Predictive geometry coding in G-PCC

1. A method of encoding a point cloud, the method comprising:

obtaining a value of a secondary residual for geometry coding a current predictive tree node of the point cloud; and

encoding the value of the secondary residual, wherein encoding the value comprises:

encoding, using a first set of context-adaptive binary arithmetic coding (CABAC) contexts, prefix bins of a syntax element, the syntax element having a value that specifies an absolute value of the value of the secondary residual; and

encoding, using a second set of CABAC contexts that is different than the first set of contexts, suffix bins of the syntax element.

2. The method of claim 1 , wherein the syntax element comprises a ptn_sec_residual_abs_minus2 syntax element.

3. The method of claim 1 , wherein the absolute value of the secondary residual is greater than 17, and wherein encoding the value of the secondary residual does not include encoding a syntax element that specifies the absolute value of the secondary residual minus 17.

4. The method of claim 1 , wherein the first set of CABAC contexts comprises CABAC contexts having context indices between 0 and a−1, and wherein the second set of CABAC contexts comprises CABAC contexts having context indices between a and a+b−1.

5. The method of claim 4 , wherein a is 5, and wherein b is 4.

6. The method of claim 1 , wherein the syntax element comprises a first syntax element, and wherein encoding the value of the secondary residual further comprises:

encoding a second syntax element having a value that specifies whether the value of the secondary residual is equal to zero;

where the value of the secondary residual is not equal to zero:

encoding a third syntax element having a value that specifies a sign of the value of the secondary residual; and

encoding a fourth syntax element having a value that specifies whether the value of the secondary residual is greater than one;

where the value of the secondary residual is greater than one, encoding the first syntax element.

7. The method of claim 1 , wherein the current predictive tree node is a first predictive tree node, wherein the syntax element comprises a first syntax element, the method further comprising:

obtaining a value of a phi multiplier for geometry coding a second predictive tree node of the point cloud; and

encoding the value of the phi multiplier, wherein encoding the value of the phi multiplier comprises:

encoding a fifth syntax element having a value that specifies an absolute value of the value of the phi multiplier minus 9.

8. The method of claim 7 , wherein the absolute value of the phi multiplier is greater than 17, and wherein encoding the value of the phi multiplier does not include encoding a syntax element that specifies the value of the phi multiplier minus 17.

9. The method of claim 1 , wherein the current predictive tree node is a first predictive tree node, and wherein the syntax element comprises a first syntax element, the method further comprising:

encoding, using variable length coding, a sixth syntax element having a value that represents a number of direct child nodes of a second predictive tree node that are present in a geometry predictive tree that represents the point cloud.

10. The method of claim 9 , wherein the sixth syntax element that represents the number of direct child nodes of the second predictive tree node present in the geometry predictive tree comprises a ptn_child_cnt syntax element.

11. The method of claim 9 , wherein encoding the sixth syntax element using variable length coding comprises utilizing a shorter codeword where the number of direct child nodes is 1 than where the number of direct child nodes is 0.

12. A method of decoding a point cloud, the method comprising:

obtaining a value of a secondary residual for geometry coding a current predictive tree node of the point cloud; and

decoding the value of the secondary residual, wherein encoding the value comprises:

decoding, using a first set of context-adaptive binary arithmetic coding (CABAC) contexts, prefix bins of a syntax element, the syntax element having a value that specifies an absolute value of the value of the secondary residual; and

decoding, using a second set of CABAC contexts that is different than the first set of contexts, suffix bins of the syntax element.

13. The method of claim 12 , wherein the syntax element comprises a ptn_sec_residual_abs_minus2 syntax element.

14. The method of claim 12 , wherein the absolute value of the secondary residual is greater than 17, and wherein decoding the value of the secondary residual does not include decoding a syntax element that specifies the absolute value of the secondary residual minus 17.

15. The method of claim 12 , wherein the first set of CABAC contexts comprises CABAC contexts having context indices between 0 and a−1, and wherein the second set of CABAC contexts comprises CABAC contexts having context indices between a and a+b−1.

16. The method of claim 15 , wherein a is 5, and wherein b is 4.

17. The method of claim 12 , wherein the syntax element comprises a first syntax element, and wherein decoding the value of the secondary residual further comprises:

decoding a second syntax element having a value that specifies whether the value of the secondary residual is equal to zero;

where the value of the secondary residual is not equal to zero:

decoding a third syntax element having a value that specifies a sign of the value of the secondary residual; and

decoding a fourth syntax element having a value that specifies whether the value of the secondary residual is greater than one;

where the value of the secondary residual is greater than one, decoding the first syntax element.

