Chroma mode video coding

1. A method of video decoding, executable by a processor, the method comprising:

receiving video data comprising (1) a chroma component having a first nominal angle and first delta angles and (2) a luma component having a second nominal angle and second delta angles, wherein the first delta angles are dependent on the second delta angles;

parsing or deriving first delta angle values for the first delta angles based at least on an intra prediction mode associated with the luma component, wherein the first delta angle values are derived from one or more nominal angles associated with one or more sample positions corresponding to one or more luma blocks based on semi-decoupled partitioning being applied; and

decoding the video data based on the first delta angle values corresponding to the first delta angles.

2. The method of claim 1 , wherein the first delta angles are set equal to second delta angle values corresponding to the second delta angles based on a chroma intra prediction mode being a directional intra prediction mode and the first nominal angle being equal to the second nominal angle.

3. The method of claim 2 , wherein the first delta angle values are equal to delta angle values of a left or upper neighboring mode of a corresponding luma block based on the first nominal angle being equal to a left or upper neighboring mode of the corresponding luma block and the first nominal angle of the chroma intra prediction mode being not equal to the second nominal angle.

4. The method of claim 1 , wherein the first delta angle values are equal to second delta angle values.

5. The method of claim 1 , wherein the first delta angle values are entropy-coded based on second delta angle values.

6. The method of claim 5 , wherein:

a first flag is signaled to indicate whether a current mode is a chroma-from-luma mode;

a second flag is signaled to indicate whether the current mode is a nominal mode of a corresponding luma block and whether the current mode is a directional mode; and

a third flag is signaled to indicate an index of the first and the second delta angles.

7. The method of claim 1 , the first delta angle values are entropy-coded based on using a delta angle of co-located luma blocks as a context.

8. The method of claim 1 , wherein the first delta angle values are entropy-coded based on using a delta angle of neighboring chroma blocks as a context.

9. The method of claim 1 , wherein an absolute difference between the first delta angle values and second delta angle values corresponding to the second delta angles signals an entropy-coding of a chroma intra prediction mode instead of signaling delta angles of a current chroma block.

10. The method of claim 1 , wherein delta angles of chroma intra prediction mode is signaled in response to the first nominal angle and the second nominal angle being the same or close to each other.

11. The method of claim 10 , wherein the first delta angle values are entropy-coded based on using a delta angle of co-located luma blocks as a context in response to the first nominal angle and the second nominal angle being the same or close to each other, wherein the first nominal angle and the second nominal angle being close to each other when a difference of a nominal angle between chroma block and its corresponding luma block is smaller than 2.

12. A computer system for decoding video data, the computer system comprising:

one or more computer-readable non-transitory storage media configured to store computer program code; and

one or more computer processors configured to access said computer program code and operate as instructed by said computer program code, said computer program code including:

receiving code configured to cause the one or more computer processors to receive video data comprising (1) a chroma component having a first nominal angle and first delta angles and (2) a luma component having a second nominal angle and second delta angles, wherein the first delta angles are dependent on the second delta angles;

parsing or deriving code configured to cause the one or more computer processors to parse or derive first delta angle values for the first delta angles based on at least an intra prediction mode associated with the luma component, wherein the first delta angle values are derived from one or more nominal angles associated with one or more sample positions corresponding to one or more luma blocks based on semi-decoupled partitioning being applied; and

decoding code configured to cause the one or more computer processors to decode the video data based on the first delta angle values corresponding to the first delta angles.

13. The computer system of claim 12 , the first delta angle values are entropy-coded based on using a delta angle of co-located luma blocks as a context.

14. The computer system of claim 12 , wherein the first delta angle values are entropy-coded based on using a delta angle of neighboring chroma blocks as a context.

15. The computer system of claim 12 , wherein an absolute difference between the first delta angle values and second delta angle values corresponding to the second delta angles signals an entropy-coding of a chroma intra prediction mode instead of signaling delta angles of a current chroma block.

16. A non-transitory computer readable medium having stored thereon a computer program for decoding video data, the computer program configured to cause one or more computer processors to:

receive video data comprising (1) a chroma component having a first nominal angle and first delta angles and (2) a luma component having a second nominal angle and second delta angles, wherein the first delta angles are dependent on the second delta angles;

parse or derive first delta angle values for the first delta angles based on at least an intra prediction mode associated with the luma component, wherein the first delta angle values are derived from one or more nominal angles associated with one or more sample positions corresponding to one or more luma blocks based on semi-decoupled partitioning being applied; and

decode the video data based on the first delta angle values corresponding to the first delta angles.

17. The non-transitory computer readable medium of claim 16 , the first delta angle values are entropy-coded based on using a delta angle of co-located luma blocks as a context.

18. The non-transitory computer readable medium of claim 16 , wherein the first delta angle values are entropy-coded based on using a delta angle of neighboring chroma blocks as a context.

19. The non-transitory computer readable medium of claim 16 , wherein an absolute difference between the first delta angle values and second delta angle values corresponding to the second delta angles signals an entropy-coding of a chroma intra prediction mode instead of signaling delta angles of a current chroma block.