JVET-S0228 Transform coefficients range extension for high bit-depth [T. Zhou, T. Chujoh, E. Sasaki, T. Ikai (Sharp)]
This contribution was discussed together with those in section 5, but the notes were moved here since it is beyond the scope of VVC v1.
This contribution proposes a format range extension design for high bit depth coding. In HEVC format range extension (RExt), the extended precision flag (extended_precision_processing_flag) is specified. When extended precision flag is equal to 1, it extends the transform coefficient range from 15 bit to BitDepth + 6 bit and modifies a bdShift value from 20 – BitDepth to 11. However, this extended precision flag was only supported in 16 bit profiles (Monochrome 16, Main 4:4:4 16 Intra, and Main 4:4:4 16 Still Picture) and variables in 10 bit case are also changed according to the flag. This contribution proposes to use BitDepth + 5 and bdShift to 10 in the range of 10 to 16 bit case in VVC. It is reported that high precision design provides better coding performance compared with the current bit depth precision in 12, 14 bit case as well as 16 bit case.Discuss with parent bodies as possible v2 item. Requires requirement study and studying the need for it – including the question if VVC is an attractive alternative to HEVC in this area.
It was agreed to set up an AHG to study potential need for alignments of tools, benefit of VVC tools for high bit rate sequences, testing conditions for higher bit depth, native higher bit depth sequences, etc.
It was pointed out that this could also be highly relevant for future HDR solutions.