18. The method of claim 12 , wherein the current predictive tree node is a first predictive tree node, wherein the syntax element comprises a first syntax element, the method further comprising:

obtaining a value of a phi multiplier for geometry coding a second predictive tree node of the point cloud; and

decoding the value of the phi multiplier, wherein decoding the value of the phi multiplier comprises:

decoding a fifth syntax element having a value that specifies an absolute value of the value of the phi multiplier minus 9.

19. The method of claim 18 , wherein the absolute value of the phi multiplier is greater than 17, and wherein decoding the value of the phi multiplier does not include decoding a syntax element that specifies the value of the phi multiplier minus 17.

20. The method of claim 12 , wherein the current predictive tree node is a first predictive tree node, wherein the syntax element comprises a first syntax element, the method further comprising:

decoding, using variable length coding, a sixth syntax element having a value that represents a number of direct child nodes of a second predictive tree node that are present in a geometry predictive tree that represents the point cloud.

21. The method of claim 20 , wherein the sixth syntax element that represents the number of direct child nodes of the second predictive tree node present in the geometry predictive tree comprises a ptn_child_cnt syntax element.

22. The method of claim 20 , wherein decoding the sixth syntax element using variable length coding comprises utilizing a shorter codeword where the number of direct child nodes is 1 than where the number of direct child nodes is 0.

23. A device for encoding a point cloud, the device comprising:

a memory configured to store at least a portion of the point cloud; and

one or more processors implemented in circuitry and configured to:

obtain a value of a secondary residual for geometry coding a current predictive tree node of the point cloud; and

encode the value of the secondary residual, wherein, to encode the value, the one or more processors are configured to:

encode, using a first set of context-adaptive binary arithmetic coding (CABAC) contexts, prefix bins of a syntax element, the syntax element having a value that specifies an absolute value of the value of the secondary residual; and

encode, using a second set of CABAC contexts that is different than the first set of contexts, suffix bins of the syntax element.

24. The device of claim 23 , wherein the syntax element comprises a ptn_sec_residual_abs_minus2 syntax element.

25. The device of claim 23 , wherein the absolute value of the secondary residual is greater than 17, and wherein, to encode the value of the secondary residual, the one or more processors are not configured to encode a syntax element that specifies the absolute value of the secondary residual minus 17.

26. The device of claim 23 , wherein the first set of CABAC contexts comprises CABAC contexts having context indices between 0 and a−1, and wherein the second set of CABAC contexts comprises CABAC contexts having context indices between a and a+b−1.

27. The device of claim 26 , wherein a is 5, and wherein b is 4.

28. The device of claim 23 , wherein the syntax element comprises a first syntax element, and wherein, to encode the value of the secondary residual further, the one or more processors are configured to:

encode a second syntax element having a value that specifies whether the value of the secondary residual is equal to zero;

where the value of the secondary residual is not equal to zero:

encode a third syntax element having a value that specifies a sign of the value of the secondary residual; and

encode a fourth syntax element having a value that specifies whether the value of the secondary residual is greater than one;

where the value of the secondary residual is greater than one, encode the first syntax element.

29. The device of claim 23 , wherein the current predictive tree node is a first predictive tree node, wherein the syntax element comprises a first syntax element, and wherein the one or more processors are further configured to:

obtain a value of a phi multiplier for geometry coding a second predictive tree node of the point cloud; and

encode the value of the phi multiplier, wherein, to encode the value of the phi multiplier, the one or more processors are configured to:

encode a fifth syntax element having a value that specifies an absolute value of the value of the phi multiplier minus 9.

30. The device of claim 29 , wherein the absolute value of the phi multiplier is greater than 17, and wherein, to encode the value of the phi multiplier, the one or more processors are not configured to encode a syntax element that specifies the value of the phi multiplier minus 17.

31. The device of claim 23 , wherein the current predictive tree node is a first predictive tree node, wherein the syntax element comprises a first syntax element, and wherein the one or more processors are further configured to:

encode, using variable length coding, a sixth syntax element having a value that represents a number of direct child nodes of a second predictive tree node that are present in a geometry predictive tree that represents the point cloud.

32. The device of claim 31 , wherein the sixth syntax element that represents the number of direct child nodes of the second predictive tree node present in the geometry predictive tree comprises a ptn_child_cnt syntax element.

33. The device of claim 31 , wherein, to encode the sixth syntax element using variable length coding, the one or more processors are configured to utilize a shorter codeword where the number of direct child nodes is 1 than where the number of direct child nodes is 0.

