title: PNG with alpha-transparency to SVG with potrace
body: <p>I'm using <strong>potrace</strong> to convert a png file to svg. The png is black on transparent background with alpha-transparency levels. I would like to report them in the svg output. Is it possible ?
  Potrace skips the alpha-transparency and turns it to black.</p>
  
  <p>Here is my command:</p>
  
  <pre><code>convert -alpha Remove file.png pgm: | potrace --svg -o file.svg
  </code></pre>
  
  <p>PNG :
  <a href="http://i.imgur.com/d2ZYrf6.png" rel="nofollow">http://i.imgur.com/d2ZYrf6.png</a></p>
  
  <p>SVG output (.svg in reality but you can see directly the result in png) :
  <a href="http://i.imgur.com/n1NsNYQ.png" rel="nofollow">http://i.imgur.com/n1NsNYQ.png</a></p>
  
  <p>Thanks !</p>