[theora] NHW codec - progress 2

Raphael Canut nhwcodec at gmail.com
Mon May 16 14:38:54 UTC 2016


Sorry for the late answer.I don't have advanced with low contrast
information coding in the NHW codec, primarily because I can not target
specifically these areas... But I think it's a choice, between neatness and
precision, and it's not the same algorithms for each.I have chosen a new
approach: neatness, to (try to) bring a new point of view for image
compression, and it can be half-successful actually, because at -h2 setting
for the nhw codec where there is full-neatness, results are visually better
for me than BPG (HEVC intra), WebP, and other codecs...

But the NHW codec doesn't scale very well to high compression.In this
domain, AOM AV1, HEVC and VP10 are monsters of compression, while still
keeping the CABAC entropy coding to ensure a "fast", reasonnable
decoding.Very quickly, is that true? I have read on another forum that
Google VP9/10 and then AOM AV1 use the CABAC entropy coding scheme as in
HEVC.I have checked the code rapidly, and I can see the subexp (exp-golomb)
binarization, the lookup-table-based arithmetic coding,... But this must be
untrue because AOMedia and Google claim their works are royalty-free (while
the CABAC scheme is heavily patented)... Any clarification would be welcome.

To quickly finish, the other great advantage of the NHW codec is that it is
fast, a lot faster than these codecs above... But can not compete with them
for high compression...


2016-03-24 17:15 GMT+01:00 Raphael Canut <nhwcodec at gmail.com>:

> Hello,
> Just a quick message to correct what I have said in my previous post.It
> finally seems not that easy to code small wavelet coefficients to have a
> good precision, and SPIHT is certainly a very good algorithm for that, -and
> I know there are SPIHT experts that can make very good SPIHT-based
> codecs-.I have chosen a new and different approach, the multistage residual
> coding, so I will try to keep it and get the best of it.
> I estimate that I need an additional 10Ko in average to code low contrast
> information (and avoid artifacts).So I will need to remove 10Ko of
> information in high contrast and give it to low contrast.I think in a first
> time, I will only use residual coding for the low contrast area errors.I
> will try to do this next month if I can find time, and will let you know
> what it gives.
> I am also aware that with all this, it will be very very difficult to beat
> HEVC, VP9/10, Daala.The entropy coding is certainly the most interesting
> part of my codec.
> Cheers,
> Raphael
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