Extended directional predictions for residual blocks
The various implementations described herein include methods and systems for coding video. In one aspect, a method of video decoding includes receiving video data comprising a plurality of blocks, including a first block and a plurality of residual coefficients, from a video bitstream. The first block is encoded by applying a first intra prediction. The plurality of residual coefficients are generated by applying a second intra prediction to a residue block for the first block in a first direction. The residue block generated from applying the first intra prediction mode to the first block in a second direction. The method also includes generating, from the plurality of residual coefficients, a refined residue block for the first block, and reconstructing the first block using the refined residue block.
1 . A method of video decoding performed at a computing system having memory and one or more processors, the method comprising:
receiving video data comprising a plurality of blocks, including a first block and a plurality of residual coefficients for the first block, from a video bitstream;
generating, from the plurality of residual coefficients, a refined residue block for the first block;
generating a reconstructed residue block from the refined residue block by applying a first intra prediction in a first direction to the refined residue block, wherein the first intra prediction is a line-by-line prediction in which residues in a particular line of the refined residue block are predicted using an adjacent preceding line of the refined residue block or a bi-directional prediction in which residues in the particular line of the refined residue block are predicted using a weighted average of residues in preceding lines of the refined residue block; and
reconstructing the first block from the reconstructed residue block by applying a second intra prediction, different from the first intra prediction, in a second direction to the reconstructed residue block.
2 . The method of claim 1 , wherein the plurality of residual coefficients corresponds to differences between (i) residues of a residue block for the first block and (ii) predicted residues obtained from applying the first intra prediction to the residue block.
3 . The method of claim 1 , wherein the second direction is used as context for entropy coding the first direction.
4 . The method of claim 1 , wherein the first intra prediction is a short distance intra prediction.
5 . The method of claim 4 , wherein the short distance intra prediction comprises the line-by-line prediction in which residues in a particular row or column are predicted using an adjacent preceding row or column.
6 . The method of claim 4 , wherein the short distance intra prediction comprises the bi-directional prediction in which residues in a third index line and a fourth index line are predicted using a weighted average of residues in a first index line and a second index line.
7 . The method of claim 1 , wherein the first direction is selected from a group consisting of N nominal angles used for intra predictions, N being a positive integer.
8 . The method of claim 1 , wherein the video bitstream includes one or more syntax elements that indicate a direction and/or angle of the first intra prediction.
9 . The method of claim 8 , wherein the one or more syntax elements include a first syntax indicating a nominal direction and a second syntax indicating an angle delta applied to the nominal direction.
10 . The method of claim 8 , wherein the one or more syntax elements include a first syntax element indicating a nominal direction, a second syntax element indicating whether an angle delta is zero, a third syntax element indicating whether the angle delta is positive or negative, and a fourth syntax element indicating an absolute angle delta.
11 . A method of video encoding performed at a computing system having memory and one or more processors, the method comprising:
receiving video data comprising a plurality of blocks, including a first block, wherein the first block is to be encoded in a first intra prediction mode;
generating a residue block for the first block by applying the first intra prediction mode to the first block in a first direction;
generating a refined residue block from the residue block by applying a second intra prediction, different from the first intra prediction, to the residue block in a second direction, wherein the second intra prediction is a line-by-line prediction in which residues in a particular line of the residue block are predicted using an adjacent preceding line of the residue block or a bi-directional prediction in which residues in the particular line of the residue block are predicted using a weighted average of residues in preceding lines of the residue block; and
signaling the refined residue block via a video bitstream.
12 . The method of claim 11 , wherein the first direction is used as context for entropy coding the second direction.
13 . The method of claim 11 , wherein the second direction is selected from a group consisting of N nominal angles used for intra predictions, N being a positive integer.
14 . The method of claim 11 , wherein the second intra prediction is a short distance intra prediction.
15 . The method of claim 14 , wherein the short distance intra prediction comprises the line-by-line prediction in which residues in a particular row or column are predicted using an adjacent preceding row or column.
16 . The method of claim 14 , wherein the short distance intra prediction comprises the bi-directional prediction in which residues in a third index line and a fourth index line are predicted using a weighted average of residues in a first index line and a second index line.
17 . The method of claim 11 , further comprising signaling, via one or more syntax elements, a direction and/or angle of the second intra prediction.
18 . A non-transitory computer-readable storage medium storing a video bitstream that is generated by a video encoding method, the video bitstream comprising:
coded information corresponding to a plurality of blocks of video data, the plurality of blocks including a first block encoded in a first intra prediction mode, and the coded information including a plurality of residual coefficients for the first block; and
the video encoding method comprising:
generating a residue block for the first block by applying the first intra prediction mode to the first block in a first direction;
generating a refined residue block from the residue block by applying a second intra prediction, different from the first intra prediction, to the residue block in a second direction, wherein the second intra prediction is a line-by-line prediction in which residues in a particular line of the residue block are predicted using an adjacent preceding line of the residue block or a bi-directional prediction in which residues in the particular line of the residue block are predicted using a weighted average of residues in preceding lines of the residue block.
19 . The non-transitory computer-readable storage medium of claim 18 , wherein the video bitstream includes one or more syntax elements that indicate a direction and/or angle of the first intra prediction.
20 . The non-transitory computer-readable storage medium of claim 18 , wherein the second direction is used as context for entropy coding the first direction.