Hi Vladimir,
Thanks for the update. It is useful to know that
your initial results are in line with my previous
experiments (after allowing for your improvements
to arithmetic coding). Of course the processing
times are not representative of practical use
since DiracEncoder and, I presume, your software
were designed for algorithm testing not
efficiency. Nevertheless the 40% requirement for
the arithmetic coding does not seem out of line.
For more detailed information about a practical
implementation you'll need to talk to David Schleef.
Please do keep in touch.
BR
Tim
At 23:18 28/11/2010, javasharp...@ukr.net wrote:
Hi Tim, All
so I'm back with an update.
First of all my comparison was not pure j2k vs
dirac. Instead I took j2k spec as base (but I
didnt reuse their codebase), replaced the qcoder
with real arithmetic and added some lightweight
compression optimizations. The testing was made
so far on a single file CITY
(http://media.xiph.org/video/derf/) which was
converted from 4CIF to 512x512 (limitation of my
implementation so far) in intra-only mode. The
result is: my codec compresses about 2,5%
better. My calculations show that this is the
job of my optimizations, so I think it would be
quite realistic to say that j2k + arith does same as dirac.
Timing: on my dell studio 1749 my codec spent
1.97701 sec/frame in average while native dirac
spent 1.7084 sec/frame as reported by EncodeDirac.exe.
It would be interesting to know how much
Schrodinger is faster (probably I will try it if
it compiles on Windows) because while my current
implementation is just horrible I noticed that
about 40% of time is consumed by arithmetic
coder code which is more or less optimal...
BR,
Vladimir
--- Èñõîäíîå ñîîáùåíèå ---
Îò êîãî: "Tim Borer" <tim.bo...@bbc.co.uk>
Êîìó: javasharp...@ukr.net, schrodinger-devel@lists.sourceforge.net
Äàòà: 1 íîÿáðÿ 2010, 12:30:40
Òåìà: Re: [Schrodinger-devel] dirac vs jpeg2k entropy modelling
Hi,
I would be interested to hear the results of
experiments comparing Dirac Pro and J2K. I
assume you will be comparing Intra Dirac, i.e. Dirac Pro/SMPTE VC-2, with J2K?
As you say Dirac Pro's entropy modelling is
quite different to J2K. I doubt it yields a
higher compression ratio - the objective with
Dirac Pro was to produce a simpler, less complex
solution rather than a higher compression ratio.
However I would add that, because Dirac Pro
takes care to preserve the DC precision it can
have fewer visual artefacts than J2k (even if
PSNR figures don't show this). I say this
because we have noticed that J2K, used for
video, can produce an annoying DC flicker even at quite low compression ratios.
I did some (unpublished) experiments a few years
ago comparing J2K and Dirac Pro. With arithmetic
coding enabled the compression efficiency (for
lossless coding) was almost identical for the
two codecs (some images were 1 or 2% better with
one codec and the other way round for other
images). Interestingly when arithmetic coding
was disabled, so that entropy coding was only
the fixed variable length coding (interleaved
exp-Golomb), the compression efficiency of Dirac
Pro only dropped by 20%. That is for lossless
coding arithmetic coding only appeared to give a
compression gain of 1.25. Given that arithmetic
coding adds significantly to the complexity of
the codec some applications may prefer the
option of not using arithmetic coding in Dirac
Pro for lower complexity at the expense of slightly reduced compression.
At the moment there are low delay profile
hardware implementations of Dirac Pro/SMPTE VC-2
available from Numedia Technology and from
Westwood Rock. Software implementations are
available in the Open Source Schroedinger software and from Entropy Wave.
Regards
Tim
Dr Tim Borer
Lead Engineer
BBC Research & Development
BBC Centre House
56 Wood Lane
London W12 7SB
At 20:46 30/10/2010, javasharp...@ukr.net wrote:
Hi,
I want to do some experiments with dirac and
j2k and I have a question. As I see dirac's
entropy modelling is totally different from
that of j2k. It would be interesting to know
the rationale behind it. In particular if the
j2k's entropy modelling (together with the
dirac's arithmetic encoder which as I
understans is more effective than j2k's
quasi-arithmetic encoder) what size decrease can be expected?
Thanks in advance,
Vladimir
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