Method and apparatus for non-square intra mode coding
In a method and apparatus for predictive Intra coding of a non-square block using modified mode-dependent coefficient scanning (MDCS), the modified MDCS is derived from the MDCS that is designed for a square block. The mapped Intra modes for the non-square block are derived by mapping the Intra modes for the square block to the mapped Intra modes for the non-square block. The mapped Intra modes are divided into multiple groups including a first modified angular group and a second modified angular group. The modified MDCS modifies the number of the mapped Intra modes in the first modified angular group or the second modified angular group by comparing an angle spanned by the mapped Intra modes in the first modified angular group or the second modified angular group with the angle spanned by the corresponding Intra modes of the conventional MDCS.
1. A method for coding a block based on mode-dependent coefficient scanning (MDCS), the method comprising:
specifying a first MDCS for a plurality of Intra modes, wherein the plurality of Intra modes have mode 2 through mode 18 covers from −135 degree direction to −45 degree direction and mode 18 through mode 34 covers from −45 degree direction to +45 degree direction, wherein mode 10 corresponds to −90 degree direction and mode 26 corresponds to 0 degree direction, wherein the plurality of Intra modes are divided into multiple groups comprising a first angular group consisting of the Intra modes from mode 6 through mode 14 and a second angular group, and the first MDCS uses a vertical coefficient scanning for the first angular group and a non-vertical coefficient scanning for the second angular group;
specifying a second MDCS for a plurality of Intra modes, wherein the plurality of Intra modes are divided into multiple groups comprising a first modified angular group consisting of the Intra modes from mode 8 through mode 12 and a second modified angular group comprising more modes than the first modified angular group, wherein the angle formed by the first modified angular group is substantially the same as the angle formed by the first angular group, and the second MDCS uses the vertical coefficient scanning for the first modified angular group, and the non-vertical coefficient scanning for the second modified angular group;
receiving input data associated with a current block;
determining whether the current block corresponds to a 2N×2N block or an N×2N block, wherein N is a positive integer;
when the current block corresponds to the 2N×2N block, processing the current block according to the first MDCS, wherein the vertical coefficient scanning is applied to the current block if a current intra mode of the current block belongs to the first angular group, and the non-vertical coefficient scanning is applied to the current block if the current intra mode of the current block belongs to the second angular group; and
when the current block corresponds to the N×2N block, processing the current block according to the second MDCS, wherein the vertical coefficient scanning is applied to the current block if the current intra mode of the current block belongs to the first modified angular group, and the non-vertical coefficient scanning is applied to the current block if the current intra mode of the current block belongs to the second modified angular group wherein the second angular group consists of the Intra modes having mode 22 through mode 30; and the Intra modes in the second modified angular group is between mode 18 through mode 34.
2. The method of claim 1 , wherein the non-vertical coefficient scanning corresponds to a horizontal coefficient scanning or a diagonal coefficient scanning.
3. The method of claim 1 , wherein when the current block corresponds to the 2N×2N block, the current block is associated with a 2N×2N luma block in a picture using 4:2:2 color sub-sampling.
4. The method of claim 1 , wherein when the current block corresponds to the N×2N block, the current block is associated with a N×2N chroma block in a picture using 4:2:2 color sub-sampling.
