Transform-based image coding method, and apparatus therefor

An image encoding method performed by an encoding apparatus, the method comprising:

• deriving prediction samples for a current block;
• deriving residual samples for the current block based on the prediction samples;
• performing a transform coefficient derivation operation of deriving transform coefficients for the current block by applying at least one of a Low Frequency Non-Separable Transform (LFNST) or a Multiple Transform Selection (MTS) to the residual samples and arranging the transform coefficients according to a predetermined scan order;
• encoding at least one of an LFNST index related to an LFNST kernel or an MTS index related to an MTS kernel;
• and
• constructing and outputting image information so that the LFNST index and the MTS index are signaled in a coding unit level and the MTS index is signaled immediately after the LFNST index is signaled,
• wherein, in response to a case where a tree type of the current block is a single-tree type, the LFNST index is encoded after the transform coefficient derivation operation for a luma block and a chroma block of the current block is performed, and
• wherein, in response to a case where a tree type of the current block is a dual-tree chroma type, the LFNST index is encoded after the transform coefficient derivation operation for a Cb component and a Cr component of the chroma block is performed.

A method for transmitting data for image information comprising:

• generating a bitstream of the image information, wherein the bitstream is generated based on deriving prediction samples for a current block;
• deriving residual samples for the current block based on the prediction samples;
• performing a transform coefficient derivation operation of deriving transform coefficients for the current block by applying at least one of a Low Frequency Non-Separable Transform (LFNST) or a Multiple Transform Selection (MTS) to the residual samples and arranging the transform coefficients according to a predetermined scan order;
• encoding at least one of an LFNST index related to an LFNST kernel or an MTS index related to an MTS kernel;
• and constructing and outputting the image information so that the LFNST index and the MTS index are signaled in a coding unit level and the MTS index is signaled immediately after the LFNST index is signaled;
• and
• transmitting the data comprising the bitstream,
• wherein, in response to a case where a tree type of the current block is a single-tree type, the LFNST index is encoded after the transform coefficient derivation operation for a luma block and a chroma block of the current block is performed, and
• wherein, in response to a case where a tree type of the current block is a dual-tree chroma type, the LFNST index is encoded after the transform coefficient derivation operation for a Cb component and a Cr component of the chroma block is performed.