34. A device for decoding a point cloud, the device comprising:

a memory configured to store at least a portion of the point cloud; and

one or more processors implemented in circuitry and configured to:

obtain a value of a secondary residual for geometry coding a current predictive tree node of the point cloud; and

decode the value of the secondary residual, wherein, to decode the value, the one or more processors are configured to:

decode, using a first set of context-adaptive binary arithmetic coding (CABAC) contexts, prefix bins of a syntax element, the syntax element having a value that specifies an absolute value of the value of the secondary residual; and

decode, using a second set of CABAC contexts that is different than the first set of contexts, suffix bins of the syntax element.

35. The device of claim 34 , wherein the syntax element comprises a ptn_sec_residual_abs_minus2 syntax element.

36. The device of claim 34 , wherein the absolute value of the secondary residual is greater than 17, and wherein, to decode the value of the secondary residual, the one or more processors are not configured to decode a syntax element that specifies the absolute value of the secondary residual minus 17.

37. The device of claim 34 , wherein the first set of CABAC contexts comprises CABAC contexts having context indices between 0 and a−1, and wherein the second set of CABAC contexts comprises CABAC contexts having context indices between a and a+b−1.

38. The device of claim 37 , wherein a is 5, and wherein b is 4.

39. The device of claim 34 , wherein the syntax element comprises a first syntax element, and wherein, to decode the value of the secondary residual further, the one or more processors are configured to:

decode a second syntax element having a value that specifies whether the value of the secondary residual is equal to zero;

where the value of the secondary residual is not equal to zero:

decode a third syntax element having a value that specifies a sign of the value of the secondary residual; and

decode a fourth syntax element having a value that specifies whether the value of the secondary residual is greater than one;

where the value of the secondary residual is greater than one, decode the first syntax element.

40. The device of claim 34 , wherein the current predictive tree node is a first predictive tree node, wherein the syntax element comprises a first syntax element, and wherein the one or more processors are further configured to:

obtain a value of a phi multiplier for geometry coding a second predictive tree node of the point cloud; and

decode the value of the phi multiplier, wherein, to decode the value of the phi multiplier, the one or more processors are configured to:

decode a fifth syntax element having a value that specifies an absolute value of the value of the phi multiplier minus 9.

41. The device of claim 40 , wherein the absolute value of the phi multiplier is greater than 17, and wherein, to decode the value of the phi multiplier, the one or more processors are not configured to decode a syntax element that specifies the value of the phi multiplier minus 17.

42. The device of claim 34 , wherein the current predictive tree node is a first predictive tree node, wherein the syntax element comprises a first syntax element, and wherein the one or more processors are further configured to:

decode, using variable length coding, a sixth syntax element having a value that represents a number of direct child nodes of a second predictive tree node that are present in a geometry predictive tree that represents the point cloud.

43. The device of claim 42 , wherein the sixth syntax element that represents the number of direct child nodes of the second predictive tree node present in the geometry predictive tree comprises a ptn_child_cnt_syntax element.

44. The device of claim 42 , wherein, to decode the sixth syntax element using variable length coding, the one or more processors are configured to utilize a shorter codeword where the number of direct child nodes is 1 than where the number of direct child nodes is 0.

45. A computer-readable storage medium storing instructions that, when executed, cause one or more processors of a point cloud encoder to:

obtain a value of a secondary residual for geometry coding a current predictive tree node of the point cloud; and

encode the value of the secondary residual, wherein, the instructions that cause the or more processors to encode the value comprise instructions that cause the one or more processors to:

encode, using a first set of context-adaptive binary arithmetic coding (CABAC) contexts, prefix bins of a syntax element, the syntax element having a value that specifies an absolute value of the value of the secondary residual; and

encode, using a second set of CABAC contexts that is different than the first set of contexts, suffix bins of the syntax element.

46. A computer-readable storage medium storing instructions that, when executed, cause one or more processors of a point cloud decoder to:

obtain a value of a secondary residual for geometry coding a current predictive tree node of the point cloud; and

decode the value of the secondary residual, wherein, the instructions that cause the or more processors to decode the value comprise instructions that cause the one or more processors to:

decode, using a first set of context-adaptive binary arithmetic coding (CABAC) contexts, prefix bins of a syntax element, the syntax element having a value that specifies an absolute value of the value of the secondary residual; and

decode, using a second set of CABAC contexts that is different than the first set of contexts, suffix bins of the syntax element.