Making JPEG XS lossless

[Stefan Atev]

Hi, I just stumbled across this in my arxiv feed (https://arxiv.org/abs/2008.04558) and was wondering about the approach.

From what I understand, the idea is to use the visually lossless mode of JPEG XS to produce a base image, and then use another JPEG variant to encode the residual image (suitably rescaled).

My question: Does it make sense to use an algorithm designed for images on a residual image? It seems like the residual will not match the assumptions of most algorithms, indeed, it is almost uniquely designed not to match any assumptions about natural or computer-generated images. Am I missing something obvious?

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[MegaByte]

I'm not sure why they didn't test the JPEG XT Part 8 residual coder since that's what their design was based on (though I don't know if it would be appropriate for the residuals from JPEG XS).
The poor overall results might be mostly from the opposing design goal of JPEG XS (low latency, low complexity), but the less it was compressed by the JPEG XS layer, the more the other codecs were able to compress.