APNG conversion issue

[karolyi]

Hey,

I tried to convert an APNG with Pillow and got a bad looking output. It seems that WEBP saving works a bit better but there are also problems. This issue is about converting an APNG into an APNG while having the same watermarking/thumbnailing as in #4644. I've attached a self-contained test code apng-test.zip to reproduce the problem.

The used APNG is downloaded from https://en.wikipedia.org/wiki/APNG, the wikipedia article about APNG formats.

Hope to get this fixed soon, because I have to convert all APNG-s into WEBPs to be able to look half decent.

[radarhere]

While I recognise the output is still not good, on a practical level, I found that if you remove disposals from your save arguments, the disappearing effect is fixed.

[karolyi]

Interesting. Can you post the adjusted code please? I thought the disposal argument in the save_kwargs is that one.

[karolyi]

Oh, I misread, my bad. It's actually removing that argument that helps? Odd, one would think you'd have to add that back to the save parameters.

[karolyi]

Even if you remove the watermarking, you'll get a bad looking result after conversion:

[radarhere]

I find that if you remove disposals from the save arguments, and run your code with #5126, the result looks correct.

[radarhere]

I think the reason that you don't need disposals when saving is that Pillow isn't giving you each frame as it was originally encoded, as a series of cropped regions to be combined later - it's applying disposals and blends to give you the combined result that a user would see.

So by the same logic you shouldn't need blend when saving either.

[radarhere]

This should now be fixed in Pillow 8.1.0, due to be released in the next day or so.

[karolyi]

Hey,

it's a bit belated but can confirm it works with Pillow 10.x :)