Method and apparatus for video signal processing determining reference sample lines for a prediction target sample

1. A method of decoding an image, the method comprising:

deriving reference samples of a current block, the reference samples comprising top reference samples and left reference samples;

determining an intra prediction mode of the current block; and

obtaining a prediction block of the current block based on the intra prediction mode and the reference samples,

wherein the method further comprises determining whether to apply an update process of the prediction block to the current block or not,

wherein, when it is determined to apply the update process, whether to update a prediction sample, derived by a first reference sample, in the current block by using a second reference sample or not is determined by comparing a coordinate value of the prediction sample with a first threshold value, and

wherein the first reference sample is one of the top reference samples and the second reference sample is one of the left reference samples.

2. The method of claim 1 , wherein an updated prediction sample is obtained based on a weighted sum operation of the prediction sample and the second reference sample.

3. The method of claim 2 , wherein weights applied to the prediction sample and the second reference sample are determined based on a position of the prediction sample.

4. The method of claim 1 , wherein the method further comprises:

determining a reference sample line of the current block based on index information specifying one of a plurality of reference sample line candidates, the plurality of reference sample line candidates comprising a neighboring reference sample line and non-neighboring reference sample lines,

wherein when the index information is explicitly signaled via a bitstream, a reference sample line candidate who has an index identical to the index information is determined as the reference sample line of the current block, and

wherein when the index information is not explicitly signaled via the bitstream, the neighboring reference sample line is determined as the reference sample line of the current block.

5. A method of encoding an image, the method comprising:

deriving reference samples of a current block, the reference samples comprising top reference samples and left reference samples;

determining an intra prediction mode of the current block; and

obtaining a prediction block of the current block based on the intra prediction mode and the reference samples,

wherein the method further comprises determining whether to apply an update process of the prediction block to the current block or not,

wherein, when it is determined to apply the update process, whether to update a prediction sample, derived by a first reference sample, in the current block by using a second reference sample or not is determined by comparing a coordinate value of the prediction sample with a threshold value, and

wherein the first reference sample is one of the top reference samples and the second reference sample is one of the left reference samples.

6. The method of claim 5 , wherein an updated prediction sample is obtained based on a weighted sum operation of the prediction sample and the second reference sample.

7. The method of claim 6 , wherein weights applied to the prediction sample and the second reference sample are determined based on a position of the prediction sample.

8. The method of claim 4 , wherein in response that the current block adjoins a boundary of a coding tree unit, only the neighboring reference sample line is available as the reference sample line of the current block.

9. The method of claim 4 , wherein in response that the current block is partitioned into a plurality of sub-blocks, only the neighboring reference sample line is available as the reference sample line of the current block.

10. The method of claim 4 , wherein determining the intra prediction mode of the current block comprises:

determining whether there exists a Most Probable Mode (MPM) candidate identical to the intra prediction mode of the current block,

wherein when it is determined that there exists the MPM candidate identical to the intra prediction mode of the current block, the intra prediction mode of the current block is determined to be the same as one of MPM candidates, and

wherein when it is determined that there does not exist the MPM candidate identical to the intra prediction mode of the current block, the intra prediction mode of the current block is determined to be one of remaining intra prediction modes other than the MPM candidates.

11. The method of claim 10 , wherein whether there exists the MPM candidate identical to the intra prediction mode or not is determined based on an MPM flag, and

wherein when an index of the reference sample line is greater than a second threshold value, the MPM flag is not explicitly signaled via the bitstream, and it is inferred that the MPM flag indicates there exists the MPM candidate identical to the intra prediction mode.

12. A non-transitory computer readable medium having stored thereon a compressed video data, the compressed video data comprising:

a reference sample line index specifying a reference sample line of a current block,

wherein reference samples included in the reference sample line are derived from reconstructed samples, the reference samples comprising top reference samples and left reference samples,

wherein a prediction block of the current block is obtained based on an intra prediction mode of the current block and the reference samples,

wherein, when it is determined to apply an update process of the prediction block to the current block, whether to update a prediction sample, derived by a first reference sample, in the current block by using a second reference sample or not is determined by comparing a coordinate value of the prediction sample with a threshold value, and

wherein the first reference sample is one of the top reference samples and the second reference sample is one of the left reference samples.