Using refMvLX in sample interpolation process

[Vadim]

In the section 8.5.6.3.1 General of 8.5.6.3 Fractional sample interpolation process, for luma interpolation refMvLX is used, while chroma uses mvLX, where mvLX = refMvLX − mvOffset.
It seems that refMvLX should be used in both cases.

A typo in equation (8-769)
xFracC = refyC & 31, it should be xFracC = refxC & 31

[hanhuang]

It looks like the following is not necessary, and mvOffset can be removed from the input.
"The motion vector mvLX is set equal to ( refMvLX − mvOffset )."
The reference sample padding should use the refMvLX instead of mvLX.

[bbross]

Thanks for brining that up.
Can someone confirm that in "8.5.6.3.1 General", mvLX needs to be replaced by refMvLX and mvOffset can be removed from the input of this process?

[jlchen]

mvLX (equal to refMvLX - mvOffset) can not be removed since the original MV is used to identify the bounding block boundaries for DMVR padding process.

[bbross]

Ok thanks. Jianle and I kept mvOffset and just replaced mvLX with refMcLX where necessary.

This will be fixed JVET-P2001-vC.

[Vadim]

Would it be possible to double check whether refMvLX should be used for chroma or refMvCLX? It is probably correct for 4:2:0, but maybe not for other formats. Coordinate range is the same as luma in that cases, but shift is larger by 1.

refMvCLX[ 0 ] = refMvLX [ 0 ] * 2 / SubWidthC
refMvCLX[ 1 ] = refMvLX[ 1 ] * 2 / SubHeightC

Same for bounding block, where mvLX is always used, maybe it should be mvCLX too.

[jlchen]

Vadim,

I think you're right. refMvCLX and mvCLX should be used, instead of refMvLX and mvLX, for chroma components to make non-420 correct.

[Vadim]

Thank you for checking it.