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I did some (unpublished) experiments a few years ago comparing J2K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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