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25th Meeting: by teleconference, January 2022 2022-01-04 00:30
AHG2/AHG8: On the range extensions GCI flags
Authors: Ye-Kui Wang ByteDance
Abstract
When gci_present_flag is equal to 0, no GCI syntax elements exist, including the new range extensions GCI flags. In that case, the general_constraint_info( ) syntax structure does not impose any constraint. However, when gci_present_flag is equal to 1, although all the GCI syntax elements specified in VVC edition 1 are surely present, the newly added range extensions GCI flags may or may not be present, depending on whether gci_num_additional_bits (which was gci_num_reserved_bits in VVC edition 1) is greater than 0.
Meeting Notes
JVET-Y0049 AHG2/AHG8: On the range extensions GCI flags [Y.-K. Wang (Bytedance)]

When gci_present_flag is equal to 0, no GCI syntax elements exist, including the new range extensions GCI flags. In that case, the general_constraint_info( ) syntax structure does not impose any constraint. However, when gci_present_flag is equal to 1, although all the GCI syntax elements specified in VVC edition 1 are surely present, the newly added range extensions GCI flags may or may not be present, depending on whether gci_num_additional_bits (which was gci_num_reserved_bits in VVC edition 1) is greater than 0.

An asserted problem arises when gci_present_flag is equal to 1 and gci_num_additional_bits is equal to 0, in which case the new range extensions GCI flags are not present while their values are not inferred, and thus it is unclear whether the constraints specified by the flags equal to 1 apply or not.

To address the above asserted problem, this contribution proposes to specify that the value of each of the six newly added GCI flags (listed below) is inferred to be equal to 0 when gci_present_flag is equal to 1 and gci_num_additional_bits is equal to 0:

  1. gci_all_rap_pictures_constraint_flag
  2. gci_no_extended_precision_processing_constraint_flag
  3. gci_no_ts_residual_coding_rice_constraint_flag
  4. gci_no_rrc_rice_extension_constraint_flag
  5. gci_no_persistent_rice_adaptation_constraint_flag
  6. gci_no_reverse_last_sig_coeff_constraint_flag

Additionally, some asserted editorial improvement changes are proposed to the semantics of gci_present_flag, gci_sixteen_minus_max_bitdepth_constraint_idc, and gci_three_minus_max_chroma‌_format_constraint_idc.

See further notes under JVET-Y0190.

It was pointed out that another option would be to globally define that whenever a specific GCI flag is not present, its value would be inferred to be zero. This would avoid that the problem happens again in future extensions and would not be specific to range extensions.

JVET-Y0049 AHG2/AHG8: On the range extensions GCI flags [Y.-K. Wang (Bytedance)]

See section 4.2.

References:
JVET-X2005
Cited:
JVET-Y0002 JVET-Y0008 JVET-Y0237 JVET-Y0242
PATENTS:
20240305831 1.00 WO/2023/092019 0.95 WO/2023/137477 0.90 20240373068 0.85 4325850 0.80 20230128218 0.75 202227074501 0.70 20230097856 0.65
ARCHIVE v1 :
JVET-Y0049-v1.docx
Decisions
It was pointed out that another option would be to globally define that whenever a specific GCI flag is not present, its value would be inferred to be zero. This would avoid that the problem happens again in future extensions and would not be specific to range extensions.
See section 4.2.
Citation