Primary transforms for cross-component level reconstruction

A device for video processing, the device comprising a memory for storing computer instructions and a processor in communication with the memory, wherein, when the processor executes the computer instructions, the processor is configured to cause the device to:

• receive a bitstream of a video block comprising a first transform block of a first color component and a second transform block of a second color component, wherein the first transform block and the second transform blocks are co-located blocks;
• obtain the first transform block of the first color component and the second transform block of the second color component from the bitstream of the video block;
• determine a first flag indicating that all transform coefficients in the first transform block are zero;
• determine a second flag indicating that a cross component level reconstruction (CCLR) is applied to the first transform block;
• and
• in response to determining that CCLR is applied to the first transform block:
• refine one or more of the transform coefficients in the first transform block by adding one or more offset values, to obtain a refined first transform block, the one or more offset values being derived based on transform coefficients that are in the second transform block and are co-located with the one or more of the transform coefficients in the first transform block;
• determine a target transform kernel for the refined first transform block;
• perform a reverse transform on the refined first transform block based on the target transform kernel to obtain a target block;
• and
• reconstruct the first color component of the video block based on at least the target block.

A non-transitory storage medium for storing computer readable instructions, the computer readable instructions, when executed by a processor of device for processing video data, causing the processor to:

• receive a bitstream of a video block comprising a first transform block of a first color component and a second transform block of a second color component, wherein the first transform block and the second transform blocks are co-located blocks;
• obtain the first transform block of the first color component and the second transform block of the second color component from the bitstream of the video block;
• determine a first flag indicating that all transform coefficients in the first transform block are zero;
• determine a second flag indicating that a cross component level reconstruction (CCLR) is applied to the first transform block;
• and
• in response to determining that CCLR is applied to the first transform block:
• refine one or more of the transform coefficients in the first transform block by adding one or more offset values, to obtain a refined first transform block, the one or more offset values being derived based on transform coefficients that are in the second transform block and are co-located with the one or more of the transform coefficients in the first transform block;
• determine a target transform kernel for the refined first transform block;
• perform a reverse transform on the refined first transform block based on the target transform kernel to obtain a target block;
• and
• reconstruct the first color component of the video block based on at least the target block.