Mismatch on subclause 8.4.3 (Derivation process for chroma intra prediction mode)

[hmjang]

There is a mismatch on 8.4.3.

In order to align the Spec. to SW, the specification should be changed from

In this process, the chroma intra prediction mode IntraPredModeC[ xCb ][ yCb ] is derived.
The corresponding luma intra prediction mode lumaIntraPredMode is derived as follows:
– If intra_mip_flag[ xCb ][ yCb ] is equal to 1, lumaIntraPredMode is set equal to INTRA_PLANAR.
– Otherwise, if CuPredMode[ 0 ][ xCb ][ yCb ] is equal to MODE_IBC or MODE_PLT, lumaIntraPredMode is set equal to INTRA_DC.
– Otherwise, lumaIntraPredMode is set equal to IntraPredModeY[ xCb + cbWidth / 2 ][ yCb + cbHeight / 2 ].
The chroma intra prediction mode IntraPredModeC[ xCb ][ yCb ] is derived using cclm_mode_mode_flag, cclm_mode_idx, intra_chroma_pred_mode and lumaIntraPredMode as specified in Table 8 2.

to

The corresponding luma intra prediction mode lumaIntraPredMode is derived as follows:
– If intra_mip_flag[ xCb + cbWidth / 2 xCb ][ yCb + cbHeight / 2 yCb ] is equal to 1, lumaIntraPredMode is set equal to INTRA_PLANAR.
– Otherwise, if CuPredMode[ 0 ][ xCb + cbWidth / 2 xCb ][ yCb + cbHeight / 2 yCb ] is equal to MODE_IBC or MODE_PLT, lumaIntraPredMode is set equal to INTRA_DC.
– Otherwise, lumaIntraPredMode is set equal to IntraPredModeY[ xCb + cbWidth / 2 ][ yCb + cbHeight / 2 ].
The chroma intra prediction mode IntraPredModeC[ xCb ][ yCb ] is derived using cclm_mode_mode_flag, cclm_mode_idx, intra_chroma_pred_mode and lumaIntraPredMode as specified in Table 8 2.

Additionally, one editorial suggestion could be considered.
In 8.4.2 process, intra_mip_flag[ xCb ][ yCb ] is refered. it could lead misinterpretation about its behavior. for example, DUAL_TREE_CHROMA case, intra_mip_flag is not signaled. it mean intra_mip_flag[ xCb ][ yCb ] is 0 for chroma component.

I suggest that the clear description. It could be changed that "intra_mip_flag[ xCb ][ yCb ] of the corresponding luma coding block" instead of "intra_mip_flag[ xCb ][ yCb ]".

[bbross]

Good catch! Thanks!

Fixed it in a document we are preparing to be submitted as an editorial input
to the 16th JVET meeting.