PIL - Image Paste On Another Image With Alpha

Question

I'm struggling a touch with pasting one image with a transparent background on another, also with a transparent background, with the right alpha/colour blending.

Here are some example images, red.png and blue.png:

I want to paste blue.png on top of red.png, and achieve this effect:

That image was made by combining the two images in Photoshop, simply as two layers.

The closest I can get using the Python Imaging Library is:

with this code:

from PIL import Image

blue = Image.open("blue.png")
red = Image.open("red.png")
red.paste(blue, (0,0), blue)
red.save("result.png")

Do you see how the alpha and the colour is off where the two circles overlap? In the expected result image, the red and blue blends together in a purplish way, but there's an unwanted alpha halo in the actual result image.

How can I achieve my ideal result in PIL?

Answer 1

The closest I got was to use the alpha_composite function found here. Works really rather well!