Image pasted with PIL produces artifacts

Question

I have a bunch of images I need to put a text-overlay on top of. I created the overlay with GIMP (PNG with transparency) and tried pasting it on top of the other image:

from PIL import Image

background = Image.open("hahn_echo_1.png")
foreground = Image.open("overlay_step_3.png")

background.paste(foreground, (0, 0), foreground)
background.save("abc.png")

However, instead of displaying a nice black text on top, I get this:

overlay.png looks like this in Gimp:

So I would expect some nice and black text instead of this colorful mess.

Any ideas? Some PIL option I am missing?

Have you tried `alpha_composite`? See [this answer](http://stackoverflow.com/a/15919897/4241180) — vrs, Jan 03 '16 at 14:55
Damn, thanks. I came from this answer but didn't scroll any further... — user3696412, Jan 03 '16 at 15:00

score 5 · Accepted Answer · edited May 23 '17 at 12:25

5

As vrs pointed out above, using alpha_composite like this answer: How to merge a transparent png image with another image using PIL

does the trick. Make sure to have the images in the correct mode (RGBA).

Complete solution:

from PIL import Image

background = Image.open("hahn_echo_1.png").convert("RGBA")
foreground = Image.open("overlay_step_3.png").convert("RGBA")
print(background.mode)
print(foreground.mode)

Image.alpha_composite(background, foreground).save("abc.png")

Result:

edited May 23 '17 at 12:25

Community

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answered Jan 03 '16 at 15:03

user3696412

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It sure looks like a palette problem - GIMP can't handle indexed PNG images with partial transparence - so, I'd say OP's background image is an indexed.png and PIL is forcing the overlay to indexed in a wrong way when pasting with `.paste`. I'd say that simply applying the `.convert` step on teh background would work for the OP. – jsbueno Jan 04 '16 at 13:18

Image pasted with PIL produces artifacts

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