Indicating intra-prediction mode selection for video coding

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

determining a first most probable intra-prediction mode and a second most probable intra-prediction mode for a coded block of video data based on a context for the current block;

receiving an entropy encoded codeword corresponding to a modified intra-prediction mode index;

determining an intra-prediction mode index based on the modified intra-prediction mode index, an intra-prediction mode index for the first most probable intra-prediction mode, and an intra-prediction mode index for the second most probable intra-prediction mode;

selecting an intra-prediction mode other than the first most probable intra-prediction mode and second most probable intra-prediction mode to use to decode the coded block, wherein the selected intra-prediction mode corresponds to the determined intra-prediction mode index, wherein each of the intra-prediction modes corresponds to a respective intra-prediction mode index, and

when the modified intra-prediction mode index plus one is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and greater than or equal to the intra-prediction mode index for the second most probable intra-prediction mode, selecting the intra-prediction mode comprises selecting the intra-prediction mode corresponding to an intra-prediction mode index that is two greater than the modified intra-prediction mode index,

when the modified intra-prediction mode index is less than the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, selecting the intra-prediction mode comprises selecting the intra-prediction mode having an intra-prediction mode index equal to the modified intra-prediction mode index, and

when the modified intra-prediction mode index plus one is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, selecting the intra-prediction mode comprises selecting the intra-prediction mode corresponding to an intra-prediction mode index that is one greater than the modified intra-prediction mode index; and

decoding the current block using the selected intra-prediction mode.

2. The method of claim 1 , further comprising determining the context for the current block based at least in part on intra-prediction modes for at least one of a left-neighboring block to the current block and an above-neighboring block to the current block.

3. The method of claim 1 , further comprising determining the context for the current block based at least in part on a size of the coded block.

4. The method of claim 1 , further comprising:

determining a third most probable intra-prediction mode.

5. An apparatus for decoding video data, the apparatus comprising a video decoder configured to determine a first most probable intra-prediction mode and a second most probable intra-prediction mode for a coded block of video data based on a context for the current block; receive an entropy encoded codeword corresponding to a modified intra-prediction mode index; determine an intra-prediction mode index based on the modified intra-prediction mode index, an intra-prediction mode index for the first most probable intra-prediction mode, and an intra-prediction mode index for the second most probable intra-prediction mode; select an intra-prediction mode other than the first most probable intra-prediction mode and second most probable intra-prediction mode to use to decode the coded block, wherein the selected intra-prediction mode corresponds to the determined intra-prediction mode index, wherein each of the intra-prediction modes corresponds to a respective intra-prediction mode index, and wherein when the modified intra-prediction mode index plus one is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and greater than or equal to the intra-prediction mode index for the second most probable intra-prediction mode, the video decoder selects the intra-prediction mode by selecting the intra-prediction mode corresponding to an intra-prediction mode index that is two greater than the modified intra-prediction mode index, when the modified intra-prediction mode index is less than the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, the video decoder selects the intra-prediction mode by selecting the intra-prediction mode having an intra-prediction mode index equal to the modified intra-prediction mode index, and when the modified intra-prediction mode index plus one is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, the video decoder selects the intra-prediction mode by selecting the intra-prediction mode corresponding to an intra-prediction mode index that is one greater than the modified intra-prediction mode index; and decode the current block using the selected intra-prediction mode.

6. The apparatus of claim 5 , wherein the video decoder is further configured to determine the context for the current block based at least in part on intra-prediction modes for at least one of a left-neighboring block to the current block and an above-neighboring block to the current block.

7. The apparatus of claim 5 , wherein the video decoder is further configured to determine the context for the current block based at least in part on a size of the coded block.

8. The apparatus of claim 5 , wherein the apparatus comprises at least one of:

an integrated circuit;

a microprocessor; and

a wireless communication device that includes the video decoder.

9. The apparatus of claim 5 , wherein the video decoder is further configured to determine a third most probable intra-prediction mode.

10. A method of encoding video data, the method comprising:

determining a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on an encoding context for the current block;

encoding the current block using an intra-prediction mode other than the first most probable intra-prediction mode and the second most probable intra-prediction mode;

determining an intra-prediction mode index that corresponds to the intra-prediction mode;

determining a modified intra-prediction mode index based on the determined intra-prediction mode index, an intra-prediction mode index for the first most probable intra-prediction mode, an intra-prediction mode index for the second most probable intra-prediction mode, wherein each of the intra-prediction modes corresponds to a respective mode index, and wherein determining the modified intra-prediction mode index comprises:

when the determined intra-prediction mode index is greater than the intra-prediction mode index for the first most probable intra-prediction mode and greater than the intra-prediction mode index for the second most probable intra-prediction mode, determining the modified intra-prediction mode index comprises determining one of the modified intra-prediction mode indexes that is two less than the intra-prediction mode index,

when the intra-prediction mode index is less than the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, determining the modified intra-prediction mode index comprises determining one of the modified intra-prediction mode indexes that is equal to the intra-prediction mode index,

when the intra-prediction mode index is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, determining the modified intra-prediction mode index comprises determining one of the modified intra-prediction mode indexes that is one less than the intra-prediction mode index; and,

outputting an entropy encoded codeword from the table of codewords, wherein the codeword corresponds to the modified intra-prediction mode index.

