Method and apparatus of video coding

1. A video encoding device, comprising:

a processing circuit configured to:

receive a first block, a second block, and a third block of an image frame, wherein the first block corresponds to a first color space component of a color space, the second block corresponds to a second color space component of the color space, and the third block corresponds to a third color space component of the color space;

apply a first transform process to a first residual portion of the first block, a second residual portion of the second block, and a third residual portion of the third block to generate a first transformed block, a second transformed block, and a third transformed block, respectively;

when a second transform process is to be applied to the first transformed block and the second transformed block,

generate a first syntax element set to be signaled in association with the first color space component, the first syntax element set indicating a first transform setting for applying the second transform process to the first transformed block,

generate a second syntax element set to be signaled in association with the second color space component, the second syntax element set indicating a second transform setting for applying the second transform process to the second transformed block, and

generate encoded video data for output to include the first syntax element set and the second syntax element set;

determine whether a third transform setting for applying the second transform process to the third transformed block is to be signaled in association with the third color space component or the second color space component;

when the third transform setting is determined to be signaled in association with the third color space component, determine the third transform setting and generate a third syntax element set to be signaled in association with the third color space component; and

when the third transform setting is determined to be signaled in association with the second color space component, use the second transform setting as the third transform setting, without generating the third syntax element set.

2. The video encoding device according to claim 1 , wherein

the determined first transform setting includes information indicating first candidate transform matrices, or a selected first transform matrix, for the second transform process to be applied to the first transformed block, and

the determined second transform setting includes information indicating second candidate transform matrices, or a selected second transform matrix, for the second transform process to be applied to the second transformed block.

3. The video encoding device according to claim 1 , wherein the processing circuit is further configured to include a flag in the encoded video data, the flag indicating whether the third transform setting is to be signaled in association with the third color space component or the second color space component.

4. The video encoding device according to claim 3 , wherein the processing circuit is further configured to include the flag using a video level, picture level, slice level, tile level, or sequence level syntax element.

5. The video encoding device according to claim 1 , wherein the processing circuit is further configured to determine whether the third transform setting is to be signaled in association with the third color space component or the second color space component based on block partitioning structures corresponding to the second color space component and the third color space component.

6. The video encoding device according to claim 5 , wherein the processing circuit is further configured to:

determine that the third transform setting is to be signaled in association with the second color space component when the block partitioning structures corresponding to the second color space component and the third color space component are the same; and

determine that the third transform setting is to be signaled in association with the third color space component when the block partitioning structures corresponding to the second color space component and the third color space component are the different.

7. The video encoding device according to claim 1 , wherein the first color space component corresponds to a luma component, and the second color space component corresponds to a chroma component.

8. The video encoding device according to claim 1 , wherein the second color space component corresponds to a first chroma component, and the third color space component corresponds to a second chroma component.

9. A video encoding method, comprising:

receiving a first block, a second block, and a third block of an image frame, wherein the first block corresponds to a first color space component of a color space, the second block corresponds to a second color space component of the color space, and the third block corresponds to a third color space component of the color space;

applying a first transform process to a first residual portion of the first block, a second residual portion of the second block, and a third residual portion of the third block to generate a first transformed block, a second transformed block, and a third transformed block, respectively;

when a second transform process is to be applied to the first transformed block and the second transformed block,

generating a first syntax element set to be signaled in association with the first color space component, the first syntax element set indicating a first transform setting for applying the second transform process to the first transformed block,

generating a second syntax element set to be signaled in association with the second color space component, the second syntax element set indicating a second transform setting for applying the second transform process to the second transformed block, and

generating encoded video data for output to include the first syntax element set and the second syntax element set;

determining whether a third transform setting for applying the second transform process to the third transformed block is to be signaled in association with the third color space component or the second color space component;

when the third transform setting is determined to be signaled in association with the third color space component, determining the third transform setting and generating a third syntax element set to be signaled in association with the third color space component; and

when the third transform setting is determined to be signaled in association with the second color space component, using the second transform setting as the third transform setting, without generating the third syntax element set.

