Video signal processing method and device for performing intra-prediction for an encoding/decoding target block
A method for decoding a video according to the present invention may comprise: deriving a plurality of reference sample lines for a current block, selecting at least two among the plurality of reference sample lines, and performing intra prediction for the current block based on the selected reference sample lines.
1. A method for decoding a video, the method comprising:
determining a position of a reference sample line based on index information decoded from a bitstream, the index information indicating the reference sample line among a plurality of reference sample lines;
deriving reference samples included in the reference sample line, the reference samples being derived from reconstruction samples prior to applying an in-loop filter;
determining whether to apply a smoothing filter to the reference samples included in the reference sample line;
determining an intra prediction mode; and
performing intra prediction for the current block based on filtered or unfiltered reference samples and the intra prediction mode,
wherein whether to apply the smoothing filter to the reference samples or not is implicitly determined based on the position of the reference sample line,
wherein it is determined to apply the smoothing filter to the reference samples in response to a case where the position of the reference sample line corresponds to a first reference sample line of the plurality of reference sample lines while it is determined not to apply the smoothing filter to the reference samples in response to a case where the position of the reference sample line corresponds to a second reference sample line of the plurality of reference sample lines,
wherein when it is determined to apply the smoothing filter, a reference sample included in the reference sample line is filtered by using neighboring reference samples included in the same reference sample line,
wherein the intra prediction is performed by selectively using one of the plurality of reference sample lines in response to the current block being a square coding block while the intra prediction is performed by using only a reference sample line adjacent to the current block in response to the current block being one of non-square partitions generated by partitioning the square coding block in a horizontal direction or a vertical direction, and
wherein a number of the intra prediction modes available for the current block is different between when an index of the reference sample line is greater than a threshold value and when the index of the reference sample line is equal to or less than the threshold value.
2. The method of claim 1 , wherein if an unavailable reference sample is included in the reference sample line, the unavailable reference sample is replaced with an available reference sample included in the reference sample line.
3. The method of claim 1 , wherein when the intra prediction mode of the current block has a direction of top-right diagonal or bottom-left diagonal, a prediction sample resultant from the intra prediction is modified by using a reference sample included in a neighboring block adjacent to the current block.
4. The method of claim 3 , wherein the reference sample comprises at least one of a sample toward a reverse direction of the intra prediction mode.
5. A method for encoding a video, the method comprising:
determining a position of a reference sample line;
determining an intra prediction mode;
determining whether to apply a smoothing filter to reference samples included in the reference sample line;
performing intra prediction for a current block based on filtered or unfiltered reference samples included in the reference sample line and the intra prediction mode; and
encoding index information specifying the reference sample line among a plurality of reference sample lines,
wherein whether to apply the smoothing filter to the reference samples or not is implicitly determined based on the position of the reference sample line,
wherein it is determined to apply the smoothing filter to the reference samples in response to a case where the position of the reference sample line corresponds to a first reference sample line of the plurality of reference sample lines while it is determined not to apply the smoothing filter to the reference samples in response to a case where the position of the reference sample line corresponds to a second reference sample line of the plurality of reference sample lines,
wherein when it is determined to apply the smoothing filter, a reference sample included in the reference sample line is filtered by using neighboring reference samples included in the same reference sample line,
wherein the intra prediction is performed by selectively using one of the plurality of reference sample lines in response to the current block being a square coding block while the intra prediction is performed by using only a reference sample line adjacent to the current block in response to the current block being one of non-square partitions generated by partitioning the square coding block in a horizontal direction or a vertical direction, and
wherein a number the intra prediction modes available for the current block is different between when an index of the reference sample line is greater than a threshold value and when the index of the reference sample line is equal to or less than the threshold value.
6. The method of claim 5 , wherein if an unavailable reference sample is included in the reference sample line, the unavailable reference sample is replaced with an available reference sample included in the reference sample line.
7. The method of claim 5 , wherein when the intra prediction mode of the current block has a direction of top-right diagonal or bottom-left diagonal, a prediction sample resultant from the intra prediction is modified by using a reference sample included in a neighboring block adjacent to the current block.
8. The method of claim 7 , wherein the reference sample comprises at least one of a sample toward a reverse direction of the intra prediction mode.
9. A non-transitory computer-readable medium for storing compressed data associated with a video signal, the compressed data comprising:
index information specifying one of a plurality of reference sample lines,
wherein a position of a reference samples line is determined based on the index information,
wherein reference samples included in the reference sample line are derived from reconstruction samples prior to applying an in-loop filter,
wherein intra prediction for the current block is performed based on filtered or unfiltered reference samples and an intra prediction mode of the current block,
wherein whether to apply a smoothing filter to the reference samples or not is implicitly determined based on the position of the reference sample line,
wherein it is determined to apply the smoothing filter to the reference samples in response to a case where the position of the reference sample line corresponds to a first reference sample line of the plurality of reference sample lines while it is determined not to apply the smoothing filter to the reference samples in response to a case where the position of the reference sample line corresponds to a second reference sample line of the plurality of reference sample lines,
wherein when it is determined to apply the smoothing filter, a reference sample included in the reference sample line is filtered by using neighboring reference samples included in the same reference sample line,
wherein the intra prediction is performed by selectively using one of the plurality of reference sample lines in response to the current block being a square coding block while the intra prediction is performed by using only a reference sample line adjacent to the current block in response to the current block being one of non-square partitions generated by partitioning the square coding block in a horizontal direction or a vertical direction, and
wherein a number of the intra prediction modes available for the current block is different between when an index of the reference sample line is greater than a threshold value and when the index of the reference sample line is equal to or less than the threshold value.
10. The method of claim 1 , wherein when the current block is one of partitions generated by partitioning a coding block, the index information is shared to all of the partitions included in the coding block.
11. The method of claim 1 , wherein when the intra prediction mode is DC mode, prediction samples of the current block are derived based on an average value derived by a first derivation method or a second derivation method,
wherein the first derivation method represents that the average value is derived by using both top reference samples and left reference samples,
wherein the second derivation method represents that the average value is derived by a part of the top reference samples and the left reference samples, and
wherein a selection of one of the first derivation method and the second derivation method is based on a shape of the current block.
12. The method of claim 1 , wherein the method further comprises:
reconstructing the current block based on prediction samples, resultant from the intra prediction, and residual samples,
wherein the residual samples are obtained by skipping or performing an inverse-transform for the current block, and
wherein when the current block is one of the partitions generated by partitioning the coding block in a horizontal direction or in a vertical direction, a transform skip flag indicating whether the inverse-transform is skipped or not is not parsed from the bitstream, and it is not allowed to skip the inverse-transform for the current block.