macOS: Lossless PNG encoding randomly producing extreme small files about jxl-coder-swift HOT 10 CLOSED

I've tried your demo but I still getting a constant result.
May I have some sample image? Do you use x86 Intel mac or M* Apple Silicon?

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Try 1.3.2 version. I think it may solve the issue

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Still repros on 1.3.2. I tried multiple files, some never hit this. One particular file seems to have a much higher chance.

I'm on M2 Pro, macOS 13.5.1 (22G90)

Attached the zip of that file:

1.zip

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Try out 1.3.3 version. It should works correctly

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Upgraded to 1.3.3, now it's 100% 33KB instead of 166KB:

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Yes, it is expected. Bug was producing invalid background colors that was increasing a file size

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Both cjxl -q 100 and squoosh.app (lossless) produce a 177KB jxl

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Yes, because it may detect that original file uses RGBA ( 4 channel with alpha ) and compress it in RGBA. If you'll set colorSpace: .rgba in encoder parameters you will get close result to it. Default value is rgb that replaces alpha channel to black that you may have already noticed in result files. I add that implicit option to choose compressing in RGB or RGBA since in Apple platform almost no clear ways to understand original pixel format because it must be always be redrawn in premultiplied RGBA pixel format. And RGB was chosen as default because primary target of JPEG XL is photos that do not contains alpha channel.

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So the main responsibility to choose between RGB or RGBA pixel format is delegated to the caller

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I see. Thanks for the explanation. Can confirm it's working after switching to .rgba.

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