What to do when a part of the background image becomes transparent when the transparent image is combined with Pillow
Preface
When I used Pillow to overlay PNG images of different sizes with ʻimg.paste`, the phenomenon that the transparency of the upper layer penetrated to the lower layer and the background was partially lost occurred, so a memo of how to deal with it.
environment
Python 3.8.2 Pillow 7.2 Ubuntu 20.04 on WSL2
Image you want to overlay with the background
Background (bg_cloudy.png)
Image you want to overlay (cloudy.png)
This has a problem in the background
However, if you try to overlap ʻimg with bg.paste`, it will expire.
from PIL import Image
bg = Image.open('bg_cloudy.png').convert('RGBA')
img = Image.open('cloudy.png').convert('RGBA')
bg.paste(img, (232, 412))
bg.save('a.png')
result
The background is also transparent in the transparent part of the cloud icon
approach
This can be avoided by using ʻImage.alpha_composite (bg, img)`. However, since the size of the image of the first argument and the image of the second argument must match, paste it at the specified position on the transparent image with nothing that has the same size as the background, and then overlay it. To do.
from PIL import Image
bg = Image.open('bg_cloudy.png').convert('RGBA')
img = Image.open('cloudy.png').convert('RGBA')
#Generate a transparent image the same size as the background
img_clear = Image.new("RGBA", bg.size, (255, 255, 255, 0))
#Paste on top of transparent image
img_clear.paste(img, (232, 412))
#Overlay
bg = Image.alpha_composite(bg, img_clear)
bg.save('a.png')
result
I was able to synthesize as intended without any problems in the transparent part.
reference
Image source
Image of clouds in the background https://www.priga.jp/ Icon cloud image https://github.com/twitter/twemoji
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