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The separate lossless codec and FUIF and some additional ideas have been integrated into the modular mode. The modular mode and VarDCT can be mixed in the same

The separate lossless codec and FUIF and some additional ideas have been integrated into the modular mode. The modular mode and VarDCT can be mixed in the same image. JPEG XL decoder no longer performs 'quantization constraint', it is a classic loop filter, just with heuristics and control fields to maintain detail much better than loop filters in video codecs. If you start with sharp high quality originals that don't have yuv420 in them, you usually will see 65 % savings with JPEG XL, i.e. more than 30 % on top of brunsli. You can think of VarDCT-mode as guetzli(-35 %) + brunsli(-22 %) + format specific changes(-30 %) like variable sized dcts, better colorspace, adaptive quantization and loop filtering.

twotwotwo 7y ago
Thanks, I appreciate the corrections and detail. I was mostly going by the committee draft on the arXiv (https://arxiv.org/abs/1908.03565 https://arxiv.org/abs/1908.03565 ), which still mentioned the quantization constraint (J.3) and a "mathematically lossless" mode (annex O) distinct from modular. "Four formats" was just imprecise wording on my part. The material already public about JPEG XL's design rationale, testing, and so on has been really fun to follow as an outsider. I selfishly hope there's more of it as the work on it and rollout continue. Even with the standard itself public, a lot can be mysterious to those not immersed in this stuff.
- janwas 7y ago
  Yes, quantization constraint was removed post-CD and Annex O was recently merged into the modular mode to simplify the standard. JXL's page count is 1/2 to 1/3 of contemporary video codecs.
  - twotwotwo 7y ago
    Thanks. If there are places the public can follow progress post-CD, I'm curious. (I see https://gitlab.com/wg1/jpeg-xl/ https://gitlab.com/wg1/jpeg-xl/ was updated late Feb, yay.)
    - janwas 7y ago
      :) There are updates every ~3 months at https://jpeg.org/news.html https://jpeg.org/news.html.

twotwotwo 7y ago

Thanks, I appreciate the corrections and detail. I was mostly going by the committee draft on the arXiv (https://arxiv.org/abs/1908.03565 https://arxiv.org/abs/1908.03565 ), which still mentioned the quantization constraint (J.3) and a "mathematically lossless" mode (annex O) distinct from modular. "Four formats" was just imprecise wording on my part. The material already public about JPEG XL's design rationale, testing, and so on has been really fun to follow as an outsider. I selfishly hope there's more of it as the work on it and rollout continue. Even with the standard itself public, a lot can be mysterious to those not immersed in this stuff.

janwas 7y ago
Yes, quantization constraint was removed post-CD and Annex O was recently merged into the modular mode to simplify the standard. JXL's page count is 1/2 to 1/3 of contemporary video codecs.
- twotwotwo 7y ago
  Thanks. If there are places the public can follow progress post-CD, I'm curious. (I see https://gitlab.com/wg1/jpeg-xl/ https://gitlab.com/wg1/jpeg-xl/ was updated late Feb, yay.)
  - janwas 7y ago
    :) There are updates every ~3 months at https://jpeg.org/news.html https://jpeg.org/news.html.