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Thread: Nonlinear transform coding?

  1. #1
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    Nonlinear transform coding?

    Just noticed looking interesting 8 author "Nonlinear Transform Coding" review paper from Google: https://arxiv.org/pdf/2007.03034.pdf
    Instead of linear transforms (left) like DCT, they want to use nonlinear (right) - e.g. from neural networks trained for rate-distortion optimization:




    Looks interesting, but I have doubts regarding practicality - beside much larger cost, it seems too complicated to exploit crucial context dependence - which rather (?) requires simpler models (e.g. ARMA-ARCH-like https://encode.su/threads/3452-Impro...CT-coeffcients ).

    Any thoughts? Can it be really practical?
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  2. #2
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    Quote Originally Posted by Jarek View Post
    Nonlinear Transform Coding
    https://arxiv.org/abs/2008.03936 could be another way to find similar non-linearities

    We tried three local non-linear transform approaches in JPEG XL development. Our conclusion was that it was difficult to get gains from them at the quality better than 8x the just-noticeable-difference. At 12-16x there was an improvement, but given our positioning of JPEG XL I did not want to add complexity that was only giving gains at very low qualities and being dead-weight at normal qualities.

    All of our efforts were simpler than the paper you show, i.e., piece-wise perspective transform on 64x64 blocks, rotated DCTs, directional regularization. Nothing worked well enough at high quality (in comparison to the additional format complexity and coding effort) to make it into the format.

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    Jarek (27th August 2020)

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