[M4IF Technotes] CBPC and CBPY

[Chandra Sekhar Reddy G]

hi,
whether dc-coeff (ofcourse diff-dc) to be coded independently or along with
ac-coeff is dependent on intra-dc-vlc-thr and quant.
if ac-prediction is used, then the block, with only top-row-coeff or only
first-column-coef, *may* become all-zero after ac-prediction.
for that block, cbp will be 0.
but on the decoder side, an all-zero block (cbp is 0 for that block), may
get some coeff after ac/dc-pred, which will go through IQ and IDCT.
regards,
chandra
----- Original Message -----
From: "Herbert Thoma" <tma   iis.fhg.de>
To: "Bart Lehane" <lehaneb   eeng.dcu.ie>
Cc: <technotes   lists.m4if.org>
Sent: Wednesday, March 26, 2024 8:45 PM
Subject: Re: [M4IF Technotes] CBPC and CBPY
> Bart Lehane schrieb:
> >
> > Hello,
> >
> > In a rectangular I frame, is it possible to have values of cbpy (coded
> > block pattern for luminance) that do not equal '1111', or values of cbpc
> > (cbp for chrominance) that do not equal '11'??
> >
> > If true, would this give a pattern code not equal to '111111' which
> > would mean that there would be no DCT coefficients for a particular
> > block?? (i.e if pattern_code[5] = 0, then the second chrominance block
> > would have no dct coefficients)
> >
> > First of all is this scenario possible, where an intra macroblock
> > contains a block with no (AC) DCT coefficients? If it is possible, what
> > values would go into that block?
>
> In an I frame the DC coefficient is not regarded when computing cbp.
> The DC coefficient is allways present and transmitted. If the pattern
> code for a particular block is 0 then only the DC coefficient is present
> and all pixels of that block get the same value according to the
> DC coefficient.
>
> Regards,
>  Herbert.
>
> > Thanks in advance,
> >
> > Bart
> >
> > _______________________________________________
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>
> --
> Herbert Thoma
> FhG-IIS A, Studio Department
> Am Wolfsmantel 33, 91058 Erlangen, Germany
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