $this->preview_width * $this->preview_height;

        $difference = ($preview_area - $image_area) / $image_area;

        return $this->preview_image != '' &&
            ($this->show_preview_when_smaller || $difference >= 0.2);
    }