| JCTVC-M0127 AHG5: Unified intra prediction angles for 4:2:2 chroma format [H. Nakamura, M. Ueda, S. Fukushima, T. Kumakura (JVC Kenwood)]
(Discussion chaired by D. Flynn.)
In the current draft of HEVC Range Extensions and the test model HM-10.0-RExt-2.0, some additional intra prediction angles for 4:2:2 chroma are calculated from intra prediction angle for luma and 4:2:0/4:4:4 chroma. This contribution proposes the unification of chroma intra prediction angles between 4:2:2 chroma and the others without adding any intra prediction angles for 4:2:2 chroma.
The derivation of the intra prediction angle in 4:2:2 introduces new angles that are not present in the 4:2:0/4:4:4 design which may not have been fully appreciated at the time. This results in an implementation burden to handle the extra angles and additionally causes the MDCS derivation to not correctly account for the actual chroma angle since the decision is based upon the mode index and not the derived angle.
Options: A) use a mapping table, provides less than 0.1% all-intra coding gain, B) allow MDCS to take account of the chroma angle, provides 0.1% all-intra coding gain.
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