id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
85	Spec issues related to MTS	jason		"'''1) Mismatch between draft 2 and VTM/BMS-2.0.1'''
According to the MTS scheme adopted in the last meeting and VTM/BMS-2.0.1, when intra predicted block has less than 3 non-zero coefficients and cu_mts_flag[ x0 ][ y0 ] is equal to 1, DST-VII is applied both horizontally and vertically. (mts_idx is not signalled)
However, in 7.4.5.8, mts_idx[ x0 ][ y0 ] is inferred to be equal to -1, which means DCT-II is applied both horizontally and vertically for that case.

Semantics and decoding process related to this issue should be revised.

'''Simple fix:'''
In 7.4.5.8,
When mts_idx[ x0 ][ y0 ] is not present, it is inferred as follows:

If cu_mts_flag[ x0 ][ y0 ] is equal to 0, mts_idx[ x0 ][ y0 ] is inferred to be equal to -1.
Otherwise (cu_mts_flag[ x0 ][ y0 ] is equal to 1), mts_idx[ x0 ][ y0 ] is inferred to be equal to 0.

In 8.3.4.1,
The variable trTypeHor specifying the horizontal transform kernel and the variable trTypeVer specifying the vertical transform kernel are derived as follows:
If cIdx is equl to 0, trTypeHor and trTypeVer are derived in Table 8-6 depending on mts_idx[ x ][ y ] and CuPredMode[ x ][ y ].
Otherwise (cIdx is equal to 1 or 2), trTypeHor and trTypeVer are equal to 0.

Table 8-6
||=mts_idx[ x ][ y ]||=CuPredMode[x][y]==MODE_INTRA||=CuPredMode[x][y]==MODE_INTER||
|| ||=trTypeHor, trTypeVer||=trTypeHor, trTypeVer||
||=-1 (inferred)||=0, 0||=0, 0||
||=0 (00 / inferred)||=1, 1||=2, 2||
||=1 (01)||=2, 1||=1, 2||
||=2 (10)||=1, 2||=2, 1||
||=3 (11)||=2, 2||=1, 1||




'''2)Redundant condition for mts_idx in 7.3.4.8'''
When cIdx is equal to 0 (luma TB) amd cu_mts_flag[ x0 ][ y0 ] is equal to 1, transform_skip_flag[ x0 ][ y0 ][ cIdx ] is inferred to be equal to 0 according to 7.4.5.8.
Thus, checking whether the transform skip flag is equal to 0 or not can be removed in the last of 7.3.4.8

'''Simple fix:'''
In 7.3.4.8
if ( cu_mts_flag[ x0 ][ y0 ] && ( cIdx == 0 ) &&
 ( ( CuPredMode[ x0 ][ y0 ] == MODE_INTRA && numSig > 2) ||
 ( CuPredMode[ x0 ][ y0 ] == MODE_INTER ) ) )
    mts_idx[ x0 ][ y0 ]
"	defect	closed	major	VVC D2 v7	spec	VVC D2 v5	fixed		ksuehring bbross XiangLi fbossen jvet@…