Image decoding method and apparatus relying on intra prediction in image coding system
An image decoding method performed by a decoding apparatus according to the present invention comprises: a step of deriving an intra prediction mode for a current block; a step of deriving upper neighboring samples of a plurality of rows for the current block, and left neighboring samples of a plurality of columns; a step of deriving one row of upper reference samples on the basis of the upper neighboring samples; a step of deriving one column of left reference samples on the basis of the left neighboring samples; and a step of generating a prediction sample for the current block by using at least one of the upper reference samples and the left reference samples in accordance with the intra prediction mode.
1. A method of decoding video performed by a decoding device, the method comprising:
obtaining information related to an intra prediction mode and residual signal through a bitstream;
deriving residual samples of a current block based on the residual signal;
deriving an intra prediction mode of the current block based on the information related to the intra prediction mode;
deriving upper neighboring samples and left neighboring samples of the current block;
deriving prediction samples of the current block based on the upper neighboring samples, the left neighboring samples and the intra prediction mode of the current block; and
generating reconstructed samples of the current block based on the prediction samples and the residual samples,
wherein the upper neighboring samples include upper neighboring samples of a n-th row located in an upward direction away from an uppermost row of the current block,
wherein the left neighboring samples include left neighboring samples of a n-th column located in a left direction away from a leftmost column of the current block,
wherein n is positive integer more than 1, a number of the upper neighboring samples of the n-th row is more than 2N based on a size of the current block is N×N, and N is a positive integer,
wherein additional upper neighboring samples after a 2N-th upper neighboring sample among the upper neighboring samples of the n-th row are derived by padding a specific upper neighboring sample without checking whether the additional upper neighboring samples among the upper neighboring samples of the n-th row are available, and
wherein the specific upper neighboring sample is a upper neighboring sample closest to the additional upper neighboring samples other than the additional upper neighboring samples among the upper neighboring samples of the n-th row.
2. The method of claim 1 , wherein an 1-th upper neighboring sample among the upper neighboring samples of the n-th row is located along a vertical direction with regard to a top-leftmost sample position of the current block and an N-th upper neighboring sample among the upper neighboring samples of the n-th row is located along a vertical direction with regard to a top-rightmost sample position of the current block.
3. The method of claim 1 , wherein the specific upper neighboring sample is the 2N-th upper neighboring sample among the upper neighboring samples of the n-th row.
4. The method of claim 1 , wherein based on an upper reference sample which is derived based on a prediction direction of the current block and is positioned at a fractional sample position, a sample value of the upper reference sample positioned at the fractional sample position is derived through linear interpolation between sample values of upper neighboring samples positioned at integer sample positions which are adjacent to the left and right of the upper reference sample positioned at the fractional sample position.
5. The method of claim 1 ,
wherein a number of the left neighboring samples of the n-th column is more than 2N based on a size of the current block is N×N, and N is a positive integer.
6. The method of claim 5 , wherein additional left neighboring samples after a 2N-th left neighboring sample among the left neighboring samples of the n-th column are derived by padding a specific left neighboring sample without checking whether the additional left neighboring samples among the left neighboring samples of the n-th column are available, and
wherein the specific left neighboring sample is a left neighboring sample closest to the additional left neighboring samples other than the additional left neighboring samples among the left neighboring samples of the n-th column.
7. The method of claim 6 , wherein the left neighboring sample is the 2N-th left neighboring sample among the left neighboring samples of the n-th column.
8. The method of claim 1 , wherein the number of the upper neighboring samples of the n-th row is smaller than that of upper neighboring samples of an (n+1)th row, when a size of the current block is N×N.
9. A method of encoding video performed by an encoding device, the method comprising:
deriving an intra prediction mode of a current block;
deriving upper neighboring samples and left neighboring samples of the current block;
deriving prediction samples of the current block based on the upper neighboring samples, the left neighboring samples and the intra prediction mode of the current block;
deriving residual samples of the current block based on the prediction samples;
generating information related to an intra prediction mode and residual signal based on the intra prediction mode of the current block; and
encoding image information including the information related to the intra prediction mode and the residual signal to generate a bitstream,
wherein the upper neighboring samples include upper neighboring samples of a n-th row located in an upward direction away from an uppermost row of the current block,
wherein the left neighboring samples include left neighboring samples of a n-th column located in a left direction away from a leftmost column of the current block,
wherein n is positive integer more than 1, a number of the upper neighboring samples of the n-th row is more than 2N based on a size of the current block is N×N, and N is a positive integer,
wherein additional upper neighboring samples after a 2N-th upper neighboring sample among the upper neighboring samples of the n-th row are derived by padding a specific upper neighboring sample without checking whether the additional upper neighboring samples among the upper neighboring samples of the n-th row are available, and
wherein the specific upper neighboring sample is a upper neighboring sample closest to the additional upper neighboring samples other than the additional upper neighboring samples among the upper neighboring samples of the n-th row.
10. The method of claim 9 ,
wherein a number of the left neighboring samples of the n-th column is more than 2N based on a size of the current block is N×N, and N is a positive integer.
11. The method of claim 10 , wherein additional left neighboring samples after a 2N-th left neighboring sample among the left neighboring samples of the n-th column are derived by padding a specific left neighboring sample without checking whether the additional left neighboring samples among the left neighboring samples of the n-th column are available, and
wherein the specific left neighboring sample is a left neighboring sample closest to the additional left neighboring samples other than the additional left neighboring samples among the left neighboring samples of the n-th column.
12. A non-transitory computer-readable digital storage medium storing a bitstream generated by a video encoding method, the method comprising:
deriving an intra prediction mode of a current block;
deriving upper neighboring samples and left neighboring samples of the current block;
deriving prediction samples of the current block based on the upper neighboring samples, the left neighboring samples and the intra prediction mode of the current block;
deriving residual samples of the current block based on the prediction samples;
generating information related to an intra prediction mode and residual signal based on the intra prediction mode of the current block; and
encoding image information including the information related to the intra prediction mode and the residual signal to generate a bitstream,
wherein the upper neighboring samples include upper neighboring samples of a n-th row located in an upward direction away from an uppermost row of the current block,
wherein the left neighboring samples include left neighboring samples of a n-th column located in a left direction away from a leftmost column of the current block,
wherein n is positive integer more than 1, a number of the upper neighboring samples of the n-th row is more than 2N based on a size of the current block is N×N, and N is a positive integer,
wherein additional upper neighboring samples after a 2N-th upper neighboring sample among the upper neighboring samples of the n-th row are derived by padding a specific upper neighboring sample without checking whether the additional upper neighboring samples among the upper neighboring samples of the n-th row are available, and
wherein the specific upper neighboring sample is a upper neighboring sample closest to the additional upper neighboring samples other than the additional upper neighboring samples among the upper neighboring samples of the n-th row.