Device and method for intra-prediction of a prediction block of a video image
A device is configured to select a directional intra-prediction mode from a set of directional intra-prediction modes, wherein each directional intra-prediction mode corresponds to a different intra-prediction angle. Further, the device is configured to select a filter from a set of filters based on the selected directional intra-prediction mode. Further, the device is configured to determine, for a given prediction sample of the prediction block, a reference sample from a set of reference samples based on the selected directional intra-prediction mode, and apply the selected filter to the determined reference sample.
1. A device, comprising:
a non-transitory computer-readable storage medium storing instructions; and
one or more processors in communication with the medium and upon execution of the instructions, configured to:
select a directional intra-prediction mode from a set of directional intra-prediction modes, wherein each directional intra-prediction mode of the set of directional intra-prediction modes corresponds to a different intra-prediction angle;
determine, for a prediction sample of a prediction block, a reference sample from a set of reference samples based on the selected directional intra-prediction mode; and
apply a filter to the determined reference sample, wherein, within a subset of directional intra-prediction modes of the set of directional intra-prediction modes, an angular step between the directional intra-prediction modes is defined in dependence of a filter length of the filter.
2. The device according to claim 1 , wherein the angular step is larger for a larger filter length of the filter and smaller for a smaller filter length of the filter.
3. The device according to claim 1 , wherein the angular step is in a range of 2 to 4 degrees.
4. The device according to claim 1 , wherein the filter length of the filter spans 1 to 7 adjacent reference samples.
5. The device according to claim 1 , wherein the angular step is denoted Δα and is defined by
Δα
=
arctan
N
f
Δ
M
0
wherein N f is the filter length of the filter and ΔM 0 is a number of directional intra-prediction modes in the subset.
6. The device according to claim 1 , wherein the filter length of the filter is selected in dependence of an aspect ratio of the prediction block.
7. The device according to claim 1 , wherein the filter length of the filter is selected in dependence of a height or a width of the prediction block.
8. The device according to claim 1 , wherein the filter performs a smoothing over the determined reference sample and one or more adjacent reference samples according to the filter length, when applied to the determined reference sample.
9. The device according to claim 1 , wherein reference samples of the set of reference samples are arranged in a row of a video image adjacently above and above-right the prediction block, or are arranged in a column of the video image adjacently left and left-under the prediction block.
10. The device according to claim 1 , wherein:
the device is configured for encoding or decoding a video image; or
the device is a video encoder or a video decoder.
11. A method, comprising:
selecting a directional intra-prediction mode from a set of directional intra-prediction modes, wherein each directional intra-prediction mode of the set of directional intra-prediction modes corresponds to a different intra-prediction angle;
determining, for a prediction sample of a prediction block, a reference sample from a set of reference samples based on the selected directional intra-prediction mode; and
applying a filter to the determined reference sample, wherein, within a subset of directional intra-prediction modes of the set of directional intra-prediction modes, an angular step between the directional intra-prediction modes is defined in dependence of a filter length of the filter.
12. The method according to claim 11 , wherein the angular step is larger for a larger filter length of the filter and smaller for a smaller filter length of the filter.
13. The method according to claim 11 , wherein the angular step is in a range of 2 to 4 degrees.
14. The method according to claim 11 , wherein the filter length of the filter spans 1 to 7 adjacent reference samples.
15. The method according to claim 11 , wherein the angular step is denoted Δα and is defined by
Δα
=
arctan
N
f
Δ
M
0
wherein N f is the filter length of the filter and ΔM 0 is the number of directional intra-prediction modes in the subset.
16. The method according to claim 11 , wherein the filter length of the filter is selected in dependence of an aspect ratio of the prediction block.
17. The method according to claim 11 , wherein the filter length of the filter is selected in dependence of a height or a width of the prediction block.
18. The method according to claim 11 , wherein the filter performs a smoothing over the determined reference sample and one or more adjacent reference samples according to the filter length, when applied to the determined reference sample.
19. The method according to claim 11 , wherein reference samples of the set of reference samples are arranged in a row of a video image adjacently above and above-right the prediction block, or are arranged in a column of the video image adjacently left and left-under the prediction block.
20. A non-transitory storage medium storing a bitstream, wherein the bitstream is encoded or decoded by executing a program stored in the non-transitory storage medium to:
select a directional intra-prediction mode from a set of directional intra-prediction modes, wherein each directional intra-prediction mode of the set of directional intra-prediction modes corresponds to a different intra-prediction angle;
determine, for a prediction sample of a prediction block, a reference sample from a set of reference samples based on the selected directional intra-prediction mode; and
apply a filter to the determined reference sample, wherein, within a subset of directional intra-prediction modes of the set of directional intra-prediction modes, an angular step between the directional intra-prediction modes is defined in dependence of a filter length of the filter.