Chroma intra prediction in video coding

1. A method of coding video data, the method comprising:

selecting a set of wide-angle intra prediction directions based on a size of a luma block of a picture having a YUV 4:2:2 chroma sampling format;

determining an intra prediction direction for the luma block, wherein the intra prediction direction for the luma block is in the set of wide-angle intra prediction directions;

determining an intra prediction direction for a chroma block, wherein:

the luma block is collocated in the picture with the chroma block,

the chroma block has a different width/height ratio than the luma block, and

the intra prediction direction for the chroma block is guaranteed to have the intra prediction direction for the luma block;

using the intra prediction direction for the luma block to generate a prediction block for the luma block;

using the intra prediction direction for the chroma block to generate a prediction block for the chroma block;

coding the luma block based on the prediction block for the luma block; and

coding the chroma block based on the prediction block for the chroma block.

2. The method of claim 1 , wherein selecting the set of wide-angle intra prediction directions comprises:

determining a first set of intra prediction directions based on the size of the luma block;

removing the first set of intra prediction directions from a second set of intra prediction directions, wherein the second set of intra prediction directions range from 45 degrees to −135 degrees; and

adding the set of wide-angle intra prediction directions to the second set of intra prediction directions, wherein the wide-angle intra prediction directions make use of mode indexes of the first set of intra prediction directions.

3. The method of claim 2 , wherein:

coding the chroma block comprises encoding the chroma block,

the method further comprises selecting the intra prediction direction for the luma block from the second set of intra prediction directions after adding the set of wide-angle intra prediction directions to the second set of intra prediction directions; and

determining the intra prediction direction for the chroma block comprises determining the intra prediction direction for the chroma block such that the intra prediction direction for the chroma block is the same as the intra prediction direction for the luma block.

4. The method of claim 1 , wherein determining the intra prediction direction for the luma block comprises determining an intra prediction mode indicated by prediction information syntax elements, wherein the intra prediction mode corresponds to the intra prediction direction for the luma block.

5. The method of claim 1 , wherein the set of wide-angle intra prediction directions includes one or more intra prediction directions beyond 45 degrees or beyond −135 degrees.

6. The method of claim 1 , wherein selecting the set of wide-angle intra prediction directions for the chroma block comprises a process of Versatile Video Coding (VVC) to determine the set of wide-angle intra prediction directions based on a derive-from block size.

7. The method of claim 1 , wherein:

coding the luma block comprises decoding the luma block based on the prediction block for the luma block, and

coding the chroma block comprises decoding the chroma block based on the prediction block for the chroma block.

8. The method of claim 7 , wherein:

decoding the luma block based on the prediction block for the luma block comprises reconstructing the luma block based on the prediction block for the luma block and residual data for the luma block, and

decoding the chroma block based on the prediction block for the chroma block comprises reconstructing the chroma block based on the prediction block for the chroma block and residual data for the chroma block.

9. The method of claim 1 , wherein:

coding the luma block comprises encoding the luma block based on the prediction block for the luma block, and

coding the chroma block comprises encoding the chroma block based on the prediction block for the chroma block.

10. The method of claim 9 , wherein:

encoding the luma block comprises generating residual data for the luma block based on samples of the luma block and the prediction block for the luma block, and

encoding the chroma block comprises generating residual data for the chroma block based on samples of the chroma block and the prediction block for the chroma block.

11. A device for coding video data, the device comprising:

a memory to store the video data; and

one or more processors implemented in circuitry, wherein the one or more processors are configured to:

select a set of wide-angle intra prediction directions based on a size of a luma block of a picture having a YUV 4:2:2 chroma sampling format;

determine an intra prediction direction for the luma block, wherein the intra prediction direction for the luma block is in the set of wide-angle intra prediction directions;

determine an intra prediction direction for a chroma block, wherein:

the luma block is collocated in the picture with the chroma block,

the chroma block has a different width/height ratio than the luma block, and

the intra prediction direction for the chroma block is guaranteed to have the intra prediction direction for the luma block;

use the intra prediction direction for the luma block to generate a prediction block for the luma block;

use the intra prediction direction for the chroma block to generate a prediction block for the chroma block;

code the luma block based on the prediction block for the luma block; and

code the chroma block based on the prediction block for the chroma block.

