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Use disposal settings from previous frame in APNG#5126

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hugovk merged 1 commit intopython-pillow:masterfrom
radarhere:apng_disposal
Dec 31, 2020
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Use disposal settings from previous frame in APNG#5126
hugovk merged 1 commit intopython-pillow:masterfrom
radarhere:apng_disposal

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@radarhere radarhere commented Dec 23, 2020 •
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Helps the APNG part of #5032. Alternative to #5071

Resolves #4657

At the moment, self.dispose_op and self.dispose_extent are set in _seek,

Pillow/src/PIL/PngImagePlugin.py

Lines 854 to 856 in ce3d80e

self.dispose_op = self.info.get("disposal")
self.blend_op = self.info.get("blend")
self.dispose_extent = self.info.get("bbox")

and then used in _load_end

Pillow/src/PIL/PngImagePlugin.py

Lines 946 to 953 in ce3d80e

if self.dispose_op == APNG_DISPOSE_OP_PREVIOUS:
dispose = self._prev_im.copy()
dispose = self._crop(dispose, self.dispose_extent)
elif self.dispose_op == APNG_DISPOSE_OP_BACKGROUND:
dispose = Image.core.fill(self.im.mode, self.size)
dispose = self._crop(dispose, self.dispose_extent)
else:
dispose = None

This should not be the case, as the specification states that

dispose_op specifies how the output buffer should be changed at the end of the delay (before rendering the next frame).

It controls how the contents of the current frame should be disposed when moving on to the next frame. It is not something to be immediately applied.

This PR corrects that.

This was referenced Dec 23, 2020
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@hugovk hugovk merged commit 4093897 into python-pillow:master Dec 31, 2020
@radarhere radarhere deleted the apng_disposal branch January 2, 2021 01:09
This was referenced Mar 8, 2021
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@dependabot dependabot bot mentioned this pull request Mar 17, 2021
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APNG conversion issue

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@radarhere @hugovk