11. The method of claim 10 , further comprising determining the encoding context for the current block based at least in part on modes for at least one of a left-neighboring block to the current block and an above-neighboring block to the current block.

12. The method of claim 10 , further comprising determining the encoding context for the current block based at least in part on a size of the current block.

13. The method of claim 10 , further comprising:

determining a third most probable intra-prediction mode.

14. An apparatus for encoding video data, the apparatus comprising a video encoder configured to determine a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on an encoding context for the current block; encode the current block using an intra-prediction mode other than the first most probable intra-prediction mode and the second most probable intra-prediction mode; determine an intra-prediction mode index that corresponds to the intra-prediction mode; determine a modified intra-prediction mode index based on the determined intra-prediction mode index, an intra-prediction mode index for the first most probable intra-prediction mode, an intra-prediction mode index for the second most probable intra-prediction mode, wherein each of the intra-prediction modes corresponds to a respective mode index, and wherein when the determined intra-prediction mode index is greater than the intra-prediction mode index for the first most probable intra-prediction mode and greater than the intra-prediction mode index for the second most probable intra-prediction mode, the video encoder determines the modified intra-prediction mode index by determining one of the modified intra-prediction mode indexes that is two less than the intra-prediction mode index, when the intra-prediction mode index is less than the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, the video encoder determines the modified intra-prediction mode index by determining one of the modified intra-prediction mode indexes that is equal to the intra-prediction mode index, when the intra-prediction mode index is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, the video encoder determines the modified intra-prediction mode index by determining one of the modified intra-prediction mode indexes that is one less than the intra-prediction mode index; and output an entropy encoded codeword from the selected table of codewords, wherein the codeword corresponds to the modified intra-prediction mode index.

15. The apparatus of claim 14 , wherein the video encoder is further configured to determine the encoding context for the current block based at least in part on modes for at least one of a left-neighboring block to the current block and an above-neighboring block to the current block.

16. The apparatus of claim 14 , wherein the video encoder is further configured to determine the encoding context for the current block based at least in part on a size of the current block.

17. The apparatus of claim 14 , wherein the apparatus comprises at least one of:

an integrated circuit;

a microprocessor; and

a wireless communication device that includes the video encoder.

18. The apparatus of claim 14 , wherein the video decoder is further configured to determine a third most probable intra-prediction mode.

19. An apparatus for decoding video data, the apparatus comprising:

means for determining a first most probable intra-prediction mode and a second most probable intra-prediction mode for a coded block of video data based on a context for the current block;

means for receiving an entropy encoded codeword corresponding to a modified intra-prediction mode index;

means for determining an intra-prediction mode index based on the modified intra-prediction mode index, an intra-prediction mode index for the first most probable intra-prediction mode, and an intra-prediction mode index for the second most probable intra-prediction mode;

means for selecting an intra-prediction mode other than the first most probable intra-prediction mode and second most probable intra-prediction mode to use to decode the coded block, wherein the selected intra-prediction mode corresponds to the determined intra-prediction mode index, wherein each of the intra-prediction modes corresponds to a respective intra-prediction mode index, and

when the modified intra-prediction mode index plus one is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and greater than or equal to the intra-prediction mode index for the second most probable intra-prediction mode, the means for selecting the intra-prediction mode comprises means for selecting the intra-prediction mode corresponding to an intra-prediction mode index that is two greater than the modified intra-prediction mode index,

when the modified intra-prediction mode index is less than the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, the means for selecting the intra-prediction mode comprises means for selecting the intra-prediction mode having an intra-prediction mode index equal to the modified intra-prediction mode index,

when the modified intra-prediction mode index plus one is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, the means for selecting the intra-prediction mode comprises means for selecting the intra-prediction mode corresponding to an intra-prediction mode index that is one greater than the modified intra-prediction mode index; and

means for decoding the current block using the selected intra-prediction mode.

20. The apparatus of claim 19 , further comprising:

means for determining the context for the current block based at least in part on intra-prediction modes for at least one of a left-neighboring block to the current block and an above-neighboring block to the current block.

21. The apparatus of claim 19 , further comprising:

means for determining the context for the current block based at least in part on a size of the coded block.

22. The apparatus of claim 19 , further comprising:

means for determining a third most probable intra-prediction mode.

