Deprecate saving I mode images as PNG - #9023
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hugovk merged 2 commits intoJun 21, 2025
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hugovk
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Jun 17, 2025
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docs/deprecations.rst
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| In order to fit the 32 bits of I mode images into PNG, when PNG images can only contain | ||
| at most 16 bits for a channel, Pillow has been clipping the values. Rather than quietly | ||
| changing the data, this is now deprecated. |
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Can we give advice on what people should do instead?
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I've updated the commit to append
Instead, the image can be converted to another mode before saving::
from PIL import Image
im = Image.new("I", (1, 1))
im.convert("I;16").save("out.png")
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I noticed that the deprecation warning wasn't being emitted for from PIL import Image
im = Image.new("I", (1, 1))
im.save("out.png")This is because the call to deprecate() isn't in the function that the user calls (im.save()), it's one level deeper than that (PngImagePlugin._save). I've added a commit to pass a custom stacklevel to deprecate(). |
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Resolves #9022
PNG images can only have a maximum of 16 bits per channel - https://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html
However, Pillow still allows saving PNG images as I mode, by clipping the data.
The issue has requested that we prevent this automatic transformation, so this PR deprecates it.