Deriving context for last position coding for video coding
In one example, a device includes a video coder configured to determine a context for entropy coding a bin of a value indicative of a last significant coefficient of a block of video data using a function of an index of the bin, and code the bin using the determined context. The video coder may encode or decode the bin using context-adaptive binary arithmetic coding (CABAC). The function may also depend on a size of the block. In this manner, a table indicating context indexes for the contexts need not be stored by the device.
1. A method of coding video data, the method comprising:
determining a context for entropy coding a bin of a value indicative of a last significant coefficient of a block of video data using a function of an index of the bin,
wherein the function produces a context index for the context by right-shifting the index of the bin by a value k and adding the right-shifted value to an offset value,
wherein the offset value is determined according to the formula:
offset=3*n+((n+1)>>2),
wherein the value k is determined according to the formula:
k=(n+3)>>2,
wherein the value n is determined according to the formula:
n=(log 2 (block_size)−2), and
wherein the value block_size comprises a value indicative of the size of the block; and
coding the bin using the determined context.
2. The method of claim 1 , wherein determining the context comprises executing the function.
3. The method of claim 1 , wherein the function comprises a linear function.
4. The method of claim 1 , wherein the function comprises a non-linear function.
5. The method of claim 1 , wherein the function produces a context index for the context by right-shifting the index of the bin by one.
6. The method of claim 1 , further comprising receiving the function from a user.
7. The method of claim 1 , further comprising receiving syntax data defining the function.
8. The method of claim 1 , wherein coding the bin comprises entropy decoding encoded data using the determined context to reproduce a value for the bin.
9. The method of claim 1 , wherein coding the bin comprises entropy encoding the bin using the determined context.
10. A device for coding video data, the device comprising:
a memory configured to store the video data; and
one or more processors configured to:
determine a context for entropy coding a bin of a value indicative of a last significant coefficient of a block of video data using a function of an index of the bin,
wherein the function produces a context index for the context by right-shifting the index of the bin by a value k and adding the right-shifted value to an offset value,
wherein the offset value is determined according to the formula:
offset=3*n+((n+1)>>2),
wherein the value k is determined according to the formula:
k=(n+3)>>2,
wherein the value n is determined according to the formula:
n=(log 2 (block_size)−2), and
wherein the value block_size comprises a value indicative of the size of the block; and
code the bin using the determined context.
11. The device of claim 10 , wherein the video coder is configured to determine the context at least in part by executing the function.
12. The device of claim 10 , wherein the video coder is further configured to receive syntax data defining the function.
13. The device of claim 10 , wherein the video coder is configured to code the bin at least in part by entropy decoding encoded data using the determined context to reproduce a value for the bin.
14. The device of claim 10 , wherein the video coder is configured to code the bin at least in part by entropy encoding the bin using the determined context.
15. The device of claim 10 , wherein the device comprises at least one of:
an integrated circuit;
a microprocessor; and
a wireless communication device that comprises the video coder.
16. A device for coding video data, the device comprising:
means for determining a context for entropy coding a bin of a value indicative of a last significant coefficient of a block of video data using a function of an index of the bin,
wherein the function produces a context index for the context by right-shifting the index of the bin by a value k and adding the right-shifted value to an offset value,
wherein the offset value is determined according to the formula:
offset=3*n+((n+1)>>2),
wherein the value k is determined according to the formula:
k=(n+3)>>2,
wherein the value n is determined according to the formula:
n=(log 2 (block_size)−2), and
wherein the value block_size comprises a value indicative of the size of the block; and
means for coding the bin using the determined context.
17. The device of claim 16 , wherein the means for determining the context comprises means for executing the function.
18. The device of claim 16 , further comprising means for receiving syntax data defining the function.
19. A computer-readable storage medium encoded with instructions that, when executed, cause a programmable processor of a computing device to:
determine a context for entropy coding a bin of a value indicative of a last significant coefficient of a block of video data using a function of an index of the bin,
wherein the function produces a context index for the context by right-shifting the index of the bin by a value k and adding the right-shifted value to an offset value,
wherein the offset value is determined according to the formula:
offset=3*n+((n+1)>>2),
wherein the value k is determined according to the formula:
k=(n+3)>>2,
wherein the value n is determined according to the formula:
n=(log 2 (block_size)−2), and
wherein the value block_size comprises a value indicative of the size of the block; and
code the bin using the determined context.
20. The computer-readable storage medium of claim 19 , wherein the instructions that cause the programmable processor to determine the context further include instructions that cause the programmable processor to execute the function.
21. The computer-readable storage medium of claim 19 , further encoded with instructions that, when executed, cause the programmable processor to receive syntax data defining the function.