Scan-based sliding window in context derivation for transform coefficient coding

1. A method of coding transform coefficients associated with residual video data in a video coding process, the method comprising:

defining a context derivation neighborhood for one of a plurality of transform coefficients using a sliding window that is determined based on a transform coefficient scan order and that includes a set of transform coefficients scanned prior to the one of the plurality of transform coefficients in the transform coefficient scan order, wherein the context derivation neighborhood indicates one or more transform coefficients of the plurality of transform coefficients from which a context is derived;

determining the context for the one of the plurality of transform coefficients based on the context derivation neighborhood; and

coding the one of the plurality of transform coefficients based on the determined context.

2. The method of claim 1 , further comprising moving the sliding window one position in the transform coefficient scan order after coding the one of the plurality of transform coefficients such that the sliding window includes the one of the plurality of transform coefficients.

3. The method of claim 1 , wherein the set of transform coefficients comprises a set of consecutive transform coefficients in the coefficient scan order.

4. The method of claim 1 , wherein the one of the plurality of transform coefficients has a scan order position n, and the context derivation neighborhood comprises transform coefficients at scan order positions n+i to n+j, wherein scan order position n is scanned after scan order positions n+i to n+j, and scan order position n+j is scanned after scan order position n+i.

5. The method of claim 1 , further comprising:

defining context derivation neighborhoods for other transform coefficients of the plurality of transform coefficients based on the transform coefficient scan order,

wherein each of the context derivation neighborhoods corresponds to a sliding window along the scan order relative to the respective coefficient to be coded.

6. The method of claim 1 , wherein defining the context derivation neighborhood for the one of the plurality of transform coefficients comprises including a gap of at least one transform coefficient in the transform coefficient scan order between the one of the plurality of transform coefficients and transform coefficients associated with the context derivation neighborhood.

7. The method of claim 6 , wherein the transform coefficient has a scan order position n, and the context derivation neighborhood comprises transform coefficients at scan order positions n+2 to n+6, wherein scan order position n is scanned after scan order positions n+2 to n+6.

8. The method of claim 1 ,

wherein the plurality of transform coefficients are associated with a sub-block of transform coefficients;

further comprising defining an initial context derivation neighborhood that is not based on the scan order for an initial transform coefficient of the plurality of transform coefficients, wherein the initial transform coefficient is scanned first in the sub-block in the transform coefficient scan order; and

coding the initial transform coefficient based on the initial context derivation neighborhood.

9. The method of claim 1 , wherein the context is a CABAC context, and wherein coding comprises coding the one of the plurality of transform coefficients using a CABAC process.

10. The method of claim 1 , wherein coding the one of the plurality of transform coefficients comprises decoding the one of the plurality of transform coefficients.

11. The method of claim 1 , wherein coding the one of the plurality of transform coefficients comprises encoding the one of the plurality of transform coefficients.

12. An apparatus for coding transform coefficients associated with residual video data in a video coding process, the apparatus comprising one or more processors configured to:

define a context derivation neighborhood for one of a plurality of transform coefficients using a sliding window that is determined based on a transform coefficient scan order and that includes a set of transform coefficients scanned prior to the one of the plurality of transform coefficients in the transform coefficient scan order, wherein the context derivation neighborhood indicates one or more transform coefficients of the plurality of transform coefficients from which a context is derived;

determine the context for the one of the plurality of transform coefficients based on the context derivation neighborhood; and

code the one of the plurality of transform coefficients based on the determined context.

13. The apparatus of claim 12 , wherein the one or more processors are further configured to move the sliding window one position in the transform coefficient scan order after coding the one of the plurality of transform coefficients such that the sliding window includes the one of the plurality of transform coefficients.

14. The apparatus of claim 12 , wherein the set of transform coefficients comprises a set of consecutive transform coefficients in the coefficient scan order.

15. The apparatus of claim 12 , wherein the one of the plurality of transform coefficients has a scan order position n, and the context derivation neighborhood comprises transform coefficients at scan order positions n+i to n+j, wherein scan order position n is scanned after scan order positions n+i to n+j, and scan order position n+j is scanned after scan order position n+i.

16. The apparatus of claim 12 , wherein the one or more processors are further configured to:

define context derivation neighborhoods for other transform coefficients of the plurality of transform coefficients based on the transform coefficient scan order,

wherein each of the context derivation neighborhoods corresponds to a sliding window along the scan order relative to the respective coefficient to be coded.

17. The apparatus of claim 12 , wherein to define the context derivation neighborhood for the one of the plurality of transform coefficients, the one or more processors are configured to include a gap of at least one transform coefficient in the transform coefficient scan order between the one of the plurality of transform coefficients and transform coefficients associated with the context derivation neighborhood.

18. The apparatus of claim 17 , wherein the transform coefficient has a scan order position n, and the context derivation neighborhood comprises transform coefficients at scan order positions n+2 to n+6, wherein scan order position n is scanned after scan order positions n+2 to n+6.

19. The apparatus of claim 12 ,

wherein the plurality of transform coefficients are associated with a sub-block of transform coefficients;

wherein the one or more processors are further configured to define an initial context derivation neighborhood that is not based on the scan order for an initial transform coefficient of the plurality of transform coefficients, wherein the initial transform coefficient is scanned first in the sub-block in the transform coefficient scan order; and

code the initial transform coefficient based on the initial context derivation neighborhood.

20. The apparatus of claim 12 , wherein the context is a CABAC context, and wherein to code, the one or more processors are configured to code the one of the plurality of transform coefficients using a CABAC process.

21. The apparatus of claim 12 , wherein to code the one of the plurality of transform coefficients, the one or more processors are configured to decode the one of the plurality of transform coefficients.

22. The apparatus of claim 12 , wherein to code the one of the plurality of transform coefficients, the one or more processors are configured to encode the one of the plurality of transform coefficients.

