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Interestingly enough, JPEG XR used a form of the Hadamard Transformation, but JPEG XL (which is newer) uses DCT and Haar transforms. [edit] Combined with the
by aidenn0 2y ago
Interestingly enough, JPEG XR used a form of the Hadamard Transformation, but JPEG XL (which is newer) uses DCT and Haar transforms.
[edit]
Combined with the information from sibling comments, it seems that the Hadamard transform was something used in standards developed in the '00s but not since.
- adgjlsfhk1 2y agoprobably because multiplication got really fast
- edflsafoiewq 2y agoJPEG 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.
- lifthrasiir 2y agoWHT is essentially a cheap implementation of multi-dimensional DCT, so it approximates but doesn't actually replace DCT in all scenarios. It seems that DCT is a better fit for photographic contents than WHT but was more expensive until FP multiplication became much cheaper so WHT was briefly considered as an alternative.