Incorrect clipping for high dynamic range mastering display color volume metadata

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
82/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
cpp

Research direction

Open _studio/mfx_lib/encode_hw/av1/agnostic/base/av1ehw_base_hdr.cpp around lines 42-57 and inspect the clipping of primary_chromaticity/display_primaries values, especially DisplayPrimariesY. Compare the upper bound with the AV1 and referenced AVC/HEVC/VVC specifications. Done means primary_chromaticity_y can reach 0.840000 and DisplayPrimariesY has an upper limit of at least 55050.

Written by the indexing model from the issue text.

Description

https://github.com/intel/vpl-gpu-rt/blob/e6a12d5090489e89a8f6dda8ff2842c734ceec54/_studio/mfx_lib/encode_hw/av1/agnostic/base/av1ehw_base_hdr.cpp#L42-L57

The implemented clipping of primary_chromaticity/display_primaries parameters is incorrect as it limits primary_chromaticity_y to the value of 0.762940, but it must be the 0.840000 (according to the range derived from AVC/HEVC/VVC specs).
To meet this requirement the upper limit of DisplayPrimariesY must be at least 55050.

Related specs:
https://aomediacodec.github.io/av1-spec/#metadata-high-dynamic-range-mastering-display-color-volume-semantics
D.2.29 of Rec. ITU-T H.264 (V15) (08/2024), dl link

BTW, AV1 specification does not set limits for HDR MDCV values (other than those determined by syntax).

Dominant language
C++
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