title: Adding a transparent circle to an image on python with PIL
body: <p>I have a python program that craetes a png file with a circle on it. Now I want this circle to be semi transparent, given an alpha value. </p>
  
  <p>Here is what I do:</p>
  
  <pre><code>img_map = Image.new(some arguments here)
  tile = Image.open('tile.png')
  img_map.paste(tile, (x,y))
  canvas = ImageDraw.Draw(img_map)
  
  # Now I draw the circle:
  canvas.ellipse((p_x - 5, p_y - 5, p_x + 5, p_y + 5), fill=(255, 128, 10))
  
  # now save and close
  del canvas
  img_map.save(path_out + file_name, 'PNG')
  </code></pre>
  
  <p>how can I make the ellipse semi transparent? </p>
  
  <p>Thanks</p>