Method and device for intra prediction
A method for decoding an image according to the present invention comprises the steps of: receiving and decoding MPM index information for indicating an MPM candidate which is to be used as an intra prediction mode of a current block; generating an MPM candidate list containing a plurality of MPM candidates for the current block; determining the MPM candidate indicated by the decoded MPM index information as the intra prediction mode of the current block, among the plurality of the MPM candidates which constitute the MPM candidate list; and generating a prediction block corresponding to the current block by performing intra prediction for the current block based on the determined intra prediction mode.
1. A video decoding method, comprising:
receiving, by a decoding apparatus, index information indicating a candidate mode used as an intra prediction mode of a current block;
receiving, by the decoding apparatus, information related to a residual sample for the current block;
constructing, by the decoding apparatus, a candidate mode list including a plurality of candidate modes for the current block;
determining, by the decoding apparatus, a candidate mode indicated by the index information from among the plurality of candidate modes constituting the candidate mode list as the intra prediction mode of the current block;
deriving, by the decoding apparatus, a predicted sample by performing an intra prediction for the current block based on the determined intra prediction mode;
deriving, by the decoding apparatus, the residual sample of the current block based on the information related to the residual sample;
deriving, by the decoding apparatus, a reconstructed sample of the current block based on the predicted sample and the residual sample; and
applying, by the decoding apparatus, a deblocking filter to the reconstructed sample,
wherein the constructing the candidate mode list includes:
determining a first intra mode corresponding to a first block adjacent to a left side of the current block and a second intra mode corresponding to a second block adjacent to an upper side of the current block; and
setting a firstly ordered candidate mode and a secondly ordered candidate mode, among the candidate modes of the candidate mode list, based on the first block and the second block,
wherein the firstly ordered candidate mode is set equal to a planar mode and the secondly ordered candidate mode is set equal to a DC mode based on the first intra mode being the planar mode and the second block being unavailable,
wherein the firstly ordered candidate mode is set equal to the planar mode and the secondly ordered candidate mode is set equal to the DC mode based on both the first block and the second block being unavailable, and
wherein the firstly ordered candidate mode is set equal to the first intra mode and the secondly ordered candidate mode is set equal to the second intra mode based on the first intra mode being different from the second intra mode.
2. The method of claim 1 ,
wherein the constructing the candidate mode list includes
setting the first intra mode to be a DC mode based on the first block being not available, and setting the second intra mode to be a DC mode based on the second block being not available.
3. The method of claim 2 ,
wherein the constructing the candidate mode list includes
determining that the first block is not available based on the first block being located outside a current picture, a current slice or a current coding tree block, and determining that the second block is not available based on the second block being located outside of the current picture, the current slice or a current coding tree block.
4. The method of claim 2 ,
wherein the constructing the candidate mode list includes
determining that the first block is not available based on the first block being not a block decoded with an intra mode and determining that the second block is not available based on the second block being not a block decoded with an intra mode.
5. The method of claim 1 ,
wherein an index value of 0 is allocated to the firstly ordered candidate mode set to a first position in the candidate mode list and an index value of 1 is allocated to the secondly ordered candidate mode set to a second position in the candidate mode list.
6. The method of claim 1 ,
wherein the constructing the candidate mode list includes:
setting the planar mode to a thirdly ordered candidate mode in the candidate mode list based on neither of the first intra mode and the second intra mode being the planar mode,
setting the DC mode to the thirdly ordered candidate mode in the candidate mode list based on one of the first intra mode and the second intra mode being the planar mode and neither of the first intra mode and the second intra mode being the DC mode, and
setting a vertical mode to the thirdly ordered candidate mode in the candidate mode list based on one of the first intra mode and the second intra mode being the planar mode and the other being the DC mode.
7. The method of claim 6 ,
wherein an index value of 2 is allocated to the thirdly ordered candidate mode set to a third position in the candidate mode list.
8. The method of claim 1 ,
wherein the constructing the candidate mode list includes
setting the planar mode to the firstly ordered candidate mode in the candidate mode list and setting the DC mode to the secondly ordered candidate mode in the candidate mode list based on the first intra mode and the second intra mode being the planar mode.
9. The method of claim 1 ,
wherein the constructing the candidate mode list includes
setting the planar mode to the firstly ordered candidate mode in the candidate mode list and setting the DC mode to the secondly ordered candidate mode in the candidate mode list based on the first intra mode and the second intra mode being the DC mode.