10. A video decoding device, comprising:

a processing circuit configured to:

receive encoded video data associated with a first block, a second block, and a third block of an image frame, wherein the first block corresponds to a first color space component of a color space, the second block corresponds to a second color space component of the color space, and the third block corresponds to a third color space component of the color space;

obtain a first transformed block of a first residual portion of the first block and a second transformed block of a second residual portion of the second block from the encoded video data, including

when a first inverse transform process is to be applied to a first encoded residual portion of the first block and a second encoded residual portion of the second block,

identifying a first transform setting for applying the first inverse transform process to the first encoded residual portion of the first block based on a first syntax element set signaled in association with the first color space component,

identifying a second transform setting for applying the first inverse transform process to the second encoded residual portion of the second block based on a second syntax element set signaled in association with the second color space component,

applying the first inverse transform process to the first encoded residual portion to generate the first transformed block based on the identified first transform setting, and

applying the first inverse transform process to the second encoded residual portion to generate the second transformed block based on the identified second transform setting;

apply a second inverse transform process to the first transformed block and the second transformed block to generate the first residual portion and the second residual portion for output, respectively;

determine whether a third transform setting for applying the first inverse transform process to a third encoded residual portion of the third block is to be signaled in association with the third color space component or the second color space component;

when the third transform setting is determined to be signaled in association with the third color space component, identify the third transform setting based on a third syntax element set signaled in association with the third color space component; and

when the third transform setting is determined to be signaled in association with the second color space component, use the second transform setting as the third transform setting, without identifying the third transform setting based on the third syntax element set.

11. The video decoding device according to claim 10 , wherein

the identified first transform setting includes information indicating first candidate transform matrices, or a selected first transform matrix, for the first inverse transform process used to generate the first transformed block, and

the identified second transform setting includes information indicating second candidate transform matrices, or a selected second transform matrix, for the first inverse transform process used to generate the second transformed block.

12. The video decoding device according to claim 10 , wherein the processing circuit is further configured to extract a flag from the encoded video data, the flag indicating whether the third transform setting is to be signaled in association with the third color space component or the second color space component.

13. The video decoding device according to claim 12 , wherein the processing circuit is further configured to extract the flag from video level, picture level, slice level, tile level, or sequence level syntax elements.

14. The video decoding device according to claim 10 , wherein the processing circuit is further configured to derive whether the third transform setting is to be signaled in association with the third color space component or the second color space component.

15. The video decoding device according to claim 14 , wherein the processing circuit is further configured to:

determine that the third transform setting is to be signaled in association with the second color space component when block partitioning structures corresponding to the second color space component and the third color space component are the same; and

determine that the third transform setting is to be signaled in association with the third color space component when the block partitioning structures corresponding to the second color space component and the third color space component are the different.

16. The video decoding device according to claim 10 , wherein the first color space component corresponds to a luma component, and the second color space component corresponds to a chroma component.

17. The video decoding device according to claim 10 , wherein the second color space component corresponds to a first chroma component, and the third color space component corresponds to a second chroma component.

18. A video decoding method, comprising:

receiving encoded video data associated with a first block, a second block, and a third block of an image frame, wherein the first block corresponds to a first color space component of a color space, the second block corresponds to a second color space component of the color space, and the third block corresponds to a third color space component of the color space;

obtaining a first transformed block of a first residual portion of the first block and a second transformed block of a second residual portion of the second block from the encoded video data, including

when a first inverse transform process is to be applied to a first encoded residual portion of the first block and a second encoded residual portion of the second block,

identifying a first transform setting for applying the first inverse transform process to the first encoded residual portion of the first block based on a first syntax element set signaled in association with the first color space component,

identifying a second transform setting for applying the first inverse transform process to the second encoded residual portion of the second block based on a second syntax element set signaled in association with the second color space component;

applying the first inverse transform process to the first encoded residual portion to generate the first transformed block based on the identified first transform setting, and

applying the first inverse transform process to the second encoded residual portion to generate the second transformed block based on the identified second transform setting;

applying a second inverse transform process to the first transformed block and the second transformed block to generate the first residual portion and the second residual portion, respectively;

determining whether a third transform setting for applying the first inverse transform process to a third encoded residual portion of the third block is to be signaled in association with the third color space component or the second color space component;

when the third transform setting is determined to be signaled in association with the third color space component, identifying the third transform setting based on a third syntax element set signaled in association with the third color space component; and

when the third transform setting is determined to be signaled in association with the second color space component, using the second transform setting as the third transform setting, without identifying the third transform setting based on the third syntax element set.