Method and apparatus for improved context design for prediction mode and coded block flag (CBF)

1. A method of controlling intra-inter prediction for decoding or encoding of a video sequence, the method being performed by at least one processor, and the method comprising:

determining whether a neighboring block of a current block is coded by an intra prediction mode, an inter prediction mode, or an intra-inter prediction mode;

based on the neighboring block being determined to be coded by the intra-inter prediction mode:

performing intra mode coding of the current block, using the intra prediction mode associated with the intra-inter prediction mode;

incrementing a context index of a prediction mode flag associated with the current block by a first value;

setting a prediction mode flag associated with the neighboring block;

deriving a context value, based on the set prediction mode flag associated with the neighboring block; and

using the derived context value, performing entropy coding of the prediction mode flag associated with the current block that indicates that the current block is intra coded;

based on the neighboring block being determined to be coded by the intra prediction mode, incrementing the context index by a second value different than the first value; and

based on the neighboring block being determined to be coded by the inter prediction mode, incrementing the context index by a third value different than the first value and the second value.

2. The method of claim 1 , further comprising, based on the neighboring block being determined to be coded by the intra-inter prediction mode, performing Most Probable Mode (MPM) derivation of the current block, using the intra prediction mode associated with the intra-inter prediction mode.

3. The method of claim 1 , wherein the intra prediction mode associated with the intra-inter prediction mode is a planar mode.

4. The method of claim 1 , wherein the intra prediction mode associated with the intra-inter prediction mode is a DC mode.

5. The method of claim 1 , wherein the intra prediction mode associated with the intra-inter prediction mode is an intra prediction mode that is applied in the intra-inter prediction mode.

6. The method of claim 1 , wherein the setting the prediction mode flag associated with the neighboring block comprises setting the prediction mode flag associated with the neighboring block to indicate that the neighboring block is intra coded.

7. The method of claim 1 , wherein the setting the prediction mode flag associated with the neighboring block comprising setting the prediction mode flag associated with the neighboring block to indicate that the neighboring block is inter coded.

8. The method of claim 1 , wherein the incrementing the context index comprises:

based on the neighboring block being determined to be coded by the intra prediction mode, incrementing the context index by 2;

based on the neighboring block being determined to be coded by the inter prediction mode, incrementing the context index by 0; and

based on the neighboring block being determined to be coded by the intra-inter prediction mode, incrementing the context index by 1, and

wherein the method further comprises:

determining an average context index, based on the incremented context index and a number of neighboring blocks of the current block; and

setting the prediction mode flag associated with the current block, based on the determined average context index.

9. The method of claim 1 , wherein the incrementing the context index comprises:

based on the neighboring block being determined to be coded by the intra prediction mode, incrementing the context index by 1;

based on the neighboring block being determined to be coded by the inter prediction mode, incrementing the context index by 0; and

based on the neighboring block being determined to be coded by the intra-inter prediction mode, incrementing the context index by 0.5, and

wherein the method further comprises:

determining an average context index, based on the incremented context index and a number of neighboring blocks of the current block; and

setting the prediction mode flag associated with the current block, based on the determined average context index.

10. An apparatus for controlling intra-inter prediction for decoding or encoding of a video sequence, the apparatus comprising:

at least one memory configured to store computer program code; and

at least one processor configured to access the at least one memory and operate according to the computer program code, the computer program code comprising:

first determining code configured to cause the at least one processor to determine whether a neighboring block of a current block is coded by an intra prediction mode, an inter prediction mode, or an intra-inter prediction mode;

performing code configured to cause the at least one processor to, based on the neighboring block being determined to be coded by the intra-inter prediction mode, perform intra mode coding of the current block, using intra prediction mode associated with the intra-inter prediction mode;

incrementing code configured to cause the at least one processor to:

based on the neighboring block being determined to be coded by the intra-inter prediction mode, increment a context index of a prediction mode flag associated with the current block by a first value;

based on the neighboring block being determined to be boded by the intra prediction mode, incrementing the context index by a second value different than the first value; and

based on the neighboring block being determined to be coded by the inter prediction mode, incrementing the context index by a third value different than the first value and the second value; and

setting code configured to cause the at least one processor to, based on the neighboring block being determined to be coded by the intra-inter prediction mode:

set a prediction mode flag associated with the neighboring block;

derive a context value, based on the set prediction mode flag associated with the neighboring block; and

using the derived context value, perform entropy coding of the prediction mode flag associated with the current block that indicates that the current block is intra coded.

