title: Python PIL - All areas of PNG with opacity > 0 have their opacity set to 1
body: <p>Imagine a red circle with a black dropshadow that fades away on top of a fully transparent background. When I open and resave the image with PIL the background remains fully transparent but the dropshadow becomes full black.</p>
  
  <p>The problem appears without even altering the image:</p>
  
  <pre><code>image = Image.open('input.png')
  image = image.convert('RGBA')
  image.save('output.png')
  </code></pre>
  
  <p>I want to keep the image looking exactly as the original so that I can crop or resize it.</p>
  
  <p>EDIT: Here's a PNG that demonstrates the effect. It was converted to 8bit by using PNGNQ.</p>
  
  <p><img src="https://i.stack.imgur.com/kHrY6.png" alt="alt text"></p>
  
  <p>When using the above Python code it comes out as the following:</p>
  
  <p><img src="https://i.stack.imgur.com/IfRAx.png" alt="alt text"></p>