Method and Apparatus for Coding of Intra Prediction Mode

Abstract

A method for chroma intra prediction mode decoding includes decoding a chroma intra prediction mode for a current chroma block according to a codeword set corresponding to a chroma intra prediction mode set, wherein the codeword set comprises at least one codeword with a first length type and at least one codeword with a second length type. If a codeword is one of said at least one codeword with the first length type, the chroma intra prediction mode is decoded as a Luma-based chroma prediction Mode (LM) or a Direct Mode (DM). The method also includes determines the chroma intra prediction mode based on an intra prediction mode of a current luma block if the chroma intra prediction mode is the DM.

1 . A method for chroma intra prediction mode decoding, comprising:
 decoding a chroma intra prediction mode for a current chroma block according to a codeword set corresponding to a chroma intra prediction mode set, wherein the codeword set comprises at least one codeword with a first length type and at least one codeword with a second length type, wherein said at least one codeword with the second length type is longer than said at least one codeword with the first length type;   if a codeword is one of said at least one codeword with the first length type, the chroma intra prediction mode is decoded as a Luma-based chroma prediction Mode (LM) or a Direct Mode (DM);   determining the chroma intra prediction mode based on an intra prediction mode of a current luma block if the chroma intra prediction mode is the DM; and   if the codeword is one of said at least one codeword with the second length type, the chroma intra prediction mode is decoded as one of four modes other than the DM and the LM.   
     
     
         2 . The method of  claim 1 , wherein said four modes represented by said at least one codeword with the second length type are Planner mode, Vertical mode, Horizontal mode, and DC mode. 
     
     
         3 . The method of  claim 1 , further comprising:
 deriving the chroma intra prediction mode from reconstructed pixels of the current luma block if the chroma intra prediction mode is the LM.   
     
     
         4 . The method of  claim 1 , wherein said at least one codeword with the first length type corresponds to at least one variable-length codeword, and said at least one codeword with the second length type corresponds to at least one fixed-length codeword. 
     
     
         5 . The method of  claim 4 , wherein if the intra prediction mode of the current luma block is one of Planner mode, Vertical mode, Horizontal mode, and DC mode, one fixed-length codeword in the codeword set is assigned to an intra mode different from the Planner mode, Vertical mode, Horizontal mode, and DC mode. 
     
     
         6 . The method of  claim 4 , wherein the variable-length codewords are 1 bit or 2 bits, and the fixed-length codewords are 4 bits. 
     
     
         7 . The method of  claim 6 , wherein the codeword set consist of 1100, 1101, 1110, 1111, 10, and 0 corresponding to Planar mode, Vertical mode, Horizontal mode, DC mode, LM, and DM respectively 
     
     
         8 . The method of  claim 4 , wherein each codeword with the first length type is with 1 bit or 2 bits, and each codeword with the second length type is with N bits, wherein N is an integer greater than 2. 
     
     
         9 . A method for chroma intra prediction mode coding, comprising:
 determining a chroma intra prediction mode set comprising a Luma-based chroma prediction Mode (LM), a Direct Mode (DM), and four other modes, wherein the DM determines the chroma intra prediction mode based on an intra prediction mode of the current luma block; and   encoding the chroma intra prediction mode for a current chroma block using a codeword set corresponding to the chroma intra prediction mode set, wherein the codeword set comprises at least one codeword with a first length type for the DM, and at least one codeword with a second length type for said four other modes, and the said at least one codeword with the second length type is longer than said at least one codeword with the first length type.   
     
     
         10 . The method of  claim 9 , wherein said four other modes are Planner mode, Vertical mode, Horizontal mode, and DC mode. 
     
     
         11 . The method of  claim 9 , wherein said at least one codeword with the first length type corresponds to at least one variable-length codeword, and said at least one codeword with the second length type corresponds to at least one fixed-length codeword. 
     
     
         12 . The method of  claim 11 , wherein if the intra prediction mode of the current luma block is one of Planner mode, Vertical mode, Horizontal mode, and DC mode, one fixed-length codeword in the codeword set is assigned to an intra mode different from the Planner mode, Vertical mode, Horizontal mode, and DC mode. 
     
     
         13 . The method of  claim 11 , wherein the variable-length codewords are 1 bit or 2 bits, and the fixed-length codewords are 4 bits. 
     
     
         14 . The method of  claim 13 , wherein the codeword set consist of 1100, 1101, 1110, 1111, 10, and 0 corresponding to Planar mode, Vertical mode, Horizontal mode, DC mode, LM, and DM respectively. 
     
     
         15 . The method of  claim 9 , wherein each codeword with the first length type is with 1 bit or 2 bits, and each codeword with the second length type is with N bits, wherein N is an integer greater than 2. 
     
     
         16 . The method of  claim 9 , wherein the LM derives the chroma intra prediction mode from reconstructed pixels of a current luma block.