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Re: [Opendivx] wavelets



Carlo, thanks for your enlightening post:
one thing... your percentages, when multiplied come to around 54% (I assume
you're meaning bitrates).  So, equivalent quality in half the size?  This
would incredible if we could do this :-)

John

----- Original Message -----
From: Carlo Daffara <[email protected]>
Cc: <[email protected]om>
Sent: Thursday, February 01, 2001 3:19 PM
Subject: Re: [Opendivx] wavelets


> Well, wavelets get much of their superiority from the fact that they tend
> not to show blocking effects (but they have a much worse ringing). If you
> use a good dct implementation (with adaptive quantization matrices) and a
> postprocessing filter you get exactly the same visual quality of wavelets
> on static images. When you use motion prediction methods (and
> differentials as a way to produce error images) wavelets no not have any
> advantage over dct for inter-frame coding. In fact, the use of wavelets
> is mainly for low bit rate coding, when compressing in the mid rate
> (400-900 kbit/s for 24/25 frames/sec, film like sources) the visual
> difference with dct is not perceptible.
> It is better to:
>
> - prefilter material to make the artifacts more acceptable, or to spread
> the error over different frames (warning- it seems that this is patented
> somehow) (approximate compression gain: 10%-15% depending on the material)
> - use a sophisticated motion matching algorithm; it is better *not* to use
> the block that minimize the RMS error, but to choose a block that does
> follow the optical flow of the moving sequence (there is a nice library
> from Intel that does it). Also, estimating the optical flow can be used
> for prefiltering (direction-oriented smoothing using constraint-based
> diffusion is used for this) (appr. gain: 15%)
> - use a postfilter to reduce the error created by the quantization step
> (there are several, good adaptive systems for that) (appr. gain: 20%)
> - if the material is to be seen from CDs or from broadband sources, you
> can allow a much larger VBR extension (appr. gain: 10%)
> DCT+Postfilter is roughly equivalent to DCT; there is an advantage thanks
> to hardware DCT implementation common in many graphic cards or thanks to
> the highly optimized libraries available for dct (there are none for
> wavelet).
> cheers
> Carlo Daffara
> Conecta Telematica
>
> On Thu, 1 Feb 2001, ridaas syncprodz.com wrote:
>
> > i have very few knowledge about video coding since my proper job is more
focused on transport-layer of mpeg standard (the so called mpeg2-TS).
> > i am not sure if mpeg4 standard talk or not about wavelets, maybe is
possible than more then one coding techinique is allowed.
> > what i know is this:
> >
> > -wavelet is based on subband coding, the wavelet transform scheme
combine transform coding with subband coding
> >
> > -wavelet is supposed to be very good for I-frame coding (same as jpeg
coding) and for low-bitrate videos (12-48kbps) the I-frame coding takes
about 40-70% of the bit used in the stream, this means that for very low
bitrate you save a lot respect typical dct.
> >
> > -wavelet is supposed to be more cpu intensive, i checked some article
and it seems the coder (on a dsp implementation) has 50% less framerate.
> >
> > -the problem with video and wavelet-based coding scheme is find a
mechanism to exploit the temporal redundancies and here i found 3 proposals:
> > 1) extensions of the 2-D wavelet-based scheme to 3-D subband coding (3-D
SBC)
> > 2) use of a multiresolutional motion compensation (MRMC) in the wavelet
domain
> > 3) so-called overlapped block motion compensation
> >
> > now don't ask me details cause i am not in this things at all :(
> >
> > good references can be found (where i found them, but there are lotsa of
article cited there) in this article:
> > "Very low bit-rate video coding using wavelet-based techniques" by
D.Marpe H.Cycon (IEEE Transactions on circuits and system for video
technology vol.9 feb 1999)
> >
> > i will check this wavelet things and mpeg4 and divx code (if i can
manage it) and will try to post my 2 cents when i will know more :)
> >
> > federico
> > ps: i thought divx was the microsoft hacked mpeg4 encoder btw..:)
>
>
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