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> I can't tell if this applies to all or only converted ones JPEG-XL to JPEG is only lossless for JPEG-XL images which were upgraded from JPEG. Not all JPEG-X
by duskwuff 2y ago
> I can't tell if this applies to all or only converted ones
JPEG-XL to JPEG is only lossless for JPEG-XL images which were upgraded from JPEG.
Not all JPEG-XL images can even be represented as JPEG; in particular, images with more than three channels (like images with transparency, or images with CMYK color) or with multiple frames (like an animation) certainly can't.
- eviks 2y agoWhat about those that can be represented? Is it possible to convert lpsslessly by losing some compression efficiency or still only upgraded can be downgraded?
- pornel 2y agoJPEG XL has many compression modes inside, and the lossless JPEG roundtrip works only for one of them that was specifically designed to hold old JPEG's data. You can't take an arbitrary JXL file and turn it into a JPEG without lossy recompression. The old-JPEG-preserving compression mode also isn't the best that JXL can do. It's better than the old JPEG, but not as good as JXL using all the new bells and whistles.