id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
1632	Incorrect indexing used for choosing matrix intra sample prediction	peterderivaz		"Clause 8.4.5.2.1 reads:

{{{
Inputs to this process are:
– a sample location ( xTbCmp, yTbCmp ) specifying the top-left sample of the current transform block relative to the 
top-left sample of the current picture,
...
if MipChromaDirectFlag[ xTbCmp ][ yTbCmp ] is equal to 1 and cIdx is not equal to 0, 
}}}

This looks up values in MipChromaDirectFlag based on counts of chroma samples.

However, when MipChromaDirectFlag is derived, the indexing is done based on counts of luma samples:
{{{
 Derivation process for chroma intra prediction mode
Input to this process are:
– a luma location ( xCb, yCb ) specifying the top-left sample of the current chroma coding block
  relative to the top-left luma sample of the current picture,
...
In this process, the chroma intra prediction mode IntraPredModeC[ xCb ][ yCb ] and the MIP chroma direct mode flag 
MipChromaDirectFlag[ xCb ][ yCb ] are derived.
}}}

I think this can be fixed by changing 8.4.5.2.1 to use ""MipChromaDirectFlag[ xTbCmp * SubWidthC ][ yTbCmp * SubHeightC ]"" instead of ""MipChromaDirectFlag[ xTbCmp ][ yTbCmp ]""."	defect	closed	minor	H.266/VVC v4	spec	H.266/VVC v3	fixed		ksuehring bbross XiangLi fbossen jvet@…