Angular intra prediction
Coded information of a current block and a plurality of reference lines of the current block is received. A first offset value is determined in a first mapping table and associated with a first reference line of the plurality of reference lines that is adjacent to the current block. A second offset value is determined in a second mapping table and associated with a second reference line of the plurality of reference lines that is adjacent to the first reference line. A first reference sample for a sample of the current block is determined from the first reference line based on the first offset value. A second reference sample for the sample of the current block is determined from the second reference line based on the second offset value. The sample of the current block is reconstructed based on one of the first reference sample and the second reference sample.
1. A method of video decoding performed in a video decoder, the method comprising:
receiving coded information of a current block and a plurality of reference lines of the current block from a coded video bitstream, each of the plurality of reference lines including a respective row of reference samples above a top side of the current block and a respective column of reference samples at a left side of the current block;
determining (i) a first offset value in an angle-to-offset mapping table and (ii) a second offset value in the angle-to-offset mapping table, the first offset value being associated with a first directional mode for a first reference line of the plurality of reference lines and a second directional mode for a second reference line of the plurality of reference lines, the first reference line being adjacent to the current block and the second reference line being adjacent to the first reference line, the second offset value being associated with the first directional mode for the first reference line of the plurality of reference lines and the second directional mode for the second reference line of the plurality of reference lines;
determining (i) a first reference sample for a sample of the current block from the first reference line based on the first offset value, and (ii) a second reference sample for the sample of the current block from the second reference line based on the second offset value; and
reconstructing the sample of the current block based on one of the first reference sample and the second reference sample.
2. The method of claim 1 , wherein:
the angle-to-offset mapping table indicates correlations between candidate directional modes and offset values that are associated with the current block and the first reference line, and
the angle-to-offset mapping table indicates correlations between candidate directional modes and offset values that are associated with the current block and the second reference line.
3. The method of claim 2 , wherein the first directional mode associated with the current block and the first reference line, and the second directional mode associated with the current block and the second reference line correspond to the first offset value.
4. The method of claim 3 , wherein a first difference between the first directional mode and the first offset value, a second difference between the second directional mode and the first offset value, and a third difference between the first directional mode and the second directional mode are within a predefined range.
5. The method of claim 4 , wherein the predefined range is equal to or larger than the first offset value minus a constant value, and equal to or smaller than the first offset value plus the constant value.
6. The method of claim 5 , wherein the constant value is one of 1, 2, 3, or 4.
7. The method of claim 1 , wherein the determining the first reference sample and the second reference sample further comprising:
determining the first reference sample from the reference samples of the first reference line based on a first directional angle, the first directional angle being equal to a sum of the first directional mode of the current block and the first offset value; and
determining the second reference sample from the reference samples of the second reference line based on a second directional angle, the second directional angle being equal to a sum of the second directional mode of the current block and the second offset value.
8. The method of claim 1 , wherein:
when the first directional mode and the second directional mode of the current block are larger than 45 degrees,
a difference of the first offset value and the second offset value is within a preset range.
9. The method of claim 1 , wherein an offset value for a chroma component of the current block is determined based on a reference line of the plurality of reference lines that is associated with a luma component of the current block.
10. An apparatus of video decoding, the apparatus comprising:
processing circuitry configured to:
receive coded information of a current block and a plurality of reference lines of the current block from a coded video bitstream, each of the plurality of reference lines including a respective row of reference samples above a top side of the current block and a respective column of reference samples at a left side of the current block;
determine (i) a first offset value in an angle-to-offset mapping table and (ii) a second offset value in the angle-to-offset mapping table, the first offset value being associated with a first directional mode for a first reference line of the plurality of reference lines and a second directional mode for a second reference line of the plurality of reference lines, the first reference line being adjacent to the current block and the second reference line is adjacent to the first reference line, and the second offset value being associated with the first directional mode for the first reference line of the plurality of reference lines and the second directional mode for the second reference line of the plurality of reference lines;
determine (i) a first reference sample for a sample of the current block from the first reference line based on the first offset value, and (ii) a second reference sample for the sample of the current block from the second reference line based on the second offset value; and
reconstruct the sample of the current block based on one of the first reference sample and the second reference sample.
11. The apparatus of claim 10 , wherein:
the angle-to-offset mapping table indicates correlations between candidate directional modes and offset values that are associated with the current block and the first reference line, and
the angle-to-offset mapping table indicates correlations between candidate directional modes and offset values that are associated with the current block and the second reference line.
12. The apparatus of claim 11 , wherein the first directional mode associated with the current block and the first reference line and the second directional mode associated with the current block and the second reference line correspond to a same the first offset value.
13. The apparatus of claim 12 , wherein a first difference between the first directional mode and the first offset value, a second difference between the second directional mode and the first offset value, and a third difference between the first directional mode and the second directional mode are within a predefined range.
14. The apparatus of claim 13 , wherein the predefined range is equal to or larger than the first offset value minus a constant value, and equal to or smaller than the first offset value plus the constant value.
15. The apparatus of claim 14 , wherein the constant value is one of 1, 2, 3, or 4.
16. The apparatus of claim 10 , wherein the processing circuitry is further configured to:
determine the first reference sample from the reference samples of the first reference line based on a first directional angle, the first directional angle being equal to a sum of the first directional mode of the current block and the first offset value; and
determine the second reference sample from the reference samples of the second reference line based on a second directional angle, the second directional angle being equal to a sum of the second directional mode of the current block and the second offset value.
17. The apparatus of claim 10 , wherein:
when the first directional mode and the second directional mode of the current block are larger than 45 degrees,
a difference of the first offset value and the second offset value is within a preset range.
18. The apparatus of claim 10 , wherein an offset value for a chroma component of the current block is determined based on a reference line of the plurality of reference lines that is associated with a luma component of the current block.
19. A method of processing visual media data, the method comprising:
processing a bitstream that includes the visual media data according to a format rule, wherein
the bitstream includes coded information of a current block and a plurality of reference lines of the current block, each of the plurality of reference lines including a respective row of reference samples above a top side of the current block and a respective column of reference samples at a left side of the current block; and
the format rule specifies that:
(i) a first offset value in an angle-to-offset mapping table and (ii) a second offset value in the angle-to-offset mapping table are determined, the first offset value being associated with a first directional mode for a first reference line of the plurality of reference lines and a second directional mode for a second reference line of the plurality of reference lines, the first reference line being adjacent to the current block and the second reference line being adjacent to the first reference line, the second offset value being associated with the first directional mode for the first reference line of the plurality of reference lines and the second directional mode for the second reference line of the plurality of reference lines;
(i) a first reference sample for a sample of the current block from the first reference line is determined based on the first offset value, and (ii) a second reference sample for the sample of the current block from the second reference line is determined based on the second offset value; and
the sample of the current block is processed based on one of the first reference sample and the second reference sample.
20. The method of claim 19 , wherein:
the angle-to-offset mapping table indicates correlations between candidate directional modes and offset values that are associated with the current block and the first reference line, and
the angle-to-offset mapping table indicates correlations between candidate directional modes and offset values that are associated with the current block and the second reference line.