title: Overlay two same sized images in Python
body: <p>I've got two images that are exactly the same dimensions, all I'm trying to do is take one, make it 50% transparent and place it directly on top of the other, like so:</p>
  
  <pre><code>import Image
  
  background = Image.open("bg.png")
  overlay = Image.open("over.png")
  
  background = background.convert("RGBA")
  overlay = overlay.convert("RGBA")
  
  background_pixels = background.load()
  overlay_pixels = overlay.load()
  
  for y in xrange(overlay.size[1]):
      for x in xrange(overlay.size[0]):
           background_pixels[x,y] = (background_pixels[x,y][0], background_pixels[x,y][1], background_pixels[x,y][2], 255)
  
  for y in xrange(overlay.size[1]):
      for x in xrange(overlay.size[0]):
           overlay_pixels[x,y] = (overlay_pixels[x,y][0], overlay_pixels[x,y][1], overlay_pixels[x,y][2], 128)
  
  background.paste(overlay)
  background.save("new.png","PNG")
  </code></pre>
  
  <p>But all I get is the 50% transparent overlay (so half way there!).</p>