10. The method of claim 1 ,
wherein the constructing the candidate mode list includes
setting the first intra mode to the firstly ordered candidate mode in the candidate mode list and setting a prediction mode having a prediction direction most similar or adjacent to a prediction direction of the first intra mode to the secondly ordered candidate mode in the candidate mode list based on the first intra mode being neither the planar mode nor the DC mode.
11. The method of claim 1 ,
further comprising receiving and decoding a flag specifying whether a candidate mode to be used as the intra prediction mode of the current block is present in the candidate modes constituting the candidate mode list.
12. A video encoding method, comprising:
constructing, by an encoding apparatus, a candidate mode list including a plurality of candidate modes for a current block;
determining, by the encoding apparatus, an intra prediction mode of the current block from among the plurality of candidate modes constituting the candidate mode list;
deriving, by the encoding apparatus, a prediction sample by performing an intra prediction for the current block based on the intra prediction mode;
generating, by the encoding apparatus, index information indicating the intra prediction mode of the current block;
deriving, by the encoding apparatus, a residual sample based on the prediction sample;
generating, by the encoding apparatus, information related to the residual sample; and
generating, by the encoding apparatus, a bitstream including the index information and the information related to the residual sample,
wherein the constructing the candidate mode list includes:
determining a first intra mode corresponding to a first block adjacent to a left side of the current block and a second intra mode corresponding to a second block adjacent to an upper side of the current block; and
setting a firstly ordered candidate mode and a secondly ordered candidate mode, among the candidate modes of the candidate mode list, based on the first block and the second block,
wherein the firstly ordered candidate mode is set equal to a planar mode and the secondly ordered candidate mode is set equal to a DC mode based on the first intra mode being the planar mode and the second block being unavailable,
wherein the firstly ordered candidate mode is set equal to the planar mode and the secondly ordered candidate mode is set equal to the DC mode based on both the first block and the second block being unavailable, and
wherein the firstly ordered candidate mode is set equal to the first intra mode and the secondly ordered candidate mode is set equal to the second intra mode based on the first intra mode being different from the second intra mode.
13. The method of claim 12 ,
wherein the constructing the candidate mode list includes
setting the first intra mode to be a DC mode based on the first block being not available, and setting the second intra mode to be a DC mode based on the second block being not available.
14. The method of claim 12 ,
wherein the constructing the candidate mode list includes:
setting the planar mode to a thirdly ordered candidate mode in the candidate mode list based on neither of the first intra mode and the second intra mode being the planar mode,
setting the DC mode to the thirdly ordered candidate mode in the candidate mode list based on one of the first intra mode and the second intra mode being the planar mode and neither of the first intra mode and the second intra mode being the DC mode, and
setting a vertical mode to the thirdly ordered candidate mode in the candidate mode list based on one of the first intra mode and the second intra mode being the planar mode and the other being the DC mode.
15. A non-transitory computer-readable storage medium storing an encoded video information generated by a video encoding method, the method comprising:
constructing, by an encoding apparatus, a candidate mode list including a plurality of candidate modes for a current block;
determining, by the encoding apparatus, an intra prediction mode of the current block from among the plurality of candidate modes constituting the candidate mode list;
deriving, by the encoding apparatus, a prediction sample by performing an intra prediction for the current block based on the intra prediction mode;
generating index information indicating the intra prediction mode of the current block;
deriving, by the encoding apparatus, a residual sample based on the prediction sample;
generating information related to the residual sample; and
generating, by the encoding apparatus, a bitstream including the index information and the information related to the residual sample,
wherein the constructing the candidate mode list includes:
determining a first intra mode corresponding to a first block adjacent to a left side of the current block and a second intra mode corresponding to a second block adjacent to an upper side of the current block; and
setting a firstly ordered candidate mode and a secondly ordered candidate mode, among the candidate modes of the candidate mode list, based on the first block and the second block,
wherein the firstly ordered candidate mode is set equal to a planar mode and the secondly ordered candidate mode is set equal to a DC mode based on the first intra mode being the planar mode and the second block being unavailable,
wherein the firstly ordered candidate mode is set equal to the planar mode and the secondly ordered candidate mode is set equal to the DC mode based on both the first block and the second block being unavailable, and
wherein the firstly ordered candidate mode is set equal to the first intra mode and the secondly ordered candidate mode is set equal to the second intra mode based on the first intra mode being different from the second intra mode.