Hardware friendly design for intra mode coding

1. A method for intra prediction mode coding in video decoding, the method comprising:

receiving, by a device comprising a memory storing instructions and a processor in communication with the memory, a coded video bitstream;

constructing, by the device, a list of intra modes for a block in the coded video bitstream according to a pre-defined rule based on a size of the block;

dividing, by the device, the list of intra modes into a plurality of intra mode sets for the block;

extracting, by the device from the coded video bitstream, a set index indicating an intra mode set from the plurality of intra mode sets;

extracting, by the device, from the coded video bitstream, a mode index indicating an intra prediction mode from the intra mode set;

determining, by the device, the intra prediction mode for the block based on the set index and the mode index; and

decoding, by the device, the coded video bitstream based on the intra prediction mode, wherein:

when the size of the block is equal to or greater than a first threshold:

the list of intra modes comprises a first sub-list being at a top of the list, and

the first sub-list comprises all non-directional intra prediction modes.

2. The method according to claim 1 , wherein:

the first threshold is 8×8; or

the first threshold is 32 in a number of samples.

3. The method according to claim 1 , wherein:

when a neighboring block uses a directional intra prediction mode and when the size of the block is equal to or greater than the first threshold:

the list of intra modes comprises a second sub-list being next to the first sub-list in the list; and

the second sub-list comprises multiple derived intra prediction modes based on the directional intra prediction mode of the neighboring block.

4. The method according to claim 3 , wherein:

the multiple derived intra prediction modes comprises nine directional intra prediction modes by adding an offset of [0, −1, +1, −2, +2, −3, +3, −4, +4] to the directional intra prediction mode of the neighboring block.

5. The method according to claim 3 , wherein:

the list of intra modes comprises a third sub-list being next to the second sub-list in the list; and

the third sub-list comprises default intra prediction modes.

6. The method according to claim 5 , wherein:

the default intra prediction modes comprises at least one nominal directional intra prediction modes with zero delta angle.

7. The method according to claim 1 , wherein:

when the size of the block is smaller than the first threshold:

the list of intra modes comprises the first sub-list being at a top of the list; and

the first sub-list comprises all non-directional intra prediction modes.

8. The method according to claim 7 , wherein:

the list of intra modes comprises a second sub-list being next to the first sub-list in the list; and

the second sub-list comprises default intra prediction modes.

9. A method of intra prediction mode coding in video encoding, the method comprising:

receiving, by a device comprising a memory storing instructions and a processor in communication with the memory, video data;

constructing, by the device, a list of intra modes for a block in the video data according to a pre-defined rule based on a size of the block;

dividing, by the device, the list of intra modes into a plurality of intra mode sets for the block;

determining, by the device, a set index indicating an intra mode set from the plurality of intra mode sets;

encoding, by the device, the set index into a coded video bitstream;

determining, by the device, a mode index indicating an intra prediction mode from the intra mode set;

encoding, by the device, the mode index into the coded video bitstream;

determining, by the device, the intra prediction mode for the block based on the set index and the mode index; and

encoding, by the device, the block into the coded video bitstream based on the intra prediction mode,

wherein:

when the size of the block is equal to or greater than a first threshold:

the list of intra modes comprises a first sub-list being at a top of the list, and

the first sub-list comprises all non-directional intra prediction modes.

10. The method according to claim 9 , wherein:

the first threshold is 8×8; or

the first threshold is 32 in a number of samples.

11. The method according to claim 9 , wherein:

when a neighboring block uses a directional intra prediction mode and when the size of the block is equal to or greater than the first threshold:

the list of intra modes comprises a second sub-list being next to the first sub-list in the list; and

the second sub-list comprises multiple derived intra prediction modes based on the directional intra prediction mode of the neighboring block.

12. The method according to claim 11 , wherein:

the multiple derived intra prediction modes comprises nine directional intra prediction modes by adding an offset of [0, −1, +1, −2, +2, −3, +3, −4, +4] to the directional intra prediction mode of the neighboring block.

13. The method according to claim 11 , wherein:

the list of intra modes comprises a third sub-list being next to the second sub-list in the list; and

the third sub-list comprises default intra prediction modes.

14. The method according to claim 13 , wherein:

the default intra prediction modes comprises at least one nominal directional intra prediction modes with zero delta angle.

15. The method according to claim 9 , wherein:

when the size of the block is smaller than the first threshold:

the list of intra modes comprises the first sub-list being at a top of the list; and

the first sub-list comprises all non-directional intra prediction modes.

16. The method according to claim 15 , wherein:

the list of intra modes comprises a second sub-list being next to the first sub-list in the list; and

the second sub-list comprises default intra prediction modes.

17. A method of processing video data, the method comprising:

performing, by a device comprising a memory storing instructions and a processor in communication with the memory, a conversion between video data and a bitstream by:

constructing, by the device, a list of intra modes for a block in the video data according to a pre-defined rule based on a size of the block;

dividing, by the device, the list of intra modes into a plurality of intra mode sets for the block;

determining, by the device, a set index indicating an intra mode set from the plurality of intra mode sets;

encoding, by the device, the set index into the bitstream;

determining, by the device, a mode index indicating an intra prediction mode from the intra mode set;

encoding, by the device, the mode index into the bitstream;

determining, by the device, the intra prediction mode for the block based on the set index and the mode index; and

encoding, by the device, the block into the bitstream based on the intra prediction mode,

wherein:

when the size of the block is equal to or greater than a first threshold:

the list of intra modes comprises a first sub-list being at a top of the list, and

the first sub-list comprises all non-directional intra prediction modes.

18. The method according to claim 17 , wherein:

the first threshold is 8×8; or

the first threshold is 32 in a number of samples.

19. The method according to claim 17 , wherein:

when a neighboring block uses a directional intra prediction mode and when the size of the block is equal to or greater than the first threshold:

the list of intra modes comprises a second sub-list being next to the first sub-list in the list; and

the second sub-list comprises multiple derived intra prediction modes based on the directional intra prediction mode of the neighboring block.

20. The method according to claim 19 , wherein:

the multiple derived intra prediction modes comprises nine directional intra prediction modes by adding an offset of [0, −1, +1, −2, +2, −3, +3, −4, +4] to the directional intra prediction mode of the neighboring block.