Method and apparatus of video coding

A video decoding method, comprising:

• receiving encoded video data associated with a current block of a current frame, wherein the current block corresponds to a first color space component of a color space, a second color space component of the color space, and a third color space component of the color space;
• deriving quantized data of the current block based on the encoded video data;
• performing an inverse quantization process on the quantized data to derive transformed data of the current block;
• deriving a first transform setting of an inverse secondary transform process for the transformed data associated with the first color space component from the encoded video data;
• deriving a second transform setting of the inverse secondary transform process for the transformed data associated with the second color space component and the third color component from the encoded video data;
• deriving an intermediate transformed data of the current block by:
• performing the inverse secondary transform process to the transformed data associated with the first color space component based on the first transform setting;
• and
• performing the inverse secondary transform process to the transformed data associated with the second color space component and the third color space component based on the second transform setting;
• performing an inverse core transform process on the intermediate transformed data associated with at least one of the first color space component, the second color space component, and the third color space component to generated residual data of the current block;
• decoding the current block based on the residual data and prediction data generated by a prediction process of the current block.

A video decoding device, comprising:

• a processing circuit configured to:
• receive encoded video data associated with a current block of a current frame, wherein the current block corresponds to a first color space component of a color space, a second color space component of the color space, and a third color space component of the color space;
• derive quantized data of the current block based on the encoded video data;
• perform an inverse quantization process on the quantized data to derive transformed data of the current block;
• derive a first transform setting of an inverse secondary transform process for the transformed data associated with the first color space component from the encoded video data;
• derive a second transform setting of the inverse secondary transform process for the transformed data associated with the second color space component and the third color component from the encoded video data;
• derive an intermediate transformed data of the current block by:
• performing the inverse secondary transform process to the transformed data associated with the first color space component based on the first transform setting;
• and
• performing the inverse secondary transform process to the transformed data associated with the second color space component and the third color space component based on the second transform setting;
• perform an inverse core transform process on the intermediate transformed data associated with at least one of the first color space component, the second color space component, and the third color space component to generated residual data of the current block;
• decode the current block based on the residual data and prediction data generated by a prediction process of the current block.