title: Converting PNG32 to PNG8 with PIL while preserving transparency
body: <p>I would like to convert a PNG32 image (with transparency) to PNG8 with Python Image Library.
  So far I have succeeded converting to PNG8 with a solid background.</p>
  
  <p>Below is what I am doing:</p>
  
  <pre><code>from PIL import Image
  im = Image.open("logo_256.png")
  im = im.convert('RGB').convert('P', palette=Image.ADAPTIVE, colors=255)
  im.save("logo_py.png", colors=255)
  </code></pre>