Intra prediction method of chrominance block using luminance sample, and apparatus using same
Disclosed are an intra prediction method of a chrominance block using a luminance sample and an apparatus using the same. An image decoding method comprises the steps of: calculating an intra prediction mode of a chrominance block on the basis of an LM mapping table when the chrominance block uses an LM; and generating a prediction block for the chrominance block on the basis of the calculated intra prediction mode of the chrominance block. When intra prediction mode information of chrominance blocks are decoded, mutually different tables are used depending on whether or not an LM is used, so that encoding and decoding can be performed without an unnecessary waste of bits.
1. An image encoding method performed by an encoding apparatus, the image encoding method comprising:
deriving an intra prediction mode of a luma block of a current block;
deriving an intra prediction mode of a chroma block of the current block;
performing a prediction for the chroma block of the current block based on the intra prediction mode of the chroma block of the current block;
generating intra_chroma_pred_mode information for deriving the intra prediction mode of the chroma block based on the intra prediction mode of the luma block and the intra prediction mode of the chroma block; and
encoding image information including information on the prediction for the chroma block of the current block or the intra_chroma_pred_mode information,
wherein the current block is split from a largest coding unit based on a quad tree structure,
wherein the intra_chroma_pred_mode information represents one value among 0 to 4, and the intra prediction mode of the chroma block is equal to the intra prediction mode of the luma block when a value of the intra_chroma_pred_mode information is 4,
wherein a binarization value corresponding to a case when the intra_chroma_pred_mode information value is 4 is ‘0’, and binarization values corresponding to cases when a value of the intra_chroma_pred_mode information is 0 to 3 are ‘100’, ‘101’, ‘110’, and ‘111’ respectively, and
wherein a first bit of a binarization value for deriving the one value among the 0 to 4 of the intra_chroma_pred_mode information is encoded based on context coding, and the remaining bits are encoded based on bypass coding.
2. The method of claim 1 , wherein the intra prediction mode of the chroma block is determined based on a pre-determined table, and the pre-determined table represents the intra prediction mode of the chroma block depend on the intra chroma prediction mode indices and the intra prediction mode of the luma block.
3. The method of claim 1 , wherein the intra_chroma_pred_mode information represents one of intra chroma prediction mode indices, and the intra prediction mode of the chroma block is determined based on the represented one of the intra chroma prediction mode indices and the intra prediction mode of the luma block.
4. The method of claim 3 , wherein the intra_chroma_pred_mode information represents a bin string related to the one of the intra chroma prediction mode indices including a first index to a fifth index, and
wherein the first index represents an upper-right diagonal mode for the intra prediction mode of the chroma block based on the intra prediction mode of the luma block which is a planar mode, and the first index represents the planar mode for the intra prediction mode of the chroma block based on the intra prediction mode of the luma block which is not the planar mode.
5. The method of claim 4 , wherein the upper-right diagonal mode represents a 34th intra prediction mode.
6. A decoding apparatus readable digital storage medium storing information on instructions, wherein the information on the instructions causes the decoding apparatus to perform an image decoding method, the image decoding method comprising receiving image information including intra_chroma_pred_mode information for deriving an intra prediction mode of a chroma block of a current block, deriving the intra prediction mode of the chroma block based on the intra_chroma_pred_mode information and an intra prediction mode of a luma block of the current block, deriving a predicted block by performing an intra prediction for the chroma block based on the intra prediction mode of the chroma block, and generating a reconstructed picture based on the predicted block,
wherein the current block is split from a largest coding unit based on a quad tree structure,
wherein the intra_chroma_pred_mode information represents one value among 0 to 4, and the intra prediction mode of the chroma block is equal to the intra prediction mode of the luma block when a value of the intra_chroma_pred_mode information is 4,
wherein a binarization value corresponding to a case when the intra_chroma_pred_mode information value is 4 is ‘0’, and binarization values corresponding to cases when a value of the intra_chroma_pred_mode information is 0 to 3 are ‘100’, ‘101’, ‘110’, and ‘111’ respectively, and
wherein a first bit of a binarization value for deriving the one value among the 0 to 4 of the intra_chroma_pred_mode information is encoded based on context coding, and the remaining bits are encoded based on bypass coding.