[Mp4-tech] RE: Why spatial prediction in AVC performed in pixel domain?

[Shevach Riabtsev]

Thanks Gary
Actually you answered my query. Indeed if one block is in Inter MB and
other block belongs to Intra MB, then no correlation in frequency domain
between the blocks expected. 
I missed this point. 
Regards,  Shevach
Broadcom
________________________________
From: Gary Sullivan [mailto:garysull windows.microsoft.com] 
Sent: Wednesday, August 29, 2023 4:21 PM
To: Shevach Riabtsev
Cc: mp4-tech lists.mpegif.org
Subject: RE: Why spatial prediction in AVC performed in pixel domain?
Shevach et al,
The Q15 documents should be found at
http://ftp3.itu.int/av-arch/video-site.  Look in the folders for 1998.
The measurement you did sounds excessively simplistic.  You did not
demonstrate an actual compression system with real syntax design and
actual selection of which prediction mode will be used and test the
compression performance in the rate-distortion sense.  Just measuring
correlation is not enough.
I am pretty confident that we would not be using the spatial prediction
scheme if the old frequency-domain prediction scheme like what is found
in H.263 Annex I and MPEG-4 part 2 would have worked better.
Note also that the frequency-domain prediction scheme has a problem if
the neighbor is not intra coded.
Best Regards,
Gary Sullivan
________________________________
	From: Shevach Riabtsev [mailto:sriabtsev broadcom.com] 
	Sent: Wednesday, August 29, 2023 4:52 AM
	To: Gary Sullivan
	Cc: mp4-tech lists.mpegif.org
	Subject: RE: Why spatial prediction in AVC performed in pixel
domain?
	Gary
	I compared correlation coefficients among neighboring 4x4 blocks
in both sample domain and frequency one (i.e. quantized coefficients).
It appears that the correlation in frequency domain is stronger than in
pixel one.  
	The only advantage of sample domain spatial prediction I can see
is the arithmetic precision. Indeed, in pixel domain all predictors are
8-bits width, while in frequency plane the predictors are 12 bits. 
	Where I can achieve Q15-E-17 and Q15-F-11 proposals. Could you
send me a link to these documents.
	Regards, Shevach
	Broadcom
________________________________
	From: Gary Sullivan [mailto:garysull windows.microsoft.com] 
	Sent: Monday, August 27, 2023 5:46 PM
	To: Shevach Riabtsev; mp4-tech lists.mpegif.org
	Subject: RE: Why spatial prediction in AVC performed in pixel
domain?
	Have you actually done any experiments to confirm your belief
that the frequency domain works better on noisy material?
	Of course, also, not all material is noisy...
	Gisle Bjontegaard proposed the basic concept of the spatial
prediction as part of his original proposals in 1998 for the H.26L
project (Q15-E-17 in July and Q15-F-11 in November).  I believe he had
been playing with such concepts before that as well.  I'm rather
confident that he would not have proposed such a thing unless it was
ordinarily beneficial to compression capability.
	Best Regards,
	Gary Sullivan
________________________________
		From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Shevach Riabtsev
		Sent: Monday, August 27, 2023 4:51 AM
		To: mp4-tech lists.mpegif.org
		Subject: [Mp4-tech] Why spatial prediction in AVC
performed in pixel domain?
		Dear experts
		The spatial prediction in AVC is executed in pixel
(sample) domain, while in MPEG2 and MPEG4 the spatial prediction
(actually partial prediction) is performed in frequency domain. 
		I think that on noisy material it is beneficial to
perform the spatial prediction in frequency domain in the same manner as
pixel-domain prediction. 
		Say, for each 4x4 block, DCT and quantization is
performed, then the prediction direction and the residual between
quantization coefficients of the current 4x4 block and the neighboring
(left and/or top) is calculated. 
		What was a reason to prefer the sample domain for the
spatial prediction instead of frequency one. 
		 Regards,  Shevach
		Broadcom
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