Methods and apparatuses of signaling quantization parameter in video processing system

1. A method of processing video data in a video decoding system, wherein video data is partitioned into leaf Coding Units (CUs) according to a CU partitioning structure, the method comprising:

receiving input data associated with a current split node, wherein the current split node is partitioned from a parent node by a splitting type;

determining a depth of the current split node according to the splitting type;

determining a value of a variable by comparing the depth of the current split node with a maximum delta Quantization Parameter (QP) signaling depth;

deriving a delta QP from one or more syntax elements signaled or parsed in a Transform Unit (TU) associated with the current split node according to the value of the variable;

reconstructing a final QP for one or more TUs associated with the current split node based on a reference QP and the delta QP when the one or more syntax elements are signaled or parsed for the current split node; and

decoding the one or more TUs associated with the current split node using the final QP.

2. The method of claim 1 , wherein the maximum delta QP signaling depth is predefined, derived, parsed or signaled in one or a combination of a slice, picture, tile, and sequence level.

3. The method of claim 1 , wherein the depth of the current split node is determined by an area of the current split node and the maximum delta QP signaling depth is derived by a minimum delta QP signaling CU area.

4. The method of claim 3 , wherein the area of the current split node is determined from a block width and a block height of the current split node, and the minimum delta QP signaling CU area is predefined, derived, parsed or signaled in one or a combination of a slice, picture, tile, and sequence level.

5. The method of claim 3 , wherein the current split node is a leaf CU, and the delta QP is derived from the one or more syntax elements when the area of the current split node is larger than or equal to the minimum delta QP signaling CU area and there is at least one non-zero coefficient or at least one escape palette in the current split node.

6. The method of claim 3 , wherein the current split node is not a leaf CU and is further partitioned into multiple leaf CUs, the delta QP is derived from the one or more syntax elements when the current split node has a size larger than or equal to the minimum delta QP signaling CU area, an area of at least one children node partitioned from the current split node is smaller than the minimum delta QP signaling CU area, and at least one of the leaf CUs in the current split node has at least one non-zero coefficient or at least one escape palette, wherein the delta QP is used by one or more of the leaf CUs within the current split node.

7. The method of claim 1 , wherein the current split node is a leaf CU, the delta QP is derived from the one or more syntax elements when the depth of the current split node is smaller than or equal to the maximum delta QP signaling depth and the current split node has at least one non-zero coefficient or at least one escape palette.

8. The method of claim 1 , wherein when the current split node is not a leaf CU and is further partitioned into multiple leaf CUs, the delta QP is derived from the one or more syntax elements when the depth of the current split node is smaller than or equal to the maximum delta QP signaling depth, a depth of at least one children node partitioned from the current split node is larger than the maximum delta QP signaling depth, and at least one of the leaf CUs in the current split node has at least one non-zero coefficient or at least one escape palette, wherein the delta QP is used by one or more of the leaf CUs within the current split node.

9. The method of claim 1 , wherein the maximum delta QP signaling depth is signaled or parsed separately for luma and chroma components when separate CU partitioning structures are employed for partitioning the video data of the luma and chroma components.

10. The method of claim 1 , wherein the depth of the current split node is a depth of the parent node plus 2 when the current split node is a first or third split node of Ternary Tree (TT) splitting, the depth of the current split node is a depth of the parent node plus 1 when the current split node is a second split node of TT splitting, the depth of the current split node is a depth of the parent node plus 1 when the current split node is partitioned from the parent node by Binary Tree (BT) splitting, and the depth of the current split node is a depth of the parent node plus 2 when the current split node is partitioned from the parent node by quadtree splitting.

11. The method of claim 1 , wherein the current split node is further partitioned into multiple children nodes, wherein a depth of a children node is the depth of the current split node plus 2 when the children node is a first or third split node of Ternary Tree (TT) splitting, a depth of a children node is the depth of the current split node plus 1 when the child node is a second split node of TT splitting, a depth of a children node is the depth of the current split node plus 1 when the children node is partitioned from the current split node by Binary Tree (BT) splitting, and a depth of a children node is the depth of the current split node plus 2 when the children node is partitioned from the current split node by quadtree splitting.

12. The method of claim 1 , wherein when the current split node is a first or third split node partitioned from the parent node by Ternary Tree (TT) splitting, the depth of the current split node is larger than the maximum delta QP signaling depth, a depth of a second split node partitioned from the parent node is equal to the maximum delta QP signaling depth, and the delta QP derived from the one or more syntax elements is used by one or more of the three split nodes partitioned from the parent node.

13. The method of claim 1 , wherein a flag indicating whether the current split node is a first or third split node in Ternary Tree (TT) splitting, a flag indicating whether the current split node is a second split node in TT splitting, a parent CU size, or a combination thereof is also used to determine the value of the variable for the current split node.

14. The method of claim 1 , wherein one or more delta QP related information is passed from the parent node to the current split node to determine the value of the variable for the current split node.

