Device and method for intra-prediction

1. A device for intra-predicting a non-square prediction block of a video image, the device comprising:

a non-transitory computer-readable storage medium storing instructions; and

one or more processors in communication with the storage 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 corresponds to a different intra-prediction angle, and the set of directional intra-prediction modes includes extended directional intra-prediction modes only applied to non-square blocks, and wherein at least a value of the extended directional intra-prediction modes is larger than 66;

select a filter from a set of filters based on the selected directional intra-prediction mode;

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.

2. The device according to claim 1 , wherein the one or more processors is configured to:

determine a filter length based on the selected directional intra-prediction mode, and

select as the filter, one filter having at least the determined filter length from the set of filters.

3. The device according to claim 1 , wherein

the set of filters includes filters with different filter lengths that span 1, 3 or 5 adjacent reference samples.

4. The device according to claim 1 , wherein

each filter in the set of filters performs a different smoothing over the determined reference sample and one or more adjacent reference samples, when applied to the determined reference sample.

5. The device according to claim 1 , wherein the one or more processors is configured to:

determine an intra-prediction angle corresponding to the selected directional intra-prediction mode; and

select the filter in dependence of the determined intra-prediction angle.

6. The device according to claim 1 , wherein the one or more processors is configured to:

determine an intra-prediction angle corresponding to the selected directional intra-prediction mode;

specify, for a further prediction sample of the prediction block, a further reference sample from the set of reference samples based on the selected directional intra-prediction mode; and

determine a distance between the determined reference sample and the further reference sample; and

select the filter in dependence of the determined distance.

7. The device according to claim 1 , wherein the one or more processors is configured to:

select a same filter for each directional intra-prediction mode selected from a first subset of the directional intra-prediction modes; and

select a different filter for each directional intra-prediction mode selected from a second subset of the directional intra-prediction modes.

8. The device according to claim 1 , wherein the one or more processors is further configured to:

intra-predict the given prediction sample directly from the determined reference sample;

the selected filter is applied to the determined reference sample before or during the intra-prediction of the given prediction sample.

9. The device according to claim 1 , wherein the one or more processors is further configured to:

generate a transposed reference sample by interpolating the determined reference sample based on the selected directional intra-prediction mode; and

intra-predict the given prediction sample from the transposed reference sample;

the selected filter is applied to the determined reference sample before or during the generation of the transposed reference sample.

10. The device according to claim 9 , wherein the one or more processors is further configured to:

transpose each reference sample in the set of reference samples, wherein a row of reference samples becomes a column of transposed reference samples, and a column of reference samples becomes a row of transposed reference samples.

11. The device according to claim 1 , wherein

the extended directional intra-prediction modes include modes that relate to acute intra-prediction angles.

12. The device according to claim 1 , wherein

the device is configured for encoding or decoding the video image; or

the device is a video encoder or a video decoder.

13. The device according to claim 2 , wherein

when the filter length is 1, a coefficient for the selected filter is [1]; or

when the filter length is 3, coefficients for the selected filter is [1, 2, 1].

14. A method for intra-predicting a non-square prediction block of a video image, the method comprising:

selecting 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, and the set of directional intra-prediction modes includes extended directional intra-prediction modes only applied to non-square blocks, and wherein at least a value of the extended directional intra-prediction modes is larger than 66;

selecting a filter from a set of filters based on the selected directional intra-prediction mode;

determining, 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

applying the selected filter to the determined reference sample.

15. The method of claim 14 , wherein

the set of filters includes filters with different filter lengths that span 1, 3 or 5 adjacent reference samples.

16. The method of claim 15 , wherein

when the filter length is 1, a coefficient for the selected filter is [1]; or

when the filter length is 3, coefficients for the selected filter is [1, 2, 1].

17. A method for intra-predicting a non-square prediction block of a video image, the method comprising:

selecting 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, and the set of directional intra-prediction modes includes extended directional intra-prediction modes only applied to non-square blocks, and wherein at least a value of the extended directional intra-prediction modes is larger than 66;

determining, 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

determining whether to apply a filter to the determined reference sample based on the selected directional intra-prediction mode.

18. The method of claim 17 , wherein when determining not to apply the filter to the determined reference sample, a coefficient for the filter is [1]; or

when determining to apply the filter to the determined reference sample, coefficients for the filter is [1, 2, 1].

19. The method of claim 17 , wherein the extended directional intra-prediction modes include modes that relate to acute intra-prediction angles.

20. The method of claim 17 , wherein determining whether to apply the filter to the determined reference sample comprises:

determining a filter length based on the selected directional intra-prediction mode, and

when the filter length is 1, determining not to apply the filter to the determined reference sample; or when the filter length is 3, determining to apply the filter to the determined reference sample.