JVET-AM0089 On CICP TuC for monochrome content [J. Boyce, M. M. Hannuksela (Nokia), A. Tourapis, D. Podborski (Apple)]

Several modifications are proposed to the CICP TuC in JVET-AH1005 related to monochrome content, as summarized below:

1. Add a ColourPrimaries codepoint table entry 128 for Monochrome unspecified, and renumber entries 128-129 to 129-130

2. Add a HasColourCoordinates variable to the interpretation of the ColourPrimaries codepoint value

3. Modify MatrixCoefficients codepoint table entries 19 and 20 so that the order of colour components is GBR/YZX rather than GRB/YXZ

4. Provide equations to derive Y, Cb, and Cr values for ColourPrimaries codepoint values 128 to 130 and MatrixCoefficients codepoint values 18 to 23

5. Editorial changes

It is also proposed to output a CICP version 5 working draft at this meeting based on the attached specification text.

For the first aspect, the motivation is that unspecified logically comes before a variety of specified values.

For the second aspect, it was discussed that instead of a variable flag HasColourCoordinates, this could be extended to an idc value, e.g. indicating that additional information is necessary to interpret a depth map. For the scope of the current proposal, this is not necessary.

For the third aspect, the motivation is that GBR is more commonly used than GRB (logical order)

For the fourth aspect, also matrix coefficients would be used for unspecified, alpha and depth, when carried in the monochromatic picture. The update in version 2 of the document clarifies that this can only be used in combination with matrix coefficient types 18, 19 and 20. It was commented that the equations 88-92 are not actually needed for depth maps and alpha carried in the Y component, but the bitstream should contain information how to interpret them, e.g. by SEI message. Further study may be necessary to clarify how this SEI message could be made available, as currently SEI messages relating to alpha or depth can only be used and associated with auxiliary layers. An informal note should be added that some external means would be necessary to interpret the usage of the values 128-130. A draft of such a note was provided in v3 of JVET-AM0089 and reviewed Wed. 2 July afternoon. The note was agreed to be appropriate.

Aspects 1-3 as well as fifth aspect (editorial) should be agreeable