Adding a transparent circle to an image on python with PIL

Question

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.

Here is what I do:

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Answer 1

Instead of a 3-tuple RGB value, (255, 128, 10), pass a 4-tuple RGBA value:

canvas.ellipse((p_x - 5, p_y - 5, p_x + 5, p_y + 5), 
               fill=(255, 128, 10, 50))

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For example,

import Image
import ImageDraw

img = Image.new('RGBA', size = (100, 100), color = (128, 128, 128, 255))
canvas = ImageDraw.Draw(img)

# Now I draw the circle:
p_x, p_y = 50, 50
canvas.ellipse((p_x - 5, p_y - 5, p_x + 5, p_y + 5), fill=(255, 128, 10, 50))

# now save and close
del canvas
img.save('/tmp/test.png', 'PNG')

Answer 2

I used Image.composite(background, foreground, mask) to mask a semi transparent circle on a foreground.

I followed the instructions from here: Merging background with transparent image in PIL

Thanks to @gareth-res