[Mp4-tech] Non zero Coefficients in deblocking filter

[Jain, Anurag]

Gary,
Doesn't CBP come at 8x8 block level and Total Coefficients come at 4x4
sub-block level. Boundary strength is calculated for sub-block edges so
Total Coefficients is a more appropriate measure to check. Hence CBP bit
can be non-zero and still some of the sub-blocks may have all-zero
coefficients.
I think we need to check Total Coefficients and derive CSBP (Coded
Sub-Block Pattern) for loop filtering.
Regards,
Anurag
________________________________
From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Gary Sullivan
Sent: Tuesday, April 22, 2024 9:28 AM
To: Srikar Dasari; mp4-tech lists.mpegif.org
Subject: RE: [Mp4-tech] Non zero Coefficients in deblocking filter
Srikar,
I suggest to check what the reference software is doing.  If I remember
correctly, the text is phrased so that certain things are prohibited (by
disallowing the values of all transform coefficients being decoded as
zero when some coded block pattern bits are set), so that the complexity
of the decoding process is minimized.  The text and software do the same
thing, but that is not obvious at first glance, because their
equivalence depends on the exact phrasing of the text.  We had one or
two correction efforts devoted to this topic in the past, so if you look
in some old drafts you will find incorrect text.
Again, my basic advice is to check what you find in the JM reference
software.  
Best Regards,
Gary Sullivan
________________________________
From: mp4-tech-bounces lists.mpegif.org
[mp4-tech-bounces lists.mpegif.org] On Behalf Of Srikar Dasari
[srikar pelican-networks.com]
Sent: Monday, April 21, 2024 3:43 PM
To: mp4-tech lists.mpegif.org
Subject: [Mp4-tech] Non zero Coefficients in deblocking filter
Experts,
I have a question in the boundary calculation in deblocking filter. I
kinda of asked this question earlier. I need some more clarification. 
In the filtering process the boundary strength is set based on one of
the conditions being, the luma block p0 or luma block q0 contains
non-zero transform coefficient levels.
My question is, 
Isn't this non-zero transform coefficient level condition, come from
both CBP value and also from the TC (total coefficients) during the
CAVLC decoding?
In other words, Do we have to consider the CBP pattern alone or Do we
have to take into account TC being zero, in addition to CBP. 
Please let me know, if I am not clear anywhere. Your answers are greatly
appreciated.
Thanks,
Srikar
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