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: deriving an intra-prediction mode of a current block; deriving upper neighboring samples and left neighboring samples of the current block; and generating a prediction sample of the current block based on the upper neighboring samples and the left neighboring samples and the intra-prediction mode, wherein the upper neighboring samples include upper neighboring samples of a n-th row, wherein the left neighboring samples include left neighboring samples of a n-th column, and wherein, when an upper neighboring sample, which is a fractional sample is included in specific upper neighboring samples derived based on a prediction direction of the current block, a sample value of the upper neighboring sample, which is the fractional sample is derived through linear interpolation between sample values of integer samples adjacent to the left and right of the upper neighboring sample, which is the fractional sample.
2. The method of claim 1 , wherein the n is more than 1,
wherein the number of the upper neighboring samples of the n-th row is more than 2N.
3. The method of claim 2 , wherein upper neighboring samples after an 2N-th upper neighboring sample among the upper neighboring samples of the n-th row are derived by padding a specific upper neighboring sample,
wherein the specific upper neighboring sample is a upper neighboring sample closest to the upper neighboring samples after the 2N-th upper neighboring sample among the upper neighboring samples of the n-th row other than the upper neighboring samples after an 2N-th upper neighboring sample.
4. The method of claim 3 , wherein the specific upper neighboring sample is the 2N-th upper neighboring sample among the upper neighboring samples of the n-th row.
5. The method of claim 1 , wherein the n is more than 1,
wherein the number of the left neighboring samples of the n-th column is more than 2N.
6. The method of claim 5 , wherein left neighboring samples after an 2N-th left neighboring sample among the left neighboring samples of the n-th column are derived by padding a specific left neighboring sample,
wherein the specific left neighboring sample is a left neighboring sample closest to the left neighboring samples after the 2N-th left neighboring sample among the left neighboring samples of the n-th column other than the left neighboring samples after an 2N-th left neighboring sample.
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. The method of claim 8 , wherein the number of the (n+1)th row of upper neighboring samples is more than 2N, and
upper neighboring samples after an 2N-th upper neighboring sample among the (n+1)th row of upper neighboring samples are derived by padding the 2N-th upper neighboring sample among the (n+1)th row of upper neighboring samples.
10. The method of claim 8 , wherein, before a prediction sample of the current block is generated, when reconstructed samples corresponding to upper neighboring samples after the 2N-th upper neighboring sample among the (n+1)th row of upper neighboring samples are generated, the reconstructed samples are derived as upper neighboring samples after the 2N-th row upper neighboring sample.
11. A method of encoding video performed by an encoding device, the method comprising: determining an intra-prediction mode of a current block; deriving upper neighboring samples and left neighboring samples of the current block; generating a prediction sample of the current block based on the upper reference samples and the left reference samples and the intra-prediction mode; and encoding prediction information of the current block, wherein the upper neighboring samples include upper neighboring samples of a n-th row, wherein the left neighboring samples include left neighboring samples of a n-th column, and wherein, when an upper neighboring sample, which is a fractional sample is included in specific upper neighboring samples derived based on a prediction direction of the current block, a sample value of the upper neighboring sample, which is the fractional sample is derived through linear interpolation between sample values of integer samples adjacent to the left and right of the upper neighboring sample, which is the fractional sample.
12. The method of claim 11 , wherein the n is more than 1,
wherein the number of the upper neighboring samples of the n-th row is more than 2N when a size of the current block is N×N.
13. The method of claim 11 , wherein the n is more than 1,
wherein the number of the left neighboring samples of the n-th column is more than 2N when a size of the current block is N×N.
14. A non-transitory computer-readable storage medium storing encoded video data comprising information on instructions, when executed, causing a video decoding device to perform operations comprising: deriving an intra-prediction mode of a current block; deriving upper neighboring samples and left neighboring samples of the current block; and generating a prediction sample of the current block based on the upper neighboring samples and the left neighboring samples and the intra-prediction mode, wherein the upper neighboring samples include upper neighboring samples of a n-th row, wherein the left neighboring samples include left neighboring samples of a n-th column, and wherein, when an upper neighboring sample, which is a fractional sample is included in specific upper neighboring samples derived based on a prediction direction of the current block, a sample value of the upper neighboring sample, which is the fractional sample is derived through linear interpolation between sample values of integer samples adjacent to the left and right of the upper neighboring sample, which is the fractional sample.