23. An apparatus for coding transform coefficients associated with residual video data in a video coding process, the apparatus comprising:

means for defining a context derivation neighborhood for one of a plurality of transform coefficients using a sliding window that is determined based on a transform coefficient scan order and that includes a set of transform coefficients scanned prior to the one of the plurality of transform coefficients in the transform coefficient scan order, wherein the context derivation neighborhood indicates one or more transform coefficients of the plurality of transform coefficients from which a context is derived;

means for determining the context for the one of the plurality of transform coefficients based on the context derivation neighborhood; and

means for coding the one of the plurality of transform coefficients based on the determined context.

24. The apparatus of claim 23 , further comprising means for moving the sliding window one position in the transform coefficient scan order after coding the one of the plurality of transform coefficients such that the sliding window includes the one of the plurality of transform coefficients.

25. The apparatus of claim 23 , wherein the set of transform coefficients comprises a set of consecutive transform coefficients in the coefficient scan order.

26. The apparatus of claim 23 , wherein the one of the plurality of transform coefficients has a scan order position n, and the context derivation neighborhood comprises transform coefficients at scan order positions n+i to n+j, wherein scan order position n is scanned after scan order positions n+i to n+j, and scan order position n+j is scanned after scan order position n+i.

27. The apparatus of claim 23 , further comprising:

means for defining context derivation neighborhoods for other transform coefficients of the plurality of transform coefficients based on the transform coefficient scan order,

wherein each of the context derivation neighborhoods corresponds to a sliding window along the scan order relative to the respective coefficient to be coded.

28. The apparatus of claim 23 , wherein the means for defining the context derivation neighborhood for the one of the plurality of transform coefficients comprises means for including a gap of at least one transform coefficient in the transform coefficient scan order between the one of the plurality of transform coefficients and transform coefficients associated with the context derivation neighborhood.

29. The apparatus of claim 28 , wherein the transform coefficient has a scan order position n, and the context derivation neighborhood comprises transform coefficients at scan order positions n+2 to n+6, wherein scan order position n is scanned after scan order positions n+2 to n+6.

30. The apparatus of claim 23 ,

wherein the plurality of transform coefficients are associated with a sub-block of transform coefficients;

further comprising means for defining an initial context derivation neighborhood that is not based on the scan order for an initial transform coefficient of the plurality of transform coefficients, wherein the initial transform coefficient is scanned first in the sub-block in the transform coefficient scan order; and

means for coding the initial transform coefficient based on the initial context derivation neighborhood.

31. The apparatus of claim 23 , wherein the means for coding the one of the plurality of transform coefficients comprises means for decoding the one of the plurality of transform coefficients.

32. The apparatus of claim 23 , wherein the means for coding the one of the plurality of transform coefficients comprises means for encoding the one of the plurality of transform coefficients.

33. A non-transitory computer-readable medium comprising instructions that, when executed, cause one or more processors to:

define a context derivation neighborhood for one of a plurality of transform coefficients using a sliding window that is determined based on a transform coefficient scan order and that includes a set of transform coefficients scanned prior to the one of the plurality of transform coefficients in the transform coefficient scan order, wherein the context derivation neighborhood indicates one or more transform coefficients of the plurality of transform coefficients from which a context is derived;

determine the context for the one of the plurality of transform coefficients based on the context derivation neighborhood; and

code the one of the plurality of transform coefficients based on the determined context.

34. The computer-readable medium of claim 33 , further comprising instructions that cause the one or more processors to move the sliding window one position in the transform coefficient scan order after coding the one of the plurality of transform coefficients such that the sliding window includes the one of the plurality of transform coefficients.

35. The computer-readable medium of claim 33 , wherein the set of transform coefficients comprises a set of consecutive transform coefficients in the coefficient scan order.

36. The computer-readable medium of claim 33 , wherein the one of the plurality of transform coefficients has a scan order position n, and the context derivation neighborhood comprises transform coefficients at scan order positions n+i to n+j, wherein scan order position n is scanned after scan order positions n+i to n+j, and scan order position n+j is scanned after scan order position n+i.

37. The computer-readable medium of claim 33 , further comprising instructions that cause the one or more processors to:

define context derivation neighborhoods for other transform coefficients of the plurality of transform coefficients based on the transform coefficient scan order,

wherein each of the context derivation neighborhoods corresponds to a sliding window along the scan order relative to the respective coefficient to be coded.

38. The computer-readable medium of claim 33 , wherein to define the context derivation neighborhood for the one of the plurality of transform coefficients, the instructions cause the one or more processors to include a gap of at least one transform coefficient in the transform coefficient scan order between the one of the plurality of transform coefficients and transform coefficients associated with the context derivation neighborhood.

39. The computer-readable medium of claim 38 , wherein the transform coefficient has a scan order position n, and the context derivation neighborhood comprises transform coefficients at scan order positions n+2 to n+6, wherein scan order position n is scanned after scan order positions n+2 to n+6.

40. The computer-readable medium of claim 33 ,

wherein the plurality of transform coefficients are associated with a sub-block of transform coefficients;

further comprising instructions that cause the one or more processors to define an initial context derivation neighborhood that is not based on the scan order for an initial transform coefficient of the plurality of transform coefficients, wherein the initial transform coefficient is scanned first in the sub-block in the transform coefficient scan order; and

code the initial transform coefficient based on the initial context derivation neighborhood.

41. The computer-readable medium of claim 33 , wherein to code the one of the plurality of transform coefficients, the instructions cause the one or more processors to decode the one of the plurality of transform coefficients.

42. The computer-readable medium of claim 33 , wherein to code the one of the plurality of transform coefficients, the instructions cause the one or more processors to encode the one of the plurality of transform coefficients.