23. An apparatus for encoding video data, the apparatus comprising:

means for determining a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on an encoding context for the current block;

means for encoding the current block using an intra-prediction mode other than the first most probable intra-prediction mode and the second most probable intra-prediction mode;

means for determining an intra-prediction mode index that corresponds to the intra-prediction mode;

means for determining a modified intra-prediction mode index based on the determined intra-prediction mode index, an intra-prediction mode index for the first most probable intra-prediction mode, an intra-prediction mode index for the second most probable intra-prediction mode, wherein each of the intra-prediction modes corresponds to a respective mode index, and wherein the means for determining the modified intra-prediction mode index comprises:

when the determined intra-prediction mode index is greater than the intra-prediction mode index for the first most probable intra-prediction mode and greater than the intra-prediction mode index for the second most probable intra-prediction mode, the means for determining the modified intra-prediction mode index comprises means for determining one of the modified intra-prediction mode indexes that is two less than the intra-prediction mode index,

when the intra-prediction mode index is less than the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, the means for determining the modified intra-prediction mode index comprises means for determining one of the modified intra-prediction mode indexes that is equal to the intra-prediction mode index,

when the intra-prediction mode index is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, the means for determining the modified intra-prediction mode index comprises means for determining one of the modified intra-prediction mode indexes that is one less than the intra-prediction mode index; and,

means for outputting an entropy encoded codeword from the selected table of codewords, wherein the codeword corresponds to the modified intra-prediction mode index.

24. The apparatus of claim 23 , further comprising:

means for determining the encoding context for the current block based at least in part on modes for at least one of a left-neighboring block to the current block and an above-neighboring block to the current block.

25. The apparatus of claim 23 , further comprising:

means for determining the encoding context for the current block based at least in part on a size of the current block.

26. The apparatus of claim 23 , further comprising:

means for determining a third most probable intra-prediction mode.

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

determine a first most probable intra-prediction mode and a second most probable intra-prediction mode for a coded block of video data based on a context for the current block;

receive an entropy encoded codeword corresponding to a modified intra-prediction mode index;

determine an intra-prediction mode index based on the modified intra-prediction mode index, an intra-prediction mode index for the first most probable intra-prediction mode, and an intra-prediction mode index for the second most probable intra-prediction mode;

select an intra-prediction mode other than the first most probable intra-prediction mode and second most probable intra-prediction mode to use to decode the coded block, wherein the selected intra-prediction mode corresponds to the determined intra-prediction mode index, wherein each of the intra-prediction modes corresponds to a respective intra-prediction mode index, and

when the modified intra-prediction mode index plus one is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and greater than or equal to the intra-prediction mode index for the second most probable intra-prediction mode, the one or more processors select the intra-prediction mode by selecting the intra-prediction mode corresponding to an intra-prediction mode index that is two greater than the modified intra-prediction mode index,

when the modified intra-prediction mode index is less than the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, the one or more processors select the intra-prediction mode by selecting the intra-prediction mode having an intra-prediction mode index equal to the modified intra-prediction mode index, and

when the modified intra-prediction mode index plus one is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, the one or more processors select the intra-prediction mode by selecting the intra-prediction mode corresponding to an intra-prediction mode index that is one greater than the modified intra-prediction mode index; and

decode the current block using the selected intra-prediction mode.

28. The non-transitory computer-readable storage medium of claim 27 having stored thereon instructions that when executed cause the one or more processors to:

determine a third most probable intra-prediction mode.

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

determine a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on an encoding context for the current block;

encode the current block using an intra-prediction mode other than the first most probable intra-prediction mode and the second most probable intra-prediction mode;

determine an intra-prediction mode index that corresponds to the intra-prediction mode;

determine a modified intra-prediction mode index based on the determined intra-prediction mode index, an intra-prediction mode index for the first most probable intra-prediction mode, an intra-prediction mode index for the second most probable intra-prediction mode, wherein each of the intra-prediction modes corresponds to a respective mode index, and wherein the one or more processors determine the modified intra-prediction mode index by:

when the determined intra-prediction mode index is greater than the intra-prediction mode index for the first most probable intra-prediction mode and greater than the intra-prediction mode index for the second most probable intra-prediction mode, the one or more processors determine the modified intra-prediction mode index by determining one of the modified intra-prediction mode indexes that is two less than the intra-prediction mode index,

when the intra-prediction mode index is less than the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, the one or more processors determine the modified intra-prediction mode index by determining one of the modified intra-prediction mode indexes that is equal to the intra-prediction mode index,

when the intra-prediction mode index is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, the one or more processors determine the modified intra-prediction mode index by determining one of the modified intra-prediction mode indexes that is one less than the intra-prediction mode index; and

output an entropy encoded codeword from the selected table of codewords, wherein the codeword corresponds to the modified intra-prediction mode index.

30. The non-transitory computer-readable storage medium of claim 29 having stored thereon instructions that when executed cause the one or more processors to:

determine a third most probable intra-prediction mode.