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JPEG XL supports lossless JPEG transcode, so it has to offer a superset of the features in JPEG.
by edflsafoiewq 2y ago
JPEG XL supports lossless JPEG transcode, so it has to offer a superset of the features in JPEG.
- aidenn0 2y agoYes, but variable-blocksize DCT is definitely used in the lossy modes (not sure about lossless).
- edflsafoiewq 2y agoYeah, JPEG uses the DCT, so JPEG XL needs it too to be a superset.
- aidenn0 2y agoYes, but if the DCT were purely vestigial, then: 1. It wouldn't have support for DCTs not in JPEG. 2. It wouldn't use the DCT in its lossy-compression of photographic content if another transform was considered significantly better. Perhaps one could argue that they didn't want to add extra transforms, but they do use a modified Haar transform for e.g. synthetic content and alpha channels.
- lifthrasiir 2y agoThe squeeze transform used for extra progressive decoding is effectively a modified Haar transform.