knusperli

boundaries. The coefficients that Knusperli uses, would have rounded to the same values that are stored in the JPEG image.

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.