[theora] NHW Codec - aliasing

Raphael Canut nhwcodec at gmail.com
Sat May 27 14:30:38 UTC 2017


I have just tested new next lower quality settings (-l3 and -l4), I can
diminish residual coding but if I increase wavelet coeffs threshold there
is more aliasing.And even in the current mid quality settings there is some
aliasing, this is the big drawback of the NHW codec.

SPIHT algorithm is good for that as for example Rududu codec doesn't have
aliasing at all at mid compression and then it appears slightly at high
compression.So I will have to study it in details.

The main advantage of the NHW codec is that it is very fast, but there is
some aliasing, artifacts.The NHW Project after more than 7 years of
existence can be considered as dead now but it wouldn't have been pointless
because it introduced somme innovations, like a new fast wavelet transform
(the fastest DWT implementation I have seen), a new multistage residual
coding, and 3 new entropy coding schemes.There were also other very good
codecs that didn't lead to commercial products and that disappeared now, to
name a few there are the very good: Rududu Image Compression (2008), UCI
(x264 intra, 2008) and DLI compression (2009).Their authors seem to have
abandonned, stopped promoting their codec since 2012.

Now it is the turn to the NHW Project I think, I will try to improve it,
notably try to correct the aliasing and artifacts when I have time, it will
be a good hobby.Because of the current aliasing it is not suited for
photography.It could have been a good video codec for mobile devices as it
is very fast, but if mobile devices don't adopt AOM AV1 or HEVC, they will
simply stick with H.264 that is very good.So I don't see a commercial use
for the NHW codec, there is also no community around the codec, so I think
it will disappear now and it won't be the first.

I will try sometimes to post some updates but it will be quite difficult as
I hardly have the time.

Many thanks to the Xiph Theora channel!
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