Method and apparatus for coding of intra prediction mode
Embodiments according to the present invention configure the intra prediction mode candidates into multi-level MPM sets, which comprise at least a first-level MPM set and a second-level MPM set. Encoding or decoding a current intra prediction mode is based on the multi-level MPM sets, where one syntax element of the syntax information to be generated or decoded respectively is associated with evaluating the current intra prediction mode using the first-level MPM set. A method and apparatus for chroma intra prediction mode encoding and decoding are also disclosed. The chroma intra prediction mode set includes a Luma-based chroma prediction Mode (LM), a Direct Mode (DM) and four other modes. The codeword set comprises variable-length codewords and fixed-length codewords, and the fixed-length codewords are longer than the variable-length codewords. The variable-length codewords are used for the DM and LM, and the fixed-length codewords are used for the four other modes.
1. A method for intra prediction mode decoding based on multi-level most probable mode (MPM) sets comprising a first-level MPM set and second-level MPM set, the method comprising:
determining a plurality of MPM candidates for the first-level MPM set, wherein determining the plurality of MPM candidates comprises:
identifying a first MPM candidate based on a mode of a first block; and
identifying a second MPM candidate based on a mode of a second block;
determining a plurality of most probable remaining mode (MPRM) candidates for the second-level MPM set, wherein determining the plurality of MPRM candidates comprises:
identifying a first MPRM candidate and a second MPRM candidate where the first MPRM candidate and the second MPRM candidate are different from any MPM candidate in the first-level MPM set; and
decoding syntax information related to a current intra prediction mode corresponding to a third block according to the multi-level MPM sets using a decoder, wherein one syntax element of the syntax information to be decoded is associated with a first MPM flag, wherein decoding the syntax information comprises:
determining the current intra prediction mode using the multi-level MPM sets and the first MPM flag; and
decoding the third block based on the determined current intra prediction mode.
2. The method of claim 1 , further comprising removing redundant candidates in the multi-level MPM sets.
3. The method of claim 1 , wherein DC mode and Planar mode have different mode indices in at least one of the multi-level MPM sets.
4. The method of claim 1 , wherein the first MPM flag indicates whether the current intra prediction mode is equal to any candidate in the multi-level MPM sets.
5. The method of claim 1 , wherein a remaining mode index is decoded if the first MPM flag indicates that the current intra prediction mode is not equal to any candidate in the multi-level MPM sets.
6. The method of claim 5 , wherein if a portion of remaining mode index bins or bits can be derived from already decoded bins or bits of the remaining mode index, the portion is skipped without parsing.
7. The method of claim 4 , wherein the syntax information includes a second MPM flag to indicate whether the current intra prediction mode is equal to any candidate in the first-level MPM set.
8. The method of claim 7 , wherein if the second MPM flag indicates that the current intra prediction mode is equal to one candidate in the first-level MPM set, decoding syntax information associated with MPM flags is stopped, otherwise, decoding syntax information associated with a third MPM flag to indicate whether the current intra prediction mode is equal to one candidate in the second-level MPM set is performed.
9. The method of claim 1 , wherein the syntax information includes an MPM index to indicate which of the plurality of MPM candidates in the first-level MPM set is equal to the current intra prediction mode.
10. The method of claim 9 , wherein decoding the syntax information corresponding to the MPM index is skipped if the first-level MPM set includes only one MPM candidate.
11. The method of claim 1 , wherein modes equal to the first MPM candidate or the second MPM candidate are removed from the plurality of MPRM candidates.
12. The method of claim 1 , wherein the first MPM flag indicates whether the current intra prediction mode is equal to any MPM candidate in the first-level MPM set.
13. The method of claim 12 , wherein, if the first MPM flag indicates that the current intra prediction mode is equal to one candidate in the first-level MPM set, decoding syntax information associated with MPM flags is stopped, otherwise, decoding syntax information associated with a second MPM flag to indicate whether the current intra prediction mode is equal to a candidate in the second-level MPM set is performed.
14. The method of claim 13 , wherein the syntax information includes an MPM index to indicate which of the candidates in one MPM set of the multi-level MPM sets is equal to the current intra prediction mode.
15. The method of claim 14 , wherein said decoding the syntax information corresponding to the MPM index is skipped if the one MPM set includes only one MPM candidate.
16. The method of claim 13 , wherein the syntax information includes an index of remaining mode if the second MPM flag indicates that the current intra prediction mode does not exist in the second-level MPM set of the multi-level MPM sets.
17. The method of claim 16 , wherein if a portion of remaining mode index bins or bits can be derived from already decoded bins or bits of the remaining mode index, the portion is skipped without parsing.
18. A method for intra prediction mode coding using multi-level most probable mode (MPM) sets comprising a first-level MPM set and a second-level MPM set, the method comprising:
receiving a current intra prediction mode corresponding to a first block;
determining a plurality of MPM candidates for the first-level MPM set, wherein determining the plurality of MPM candidates comprises:
identifying a first MPM candidate based on a mode of a second block; and
identifying a second MPM candidate based on a mode of a third block;
determining a plurality of most probable remaining mode (MPRM) candidates for the second-level MPM set, wherein determining the plurality of MPRM candidates comprises:
identifying a first MPRM candidate and a second MPRM candidate where the first MPRM candidate and the second MPRM candidate are different from any MPM candidate in the first-level MPM set; and
encoding the current intra prediction mode according to the multi-level MPM sets to generate syntax information using an encoder, wherein one syntax element of the syntax information generated is associated with a MPM flag, wherein encoding the current intra prediction mode comprises:
setting the MPM flag responsive to the current intra prediction mode being equal to one candidate in the multi-level MPM sets; and
encoding the first block based on the current intra prediction mode.
19. The method of claim 18 , further comprising removing redundant candidates from the multi-level MPM sets.
20. The method of claim 18 , wherein DC mode and Planar mode have different mode indices in at least one of the multi-level MPM sets.
21. The method of claim 18 , wherein the MPM flag indicates whether the current intra prediction mode is equal to any candidate in the multi-level MPM sets.
22. The method of claim 18 , wherein modes equal to the first MPM candidate or the second MPM candidate are removed from the plurality of MPRM candidates.
23. The method of claim 1 , wherein an index of the plurality of MPRM candidates is represented by a truncated unary code.
24. The method of claim 18 , wherein an index of the plurality of MPRM candidates is represented by a truncated unary code.
25. The method of claim 18 , wherein the MPM flag indicates whether the current intra prediction mode is equal to any candidate in the first-level MPM set.