id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
1648	[misalignment] on use of sps_chroma_horizontal/vertical_collocated_flag	hmjang		"SPEC subclause 8.5.6.3.1

sps level chroma phase information is used to derive pixel position inside of reference picture for motion compensation.
during this process, it is written that information is from SPS which current picture refer to. 

addX = sps_chroma_horizontal_collocated_flag ? 0 : 8 * ( scalingRatio[ 0 ] − ( 1  <<  14 ) )	(903)
addY = sps_chroma_vertical_collocated_flag ? 0 : 8 * ( scalingRatio[ 1 ] − ( 1  <<  14 ) )	(904)



but in the VTM, those information is from SPS which reference picture is refer to.
int addX =   isLuma(compID) ? 0 : int(1 - refPic->cs->sps->getHorCollocatedChromaFlag()) * 8 * (scalingRatio.x - SCALE_1X.x);
int addY =   isLuma(compID) ? 0 : int(1 - refPic->cs->sps->getVerCollocatedChromaFlag()) * 8 * (scalingRatio.y - SCALE_1X.y);

in case of single layer, SPS information is same between reference picture and current picture but in the multilayer case, each CLVS can refer own SPS. it means those information can be different between reference picture and current picture.


so VTM should be fixed to use it from current picture's SPS.



"	defect	new	major		VTM				ksuehring XiangLi fbossen jvet@…