id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
859	JVET-Q0089 - TS residual coding disabled with dependent quantization	bheng		"There appears to be a mismatch between the SW and draft text for the case of:

    slice_ts_residual_coding_disabled_flag=1 
    ph_dep_quant_enabled_flag = 1

It's not immediately clear which aspects of dependent quantization are intended to apply in Q0089 for a transform-skip coded TU.  I believe the current behavior is as follows.

  - Both the text and the software use dependent quantization state for CABAC context determination. But they don't actually use dependent quantization during the actual dequant process.

  - For dequant, the SW does not use dependent quantization at all for transform skip TUs.  The DepQuant code is bypassed here:

    if ( tu.cs->picHeader->getDepQuantEnabledFlag() && (tu.mtsIdx[compID] != MTS_SKIP) )


  - For dequant, the draft text seems to apply the 2x shift for dependent quantization (from the syntax table - shown below), but not any of the other aspects (e.g. in 8.7.3):

    TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] = 
     ( 2 * AbsLevel[ xC ][ yC ] − ( QState > 1 ? 1 : 0 ) ) *
     ( 1 − 2 * coeff_sign_flag[ n ] )


At a minimum, I guess the text needs to remove the 2x shift above for the case of transform_skip_flag = 1.  

Additionally, it's not really clear if the residual coding was supposed to use '''any''' of the dependent quantization state for these transform skip TUs (e.g. why does dependent quant state affect CABAC context if dependent quantization is not used). Or if all of the dependent quantization aspects were supposed to be disabled for transform skip TUs.  So additional changes might be necessary in both text and SW.



"	defect	closed	minor		spec	VVC D8 vB	fixed		ksuehring bbross XiangLi fbossen jvet@…