11. The apparatus of claim 10 , wherein the performing code is further configured to cause the at least one processor to, based on the neighboring block being determined to be coded by the intra-inter prediction mode, perform Most Probable Mode (MPM) derivation of the current block, using the intra prediction mode associated with the intra-inter prediction mode.

12. The apparatus of claim 10 , wherein the intra prediction mode associated with the intra-inter prediction mode is a planar mode.

13. The apparatus of claim 10 , wherein the intra prediction mode associated with the intra-inter prediction mode is a DC mode.

14. The apparatus of claim 10 , wherein the intra prediction mode associated with the intra-inter prediction mode is an intra prediction mode that is applied in the intra-inter prediction mode.

15. The apparatus of claim 10 , wherein the setting code is further configured to cause the at least one processor to set the prediction mode flag associated with the neighboring block to indicate that the neighboring block is intra coded.

16. The apparatus of claim 10 , wherein the setting code is further configured to cause the at least one processor to set the prediction mode flag associated with the neighboring block to indicate that the neighboring block is inter coded.

17. The apparatus of claim 10 , wherein the incrementing code is further configured to cause the at least one processor to:

based on the neighboring block being determined to be coded by the intra prediction mode, increment the context index by 2;

based on the neighboring block being determined to be coded by the inter prediction mode, increment the context index by 0; and

based on the neighboring block being determined to be coded by the intra-inter prediction mode, increment the context index by 1,

wherein the apparatus further comprises second determining code configured to cause the at least one processor to determine an average context index, based on the incremented context index and a number of neighboring blocks of the current block, and

wherein the setting code is further configured to cause the at least one processor to set the prediction mode flag associated with the current block, based on the determined average context index.

18. The apparatus of claim 10 , wherein the incrementing code is further configured to cause the at least one processor to:

based on the neighboring block being determined to be coded by the intra prediction mode, increment the context index by 1;

based on the neighboring block being determined to be coded by the inter prediction mode, increment the context index by 0; and

based on the neighboring block being determined to be coded by the intra-inter prediction mode, increment the context index by 0.5,

wherein the apparatus further comprises second determining code configured to cause the at least one processor to determine an average context index, based on the incremented context index and a number of neighboring blocks of the current block, and

wherein the setting code is further configured to cause the at least one processor to set the prediction mode flag associated with the current block, based on the determined average context index.

19. A non-transitory computer-readable storage medium storing instructions that cause at least one processor to:

determine whether a neighboring block of a current block is coded by an intra prediction mode, an inter prediction mode, or an intra-inter prediction mode;

based on the neighboring block being determined to be coded by the intra-inter prediction mode:

perform intra mode coding of the current block, using the intra prediction mode associated with the intra-inter prediction mode;

increment a context index of a prediction mode flag associated with the current block by a first value;

set a prediction mode flag associated with the neighboring block;

derive a context value, based on the set prediction mode flag associated with the neighboring block; and

using the derived context value, perform entropy coding of the prediction mode flag associated with the current block that indicates that the current block is intra coded;

based on the neighboring block being determined to be coded by the inter prediction mode, increment the context index by a second value different than the first value; and

based on the neighboring block being determined to be coded by the inter prediction mode, increment the context index by a third value different than the first value and the second value.

20. The non-transitory computer-readable storage medium of claim 19 , wherein the instructions further cause the at least one processor to, based on the neighboring block being determined to be coded by the intra-inter prediction mode, perform Most Probable Mode (MPM) derivation of the current block, using the intra prediction mode associated with the intra-inter prediction mode.