15. The method of claim 14 , wherein the one or more delta QP related information includes a reset flag for the current split node, and the reset flag is determined by referring to the area, size, or depth of the current split node or the splitting type for partitioning the parent node.

16. The method of claim 1 , wherein one or more delta QP related information is passed from the current split node to one or more children nodes partitioned from the current split node to determine the value of the variable for the one or more children nodes.

17. The method of claim 16 , wherein the one or more delta QP related information includes a reset flag for the one or more children nodes, and the reset flag is determined by referring to an area, size, or depth of the one or more children nodes and a splitting type for partitioning the current split node.

18. The method of claim 17 , wherein the reset flag is determined by comparing the depth of the current node plus a second variable with the maximum delta QP signaling depth, wherein the second variable is equal to 2 when the current split node is partitioned by Ternary Tree (TT) splitting or by quadtree splitting, the second variable is equal to 1 when the current split node is partitioned by Binary Tree (BT).

19. The method of claim 1 , wherein at most one delta QP is derived for all children nodes partitioned from the current split node by Ternary Tree (TT) splitting when the depth of the current split node is smaller than or equal to the maximum delta QP signaling depth and a depth of at least one children node partitioned from the current split node is larger than the maximum delta QP signaling depth, and the delta QP derived from the one or more syntax elements is used by one or more of the children nodes partitioned from the current split node.

20. The method of claim 1 , wherein the reference QP is a slice QP when the CU partitioning structure is a Quad-Tree-Binary-Tree (QTBT) or Multi-Type-Tree (MTT) partitioning structure.

21. An apparatus of processing video data in a video decoding system, wherein video data is partitioned into leaf Coding Units (CUs) according to one or more CU partitioning structures, the apparatus comprising one or more electronic circuits configured for:

receiving input data associated with a current split node, wherein the current split node is partitioned from a parent node by a splitting type;

determining a depth of the current split node according to the splitting type;

determining a value of a variable by comparing the depth of the current split node with a maximum delta Quantization Parameter (QP) signaling depth;

deriving a delta QP from one or more syntax elements signaled or parsed in a Transform Unit (TU) associated with the current split node according to the value of the variable;

reconstructing a final QP for one or more TUs associated with the current split node based on a reference QP and the delta QP when the one or more syntax elements are signaled or parsed for the current split node; and

decoding the one or more TUs associated with the current split node using the final QP.

22. A non-transitory computer readable medium storing program instructions causing a processing circuit of an apparatus to perform a video processing method, and the method comprising:

receiving input data associated with a current split node, wherein the current split node is partitioned from a parent node by a splitting type;

determining a depth of the current split node according to the splitting type;

determining a value of a variable by comparing the depth of the current split node with a maximum delta Quantization Parameter (QP) signaling depth;

deriving a delta QP from one or more syntax elements signaled or parsed in a Transform Unit (TU) associated with the current split node according to the value of the variable;

reconstructing a final QP for one or more TUs associated with the current split node based on a reference QP and the delta QP when the one or more syntax elements are signaled or parsed for the current split node; and

decoding the one or more TUs associated with the current split node using the final QP.

23. A method of processing video data in a video encoding system, wherein video data is partitioned into leaf Coding Units (CUs) according to a CU partitioning structure, the method comprising:

receiving input data associated with a current split node, wherein the current split node is partitioned from a parent node by a splitting type;

determining a depth of the current split node according to the splitting type;

determining a Quantization Parameter (QP) for the current split node according to a comparing result of the depth of the current split node and a maximum delta QP signaling depth;

deriving a delta QP from the QP for the current split node and a reference QP and signaling one or more syntax elements of the delta QP in a Transform Unit (TU) associated with the current split node; and

encoding one or more TUs of the current split node using the QP.

24. An apparatus of processing video data in a video encoding system, wherein video data is partitioned into leaf Coding Units (CUs) according to one or more CU partitioning structures, the apparatus comprising one or more electronic circuits configured for:

receiving input data associated with a current split node, wherein the current split node is partitioned from a parent node by a splitting type;

determining a depth of the current split node according to the splitting type;

determining a Quantization Parameter (QP) for the current split node according to a comparing result of the depth of the current split node and a maximum delta QP signaling depth;

deriving a delta QP according to the QP for the current split node and a reference QP and signaling one or more syntax elements of the delta QP in a Transform Unit (TU) associated with the current split node; and

encoding one or more TUs of the current split node according to the QP.

25. A non-transitory computer readable medium storing program instruction instructions causing a processing circuit of an apparatus to perform a video processing method, the method comprising:

receiving input data associated with a current split node, wherein the current split node is partitioned from a parent node by a splitting type;

determining a depth of the current split node according to the splitting type;

determining a Quantization Parameter (QP) for the current split node according to a comparing result of the depth of the current split node and a maximum delta QP signaling depth;

deriving a delta QP according to the QP for the current split node and a reference QP and signaling one or more syntax elements of the delta QP in a Transform Unit (TU) associated with the current split node; and

encoding one or more TUs of the current split node according to the QP.