Unclear variables in 9.3.4.2.2 for split_cu_flag

[peterderivaz]

The derivation process of ctxInc for split_cu_flag uses cIdx (as part of availability calculations) and chType (in table 133).

However, neither cIdx nor chType are defined in 7.3.11.4 coding tree syntax.

What values should be used for cIdx and chType in this case?

[bbross]

Valid point. Since the different syntax elements are parsed on different levels, different input parameters have to be defined for syntax elements at different syntax structure levels. Will clarify that including how chType and cIdx are derived for the case of split_cu_flag.
The fix will be included in JVET-W1004-v2.

[bbross]

Separated the input as follows:

For the syntax elements alf_ctb_flag[ cIdx ][ ctbX ][ ctbY ], alf_ctb_cc_cb_idc[ ctbX ][ ctbY ], and alf_ctb_cc_cr_idc[ ctbX ][ ctbY ], input to this process is the luma location ( x0, y0 ) set equal to ( xCtb, yCtb) specifying the top-left luma sample of the current coding tree unit relative to the top-left sample of the current picture, the colour component cIdx for alf_ctb_flag[ cIdx ][ ctbX ][ ctbY ], cIdx equal to 1 for alf_ctb_cc_cr_idc[ ctbX ][ ctbY ] and cIdx equal to 2 for alf_ctb_cc_cr_idc[ ctbX ][ ctbY ]. The location ( ctbX, ctbY ) is set equal to ( x0 >> CtbLog2SizeY, y0 >> CtbLog2SizeY ), the location ( ctbAx, ctbAy ) is set equal to ( x0 >> CtbLog2SizeY, ( y0 − 1 ) >> CtbLog2SizeY ), and the location ( ctbLx, ctbLy ) is set equal to ( ( x0 − 1 ) >> CtbLog2SizeY, y0 >> CtbLog2SizeY ).

For the syntax elements split_qt_flag, split_cu_flag, and non_inter_flag, input to this process is the luma location ( x0, y0 ) specifying the top-left luma sample of the current luma block relative to the top-left sample of the current picture, the current coding quadtree depth cqtDepth for split_qt_flag, the width and the height of the current coding block in luma samples cbWidth and cbHeight, and the variables allowSplitBtVer, allowSplitBtHor, allowSplitTtVer, allowSplitTtHor, and allowSplitQt as derived in the coding tree semantics in clause 7.4.12.4 for split_cu_flag. The dual tree channel type chType is set equal to 1 if the variable treeType in the associated coding tree syntax is equal to DUAL_TREE_CHROMA, and set equal to 0 otherwise. The colour component cIdx is set equal to chType.

For the syntax elements cu_skip_flag[ x0 ][ y0 ], pred_mode_flag[ x0 ][ y0 ], pred_mode_ibc_flag[ x0 ][ y0 ], intra_mip_flag, inter_affine_flag[ x0 ][ y0 ] and merge_subblock_flag[ x0 ][ y0 ], input to this process is the luma location ( x0, y0 ) specifying the top-left luma sample of the current luma block relative to the top-left sample of the current picture, and the dual tree channel type chType for pred_mode_flag[ x0 ][ y0 ] and pred_mode_ibc_flag[ x0 ][ y0 ]. The colour component cIdx is set equal to chType.

[yk]

Thanks! This has been fixed in JVET-W1004-v2.