Mismatch between SW and spec on CG size for TS Chroma

[wzeng]

In VVC D7 vB, coding group size for chroma residual_ts_coding is set to 2x2 in case of Nx2 chroma block as indicated below:

log2SbSize = ( Min( log2TbWidth, log2TbHeight ) < 2 ? 1 : 2)

But in VTM7.0rc1, coding group size in such case is set to 8x2, aligned with regular residual coding case.

So it's suggested to align the spec text with VTM.

[bbross]

Thanks for reporting! I will it it in JVET-P2001-vC by introducing log2SbW and logSbH as for the regular coding case as follows:

log2SbW = ( Min( log2TbWidth, log2TbHeight ) < 2 ? 1 : 2 )
log2SbH = log2SbW
if( log2TbWidth + log2TbHeight > 3 ) {

if( log2TbWidth < 2 ) {

log2SbW = log2TbWidth
log2SbH = 4 − log2SbW

} else if( log2TbHeight < 2 ) {

log2SbH = log2TbHeight
log2SbW = 4 − log2SbH

}

}
numSbCoeff = 1 << ( log2SbW + log2SbH )
lastSubBlock = ( 1 << ( log2TbWidth + log2TbHeight − ( log2SbW + log2SbH ) ) ) − 1

and all occurrences of

xS = DiagScanOrder[ log2TbWidth − log2SbW ][ log2TbHeight − log2SbH ][ i ][ 0 ]
yS = DiagScanOrder[ log2TbWidth − log2SbW ][ log2TbHeight − log2SbH ][ i ][ 1 ]

and

xC = ( xS << log2SbW ) + DiagScanOrder[ log2SbW ][ log2SbH ][ n ][ 0 ]
yC = ( yS << log2SbH ) + DiagScanOrder[ log2SbW ][ log2SbH ][ n ][ 1 ]