id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
572	Incorrect use of chroma distortion weights if Cb and Cr QP offsets differ (affects perceptual QPA, may affect SBT in HDR-PQ CTCs)	crhelmrich		"VTM 6.x, in ''initEncSlice()'', calls ''setUpLambda()'' to initialize the Cb and Cr distortion weights. These weights are computed, and multiplied onto the respective component distortions in ''RdCost::getDistPart()'', independently for Cb and Cr. However, there are some places where an '''average chroma weight''' is calculated via ''RdCost::getChromaWeight()'' and used for both Cb and Cr. This does not seem to be an issue with the SDR or HDR-HLG CTCs, but if I understand correctly, different Cb and Cr QP offsets (and, thus, different Cb and Cr lambdas) may occur in the HDR-PQ CTCs.

Therefore, in the case of unequal Cb and Cr QP offsets, the following encoder functions may, according to my understanding, work suboptimally:

* rate control (if pCfg->getUseRateCtrl() in ''encodeCtus()'', not sure if this is used)
* perceptual QPA with chroma QP adaptation (e.g., if pCfg->getUsePerceptQPA() && pcSlice->getPPS()->getUseDQP() in ''encodeCtus()'')
* SBT fast algorithm (''InterSearch::calcMinDistSbt()'' called in ''xEncodeInterResidual()'').

Before I submit a merge request with a proposed fix (used of a RdCost::getDistortionWeight('''compID''') instead of the RdCost::getChromaWeight() at the respective places), it would be great if someone could confirm that my understanding is correct.

Thanks and best,

Christian
"	defect	new	major		VTM	VTM-6.1			ksuehring XiangLi fbossen jvet@…