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Prevent masking of Image reduce method in Jpeg2KImagePlugin #4474

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merged 4 commits into from Mar 29, 2020

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@radarhere radarhere commented Mar 14, 2020

Resolves #4343. Alternative to #4344

The new Image reduce method does not work for Jpeg2K images, as Jpeg2KImagePlugin has a reduce variable that masks it. The variable is not purely internal, but is actually tested behaviour -

def test_reduce(self):
with Image.open("Tests/images/test-card-lossless.jp2") as im:
im.reduce = 2
im.load()
self.assertEqual(im.size, (160, 120))

PR #4344 tried to address this by treating the setting of reduce as an integer, and the use of reduce as a method, as two different scenarios that were not to interact.

So instead, this PR changes Pillow so that if you set reduce as an integer, the user will then see reduce as an integer.

with Image.open("Tests/images/test-card-lossless.jp2") as im:
        assert callable(im.reduce)

        im.reduce = 2
        assert im.reduce == 2

At that point, you can't call the reduce method externally. If Pillow tries to call the reduce method internally though, it will ignore this new use of reduce, and still call the Pillow method.

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Like this

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@python-pillow python-pillow deleted a comment from codecov bot Mar 20, 2020
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@radarhere
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@homm so you approve of this PR then?

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homm commented Mar 20, 2020

What about deprecation warnings?

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homm commented Mar 24, 2020

What about deprecation warnings?

Otherwise is ok.

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Ok, I've added a deprecation warning pointing users to use load_reduce instead.

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homm commented Mar 24, 2020

I believe, load_reduce is not the way how it should work. There is already .draft() method exactly for this functionality, which should be used.

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Correct me if I'm wrong - there isn't a draft method for Jpeg2kImagePlugin. It only exists for JpegImagePlugin.

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homm commented Mar 25, 2020

Draft method exists for PIL.Image.Image. It "configures the image file loader so it returns a version of the image that as closely as possible matches the given mode and size". This is exactly what Jpeg2KImageFile.reduce was erroneously used for.

To be clear: I don't mean you have to implement Jpeg2KImageFile.draft() method to fix this bug, I just strongly against adding extra API for things that already exist.

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Sure, sure. I'm just confused about the idea of adding a deprecation warning without being able to tell them what they should be doing instead.

I've removed load_reduce and the deprecation warning. How do you feel about merging this in for 7.1.0, to resolve #4343 and then maybe we introduce a deprecation warning and a Jpeg2K method at a later date?

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This was referenced Mar 17, 2021
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JPEG 2000 file cannot be Image.reduce() 'd
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