XnView Software

XnView: MP 1.6.2 - 64 bit
OS: Windows

The recent update to the development version of the JPEG-XL decoder is not backward compatible - to be specifiic, the older decoder has a bug that didn't matter up until now. Alas, all images encoded with 0.10 are not readable anyore, so the lib for XnViewMP needs an update. The respecive fix is 1.5 years old: https://github.com/libjxl/libjxl/issues/1478

Here's the respective libjxl bug ticket, the dev descibes the issue: https://github.com/libjxl/libjxl/issues/2995

Effect: Images encoded with the latest JPEG-XL encoder aren't readable in XnView-MP (or any other app apparantly that uses an older decoder lib).

To reproduce:
1. Encode image with JPEG-XL 0.10
2. Try to read encoded image with XnView containing decoder lib

Actual behaviour (bug): Image is not readable

Expected behaviour: Image is readable

currently 0.8.2 is used

I do not know how many photos you have in Jpeg XL format.
I encoded some jpeg pictures with an early version of jpeg xl 0.30.
To get the best compatibility to newer releases of jpeg xl library,
I decoded my very old jpeg xl files to jpeg format again (without recompression) and transcoded them with the latest jpeg xl encoder (without quality loss) again.

I think you will get somewhere your old jxl 0.10 decoder/encoder to convert your files to jpeg again.