P->RGBA->resize(LANCZOS)->P messes up transparency

What did you do?

Given original image
and following steps:

from PIL import Image
im = Image.open('test.png')
im.mode # 'P'
im = im.convert('RGBA')
im = im.resize((320,240), Image.LANCZOS)
im = im.convert('P')
im.save('broken.png')

What did you expect to happen?

What actually happened?

What versions of Pillow and Python are you using?

Python 2.7.13 / Pillow 4.2.1

However, if I slightly change the script and save RGBA image after convertion and resize to a file and then reopen that file, quantize it to palette, then it's all good:

from PIL import Image
im = Image.open('test.png')
im = im.convert('RGBA')
im = im.resize((320,240), Image.LANCZOS)
im.save('intermidiary.png')
intermidiary = Image.open('intermidiary.png')
intermidiary.mode # 'RGBA'
intermidiary = intermidiary.convert('P')
intermidiary.save('good.png')

Reproduced here. Bug is that the palette is still hanging around in the RGBA image:

(vpy27) erics@builder-16:~/test$ python -m pdb issue_2702.py
> /home/erics/test/issue_2702.py(1)<module>()
-> from PIL import Image
(Pdb) n
n
> /home/erics/test/issue_2702.py(2)<module>()
-> im = Image.open('issue_2702.png')
(Pdb) n
> /home/erics/test/issue_2702.py(3)<module>()
-> print im.mode # 'P'
(Pdb) n
P
> /home/erics/test/issue_2702.py(4)<module>()
-> im = im.convert('RGBA')
(Pdb) n
> /home/erics/test/issue_2702.py(5)<module>()
-> im = im.resize((320,240), Image.LANCZOS)
(Pdb) n
> /home/erics/test/issue_2702.py(6)<module>()
-> im.show()
[good image]
(Pdb) im
<PIL.Image.Image image mode=RGBA size=320x240 at 0x7F16BC7EAED0>
(Pdb) im.palette
<PIL.ImagePalette.ImagePalette object at 0x7f16bc7f7450>
(Pdb) im.palette = None
(Pdb) im.show()
[good image]

Workaround Code:

from PIL import Image
im = Image.open('issue_2702.png')
print im.mode # 'P'
im = im.convert('RGBA')
im.palette = None
im = im.resize((320,240), Image.LANCZOS)
im = im.convert('P')
im.save('issue_2702.out.png')

Remove palettes from non-palette modes in _new python-pillow#2702

Merge pull request #2704 from wiredfool/issue_2702

This fixes the issue for this image:

But the issue remains for this PNG:

Resizing results in something like this:

That's a different issue with another library.

@kkopachev

How do you mean @kkopachev?
I'm using Thumbor and this is happening. Does it not happen in PIL natively?

PIL is fine, it's issue in thumbor. I'll create PR there shortly.

Okay thanks. I'll work up a series of examples that are causing issues and post it there to ensure everything is captured.

@kkopachev

Hey @kkopachev, have you created a PR to fix this yet? I saw thumbor/thumbor#989, but this addresses something different.

@rogerchom

@rogerchom thumbor/thumbor#988

@kkopachev

@kkopachev Thanks!

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P->RGBA->resize(LANCZOS)->P messes up transparency #2702

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P->RGBA->resize(LANCZOS)->P messes up transparency #2702

Description

What did you do?

What did you expect to happen?

What actually happened?

What versions of Pillow and Python are you using?

Activity

wiredfool commented on Aug 31, 2017

onassar commented on Sep 23, 2017

kkopachev commented on Sep 25, 2017

onassar commented on Sep 25, 2017

kkopachev commented on Sep 25, 2017

onassar commented on Sep 25, 2017

rogerchom commented on Jan 22, 2018

kkopachev commented on Jan 22, 2018

rogerchom commented on Jan 23, 2018

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