12. The device of claim 11 , wherein to select the set of wide-angle intra prediction directions, the one or more processors are configured to:

determine a first set of intra prediction directions based on the size of the luma block;

remove the first set of intra prediction directions from a second set of intra prediction directions, wherein the second set of intra prediction directions range from 45 degrees to −135 degrees; and

add the set of wide-angle intra prediction directions to the second set of intra prediction directions, wherein the wide-angle intra prediction directions make use of mode indexes of the first set of intra prediction directions.

13. The device of claim 12 , wherein:

the one or more processors are further configured to select the intra prediction direction for the luma block from the second set of intra prediction directions after adding the set of wide-angle intra prediction directions to the second set of intra prediction directions; and

to determine the intra prediction direction for the chroma block, the one or more processors are configured to determine the intra prediction direction for the chroma block such that the intra prediction direction for the chroma block is the same as the intra prediction direction for the luma block.

14. The device of claim 11 , wherein to determine the intra prediction direction for the luma block, the one or more processors determine an intra prediction mode indicated by prediction information syntax elements, wherein the intra prediction mode corresponds to the intra prediction direction for the luma block.

15. The device of claim 11 , wherein the set of wide-angle intra prediction directions includes one or more intra prediction directions beyond 45 degrees or beyond −135 degrees.

16. The device of claim 11 , wherein the one or more processors perform a process of Versatile Video Coding (VVC) to determine the set of wide-angle intra prediction directions based on the derive-from block size.

17. The device of claim 11 , wherein:

the one or more processors decode the luma block based on the prediction block for the luma block, and

the one or more processors decode the chroma block based on the prediction block for the chroma block.

18. The device of claim 17 , wherein:

to decode the luma block based on the prediction block for the luma block, the one or more processors are configured to reconstruct the luma block based on the prediction block for the luma block and residual data for the luma block, and

to decode the chroma block based on the prediction block for the chroma block, the one or more processors are configured to reconstruct the chroma block based on the prediction block for the chroma block and residual data for the chroma block.

19. The device of claim 11 , wherein:

the one or more processors are configured to encode the luma block based on the prediction block for the luma block, and

the one or more processors are configured to encode the chroma block based on the prediction block for the chroma block.

20. The device of claim 19 , wherein:

to encode the luma block, the one or more processors are configured to generate residual data for the luma block based on samples of the luma block and the prediction block for the luma block, and

to encode the chroma block, the one or more processors are configured to generate residual data for the chroma block based on samples of the chroma block and the prediction block for the chroma block.

21. The device of claim 11 , further comprising a display configured to display decoded video data.

22. The device of claim 11 , wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

23. A device for coding video data, the device comprising:

means for selecting a set of wide-angle intra prediction directions based on a size of a luma block of a picture having a YUV 4:2:2 chroma sampling format;

means for determining an intra prediction direction for the luma block, wherein the intra prediction direction for the luma block is in the set of wide-angle intra prediction directions;

means for determining an intra prediction direction for a chroma block, wherein:

the luma block is collocated in the picture with the chroma block,

the chroma block has a different width/height ratio than the luma block, and

the intra prediction direction for the chroma block is guaranteed to have the intra prediction direction for the luma block;

means for using the intra prediction direction for the luma block to generate a prediction block for the luma block;

means for using the intra prediction direction for the chroma block to generate a prediction block for the chroma block;

means for coding the luma block based on the prediction block for the luma block; and

means for coding the chroma block based on the prediction block for the chroma block.

24. A computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to:

select a set of wide-angle intra prediction directions based on a size of a luma block of a picture having a YUV 4:2:2 chroma sampling format;

determine an intra prediction direction for the luma block, wherein the intra prediction direction for the luma block is in the set of wide-angle intra prediction directions;

determine an intra prediction direction for a chroma block, wherein:

the luma block is collocated in the picture with the chroma block,

the chroma block has a different width/height ratio than the luma block,

the intra prediction direction for the chroma block is guaranteed to have the intra prediction direction for the luma block;

use the intra prediction direction for the luma block to generate a prediction block for the luma block;

use the intra prediction direction for the chroma block to generate a prediction block for the chroma block;

code the luma block based on the prediction block for the luma block; and

code the chroma block based on the prediction block for the chroma block.