TWtwotwotwo·Oct 7, 2019
A potential future option I only just learned about is JPEG XL (not XR!) which is proposed as a royalty-free successor to the JPEG we know. The draft is at https://arxiv.org/abs/1908.03565 and a little bit about what it has and why is at https://www.spiedigitallibrary.org/conference-proceedings-of... (but I haven't found nearly as much public detail on tools, reasoning behind choices, etc. as there is for e.g. AV1).
The most interesting bit of it is that it contains a JPEG1 recompressor that saves about 20% space but allows exact reconstruction of the original file. It uses more modern entropy coding and goes to more effort to predict coefficients than JPEG1. It has almost exactly the same gains as, and sounds a lot like, Dropbox's Lepton, described here: https://blogs.dropbox.com/tech/2016/07/lepton-image-compress... .
Seems like a big d
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eal to plug seamlessly into all the JPEG-producing stuff that exists, without either doing a second lossy step (ick) or forking into two versions when you first compress the high-quality original. 20% off JPEG sizes is also a bigger deal than it may sound like; totally new codecs with slower encodes and a bucket of new tools only hit like ~50% of JPEG sizes. As Daala researcher Tim Terriberry once said, "JPEG is alien technology from the future." :)
For JPEG XL's native lossy compression, it has some tools reminiscent of AV1 and other recent codecs, e.g. variable-sized DCTs, an identity transform for fundamentally DCT-unfriendly content, a somewhat mysterious 4x4 "AFV" transform that's supposed to help encode diagonal lines (huh!), a post-filter to reduce ringing (that cleverly uses the quantization ranges as a constraint, like the Knusperli deblocker: https://github.com/google/knusperli ).
Interestingly it does not use spatial prediction in the style of the video codecs. A developer in a conference presentation mentioned that it's targeting relatively high qualities equivalent to ~2bpp JPEGs -- maybe spatial prediction just doesn't help as much at that level?
Don't know if AV1-based compression or JPEG XL will get wide adoption first, but either way we should actually have some substantial wins coming.