PIL: How to make area transparent in PNG?

Question

I've been using PIL to crop Images, now I also want to make certain rectangular areas transparent, say

from PIL import Image
im = Image.open("sample.png")
transparent_area = (50,80,100,200)
...

score 34 · Accepted Answer · edited Feb 29 '20 at 11:33

34

from PIL import Image
from PIL import ImageDraw
im = Image.open("image.png")
transparent_area = (50,80,100,200)

mask=Image.new('L', im.size, color=255)
draw=ImageDraw.Draw(mask) 
draw.rectangle(transparent_area, fill=0)
im.putalpha(mask)
im.save('/tmp/output.png')

I learned how to do this here.

edited Feb 29 '20 at 11:33

martineau

119,623
25
170
301

answered Dec 07 '10 at 19:08

unutbu

842,883
184
1,785
1,677

1

Upvoted you because the code follows pretty much exactly what I wrote. – kindall Dec 07 '10 at 20:13
Indeed, @kindall, our answers are pretty much identical! :) – unutbu Dec 07 '10 at 21:01

score 4 · Answer 2 · answered Dec 07 '10 at 18:47

No source code, but this is the general approach that should work: Create an alpha channel for the image in "L" (grayscale) mode as a separate image object. Fill the alpha channel with white (full opacity) and draw the rectangle on the alpha channel image in black (full transparency). Convert the image to which you want to apply the transparency to RGBA and use the image object putalpha() method to copy the alpha channel you created into the image's alpha channel. Save as PNG.

PIL: How to make area transparent in PNG?

2 Answers2

Linked