5. The method of claim 1 , wherein N is 2 or 4.
6. An apparatus for coding a block based on mode-dependent coefficient scanning (MDCS), the apparatus comprising one or more electronic circuits configured to:
specify a first MDCS for a plurality of Intra modes, wherein the plurality of Intra modes have mode 2 through mode 18 covers from −135 degree direction to −45 degree direction and mode 18 through mode 34 covers from −45 degree direction to +45 degree direction, wherein mode 10 corresponds to −90 degree direction and mode 26 corresponds to 0 degree direction, wherein the plurality of Intra modes are divided into multiple groups comprising a first angular group consisting of the Intra modes from mode 6 through mode 14 and a second angular group, and the first MDCS uses a vertical coefficient scanning for the first angular group and a non-vertical coefficient scanning for the second angular group;
specify a second MDCS for a plurality of Intra modes, wherein the plurality of Intra modes are divided into multiple groups comprising a first modified angular group consisting of the Intra modes from mode 8 through mode 12 and a second modified angular group comprising more modes than the first modified angular group, wherein the angle formed by the first modified angular group is substantially the same as the angle formed by the first angular group, and the second MDCS uses the vertical coefficient scanning for the first modified angular group and the non-vertical coefficient scanning for the second modified angular group;
receive input data associated with a current block;
determine whether the current block corresponds to a 2N×2N block or an N×2N block, wherein N is a positive integer;
when the current block corresponds to the 2N×2N block, process the current block according to the first MDCS, wherein the vertical coefficient scanning is applied to the current block if a current intra mode of the current block belongs to the first angular group, and the non-vertical coefficient scanning is applied to the current block if the current intra mode of the current block belongs to the second angular group; and
when the current block corresponds to the N×2N block, process the current block according to the second MDCS, wherein the vertical coefficient scanning is applied to the current block if the current intra mode of the current block belongs to the first modified angular group, and the non-vertical coefficient scanning is applied to the current block if the current intra mode of the current block belongs to the second modified angular group wherein the second angular group consists of the Intra modes having mode 22 through mode 30; and the Intra modes in the second modified angular group is between mode 18 through mode 34.
7. The apparatus of claim 6 , wherein the non-vertical coefficient scanning corresponds to a horizontal coefficient scanning or a diagonal coefficient scanning.
8. The apparatus of claim 6 , wherein when the current block corresponds to the 2N×2N block, the current block is associated with a 2N×2N luma block in a picture using 4:2:2 color sub-sampling.
9. The apparatus of claim 6 , wherein when the current block corresponds to the N×2N block, the current block is associated with a N×2N chroma block in a picture using 4:2:2 color sub-sampling.
10. The apparatus of claim 6 , wherein N is 2 or 4.
11. A non-transitory computer readable medium storing a computer-executable program, the computer-executable program, when executed, causing a decoder to perform the following steps:
specifying a first mode-dependent coefficient scanning (MDCS) for a plurality of Intra modes, wherein the plurality of Intra modes have mode 2 through mode 18 covers from −135 degree direction to −45 degree direction and mode 18 through mode 34 covers from −45 degree direction to +45 degree direction, wherein mode 10 corresponds to −90 degree direction and mode 26 corresponds to 0 degree direction, wherein the plurality of Intra modes are divided into multiple groups comprising a first angular group consisting of the Intra modes from mode 6 through mode 14 and a second angular group, and the first MDCS uses a vertical coefficient scanning for the first angular group and a non-vertical coefficient scanning for the second angular group;
specifying a second MDCS for a plurality of Intra modes, wherein the plurality of Intra modes are divided into multiple groups comprising a first modified angular group consisting of the Intra modes from mode 8 through mode 12 and a second modified angular group comprising more modes than the first modified angular group, wherein the angle formed by the first modified angular group is substantially the same as the angle formed by the first angular group, and the second MDCS uses the vertical coefficient scanning for the first modified angular group and the non-vertical coefficient scanning for the second modified angular group;
receiving input data associated with a current block;
determining whether the current block corresponds to a 2N×2N block or an N×2N block, wherein N is a positive integer;
when the current block corresponds to the 2N×2N block, processing the current block according to the first MDCS, wherein the vertical coefficient scanning is applied to the current block if a current intra mode of the current block belongs to the first angular group, and the non-vertical coefficient scanning is applied to the current block if the current intra mode of the current block belongs to the second angular group; and
when the current block corresponds to the N×2N block, processing the current block according to the second MDCS, wherein the vertical coefficient scanning is applied to the current block if the current intra mode of the current block belongs to the first modified angular group, and the non-vertical coefficient scanning is applied to the current block if the current intra mode of the current block belongs to the second modified angular group wherein the second angular group consists of the Intra modes having mode 22 through mode 30; and the Intra modes in the second modified angular group is between mode 18 through mode 34.