title: Rails json output carrierwave thumbnail version
body: <p>I need to render out a <strong>json</strong> output from a controller and I'd like to include the thumbnail version of my images in the json. </p>
  
  <p>If I render json using only <code>:image_url</code> it outputs the full image url, if I use <code>:image</code> then it will lists all the available images (including thumbnail).</p>
  
  <p>How do I render out in json just the thumbnail version of the image?</p>
  
  <p>Thanks,</p>