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by pornel
4566 days ago
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I'm trying to write a better JPEG compressor: https://github.com/pornel/jpeg-compressor IMHO JPEG algorithm isn't crude. IMHO it's actually quite brilliant—simple and very closely tied to human perception. The core concept of DCT quantization hasn't been beaten yet—even latest video codecs use it, just with tweaks on top like block prediction and better entropy coding. Wavelet compressors like JPEG 2000 beat JPEG only in lowest quality range where JPEG doesn't even try to compete. Wavelets seem great, because their blurring gives them high PSNR, but lack of texture and softened edges make them lose in human judgement. |
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The core trick isn't DCT per se, it is transform coding, Which both DCY and wavelets are, followed by (usually) quantization and then entropy coding.
Typical wavelets used are orthonormal transforms, no loss there. The "lack of texture and softened edges" are a choice of the model used, not a consequence of the transform. True also of DCT and blocking artifacts. This should be obvious since both approaches allow for lossless encoders.
Typically wavelets will beat or match JPEG in any situation both in terms of psnr and the like, and perceptually (though this latter is much more controversial and poorly defined -- and to be fair I am not up to date on the literature here but I would be surprised of that has changed in the last decade).
The real reason for the huge popularity of DCT in still compression at first and video codecs later is that it is cheap to implement in hardware. And once there becomes very cheap to use.
JPEG 2000 is needlessly complex, at its core a wavelet codec is also very simple and elegant.