That's just by changing the entropy coder and retaining the DCT coefficients. The idea is similar to Dropbox's Lepton. https://dropbox.tech/infrastructure/lepton-image-compression...
replyThe main difference being that Lepton is worse and 100x slower.
replyLepton guarantees that JPEG->Lepton->JPEG produces an identical file, not just identical pixels. Does JPEG XL achieve the same thing?
replyYes
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