JVET-S0172 AHG9: On generalized cubemap projection SEI message [Y.-H. Lee, J.-L. Lin, Y.-J. Chen, C.-C. Ju (MediaTek)]
This contribution was discussed in the HLS AHG pre-meeting at 1900 on 20 June.
This proposes the following modifications and constraints related to the generalized cubemap projection SEI message:
- Add a condition check of gcmp_guard_band_flag when deriving gcmpGuardBandSamples to prevent from accessing an uninitialized variable.
- Add constraints on gcmp_face_index[ i ] and gcmp_face_rotation[ i ] for the hemisphere cubemap projection to guarantee that the four half faces are the ones connecting to the full face and can represent 180°×180° omnidirectional image/video. (The “if” part of the “otherwise” should be removed.)
- Include an offset the remapping of sample locations on the half faces of the hemisphere cubemap projection.
AHG Recommendation (bug fix and sensibility constraints): Adopt.
It was asked whether each half-height / half-width is required to be an integer multiple of 2 in the 4:2:0 / 4:2:2 cases, to avoid half-chroma samples.
Offline work by the proponent was requested to establish this constraint.
This was further discussed in the main JVET meeting at 1430 on 25 June (chaired by GJS).
A -v2 version of the contribution was provided that includes the requested constraint. It was commented that although the spirit of the constraint is clear in the provided text, it may be better to derive specific variables and constrain their values rather than to use verbal expressions such as “the width of each face”.
Editor action item: The contributor and editor were asked to consider the above suggestion in the text finalization.