title: Twig read image height/width attributes
body: <p>I have an image like so:</p>
  
  <pre><code>{% image output='/images/foo.jpg' '@MyBundle/Resources/public/images/bar.jpg' %}
      &lt;img src="{{ asset(asset_url) }}" alt="Something"&gt;
  {% endimage %}
  </code></pre>
  
  <p>now I would like to get the image dimensions and add width and height attributes like</p>
  
  <pre><code>{% image output='/images/foo.jpg' '@MyBundle/Resources/public/images/bar.jpg' %}
      &lt;img src="{{ asset(asset_url) }}" alt="Something" width="{{ asset(asset_width) }}" height="{{ asset(asset_height) }}"&gt;
  {% endimage %}
  </code></pre>
  
  <p>Is this possible?</p>
  
  <p>Best Regards</p>