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Re: [Opendivx] wavelets
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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http://www.syncprodz.com
------(mp3 since 1997)-------
-----Original Message-----
From: John Funnell [email protected]
Sent: Thu, 1 Feb 2001 09:46:45 -0000
To: [email protected], [email protected], [email protected]
CC: [email protected]
Subject: Re: [Opendivx] wavelets
Federico,
Do you know if there were studies done to prove that wavelets would not be
better than dct? And has the situation changed now - are there new wavelet
(or perhaps matching pursuits) schemes that could outperform dct?
In fact, it could be said that the dct scheme we have is wavelet based! The
definition of a wavelet actually encompasses dct basis functions.
So, DivX uses wavelet compression ;-)
Tell me if you agree/disagree!
John
----- Original Message -----
From: ridaas syncprodz.com <[email protected]>
To: <[email protected]>; <[email protected]>
Cc: <[email protected]>
Sent: Thursday, February 01, 2001 9:10 AM
Subject: Re: [Opendivx] Reusability
wavelet is very good for still images, it will be the major point of the
coming jpeg2000 standard.
for mpeg4 they (mpeg group) talked about putting wavelet but they saw the
added complexity will not increse the performance since with video wavelet
and dct works quite the same.
federico
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