title: Transparent PNGs don't retain transparency after being transformed (Django + PIL)
body: <p>I'm using <a href="http://thumbnail.sorl.net/" rel="noreferrer">sorl-thumbnail</a>, <a href="http://www.pythonware.com/products/pil/" rel="noreferrer">PIL</a>, and <a href="https://www.djangoproject.com/" rel="noreferrer">Django</a> on a webserver to dynamically create thumbnails in templates.</p>
  
  <p>PIL is installed with PNG support, but for some reason the transformations are creating some really bizarre artifacts on the transparent portions of the images.</p>
  
  <p>I used this gist on Github to install the required dependencies: <a href="https://raw.github.com/gist/1225180/eb87ceaa7277078f17f76a89a066101ba2254391/patch.sh" rel="noreferrer">https://raw.github.com/gist/1225180/eb87ceaa7277078f17f76a89a066101ba2254391/patch.sh</a></p>
  
  <p>Here is the template code that generates the images (I don't think this is where the problem is, but can't hurt to show you):</p>
  
  <pre><code>{% thumbnail project.image "148x108" crop="center" as im %}
    &lt;img src='{{ im.url }}' /&gt;
  {% endthumbnail %}
  </code></pre>
  
  <p>Below is an example of what happens. Any help is greatly appreciated!</p>
  
  <h2>Before</h2>
  
  <p><img src="https://i.stack.imgur.com/dqUOO.png" alt="Image with transparency"></p>
  
  <h2>After</h2>
  
  <p><img src="https://i.stack.imgur.com/Bgpea.jpg" alt="Image with artifacts"></p>