[theora] NHW Project - lower quality settings - high compression

Raphael Canut nhwcodec at gmail.com
Mon Dec 11 15:34:03 UTC 2017


I was testing quickly some other lower quality settings -l3, -l4 because
high compression is what really lacks to the NHW codec.

In fact I can remove -5Ko of residual coding on Y,U,V comps for -l3 and I
can remove -10Ko always of residual coding for -l4, and -l3, -l4 settings
will be really better than the current ones implemented.

I can also increase the wavelet coefficients threshold (of the dead zone),
currently it is 8, can increase to 9,10,11,12,... according to the
compression wanted.The problem with this operation is that I will increase
aliasing and it will become no more acceptable... I have coded a
post-processing function in the NHW decoder that is supposed to remove
aliasing but it doesn't work at all (and I still haven't removed
it...).Would you know an efficient processing, algorithm that removes
aliaising? It would help me a lot!!!

Because the next quality settings could be here: -l3,-l4,-l5,-l6 with
-5Ko,-10Ko,-15Ko,-20Ko corresponding roughly to 1.5bpp->1bpp (for image not
video) with the processings explained above.

Then for the next settings, I could start to increase quantization of the
DC parts, and have a better analysis of wavelet coefficients, this is the
most difficult part.

So again, I think it will finally not be so difficult to go down to 1bpp
but it implies to have a post-processing that removes aliasing? What do you
think of this approach?

Any help is very welcome!

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