JVET-AM0108 AHG9: On colour mapping information SEI message [J. Samuelsson-Allendes, S. Deshpande (Sharp)]

Colour Mapping Information (CMI) SEI message is a new SEI message included in the Technologies under Consideration (TuC) document for VSEI (JVET-AL2032). The CMI SEI message provides information to enable colour mapping of decoded picture luma samples to RGB samples. In the current version of the CMI SEI message, a piecewise linear mapping function can be signalled. It is asserted that this works well for mapping functions such as “Jet” but it is asserted that this is inefficient for smooth continuous mapping functions such as “Turbo” and “Viridis”. This contribution proposes the following changes to the CMI SEI message:

1. Add an alternative signalling method using fixed point polynomial coefficients
2. Add the possibility of signalling a text string to identify the intended colour mapping function
3. Use minus1 signalling for the anchor point delta when signalled with uniform spacing
4. Make the following minor edits to the existing semantics:
   1. Fix the semantics of cmi_num_bits_minus8 to use correct names of other syntax elements
   2. Add a constraint that anchor points are signalled in increasing order
   3. Remove leftover sentence referring to ColourMap codepoint in CICP
   4. Add missing cmi_ prefix to colour_map_id
   5. Remove hanging "if( a >= 0 )"
   6. Add handling of when decSample <= cmi_anchor_point_x[ 0 ]
   7. Remove the [c] part for cmi_anchor_point_x

Version 2 of the contribution includes a few minor fixes compared to the first version of the contribution.

It was suggested that 32 bits per coefficient may be too high. It was suggested to include a flag to switch between 16 and 32 bits.

It was suggested to rename the SEI message colour map SEI.

Agreed to add item 1.

It was suggested that same common maps could be predefined in a table. This is a possible alternative to item 2.

It was suggested that if a text string was added, a language tag may be added.

It was suggested that the semantic of cmi_colour_map_name should avoid including “function intended to be applied to the decoded picture.”

Agreed to add item 2, item 3, item 4.

Additional SEI message aspects (6)

Contributions in this area were discussed during 1820–2000 on Sunday 29 June 2025 and 1400–1545 on Monday 30 June 2025 (chaired by J. Boyce).

JVET-AM0108 AHG9: On colour mapping information SEI message

Referred to editors for consideration: