Transform in intra prediction-based image coding
An image decoding method according to the present document comprises the steps of: acquiring prediction-related information and residual-related information for a current block; deriving transform coefficients for the current block on the basis of the residual-related information; and generating residual samples of the current block on the basis of the transform coefficients, wherein the residual-related information includes low-frequency non-separable transform (LFNST) index information indicating information relating to non-separable transform for a low-frequency transform coefficient of the current block on the basis of a matrix-based intra prediction (MIP) flag.
1 . An apparatus comprising:
a memory; and
at least one processor connected to the memory, wherein the at least one processor is configured to:
obtain prediction related information and information on transform coefficients for a current block from a bitstream;
derive transform coefficients for the current block based on the information on the transform coefficients;
derive modified transform coefficients from the transform coefficients based on a transform kernel in a low frequency non-separable transform (LFNST) transform set for the current block;
generate residual samples of the current block based on the modified transform coefficients; and
generate reconstructed samples of the current block based on the residual samples,
wherein the information on the transform coefficients includes LFNST index information related to the transform kernel for the current block,
wherein the prediction related information includes a matrix based intra prediction (MIP) flag which is always parsed prior to the LFNST index information,
wherein an enabled flag is included in a sequence parameter set (SPS) and the SPS is included in the bitstream,
wherein based on the enabled flag representing that an LFNST is enabled and the MIP flag representing that an MIP is not applied, the LFNST index information is present, and
wherein based on the MIP flag representing that the MIP is applied, the LFNST index information is not present and a value of the LFNST index information is derived as 0.
2 . An apparatus comprising:
a memory; and
at least one processor connected to the memory, wherein the at least one processor is configured to:
determine an intra prediction mode and an intra prediction type for a current block;
generate prediction related information for the current block based on the intra prediction mode and the intra prediction type;
derive prediction samples of the current block based on the intra prediction mode and the intra prediction type;
generate residual samples of the current block based on the prediction samples;
derive temporary transform coefficients for the current block based on the residual samples;
derive transform coefficients for the current block from the temporary transform coefficients based on a transform kernel;
generate information on the transform coefficients; and
encode the prediction related information and the information on the transform coefficients to output a bitstream,
wherein the information on the transform coefficients includes low frequency non-separable transform (LFNST) index information related to the transform kernel in an LFNST transform set for the current block,
wherein the prediction related information includes a matrix based intra prediction (MIP) flag which is always encoded prior to the LFNST index information,
wherein an enabled flag is included in a sequence parameter set (SPS) and the SPS is included in the bitstream,
wherein based on the enabled flag representing that the LFNST is enabled and the MIP flag representing that the MIP is not applied, the LFNST index information is present, and
wherein based on the MIP flag representing that the MIP is applied, the LFNST index information is not present and a value of the LFNST index information is equal to 0.
3 . An apparatus comprising:
at least one processor configured to obtain a bitstream for the image, the bitstream is generated based on determining an intra prediction mode and an intra prediction type for a current block, generating prediction related information for the current block based on the intra prediction mode and the intra prediction type, deriving prediction samples of the current block based on the intra prediction mode and the intra prediction type, generating residual samples of the current block based on the prediction samples, deriving temporary transform coefficients for the current block based on the residual samples, deriving transform coefficients for the current block from the temporary transform coefficients based on a transform kernel, generating information on the transform coefficients, and encoding the prediction related information and the information on the transform coefficients; and
a transmitter configured to transmit data comprising the bitstream,
wherein the information on the transform coefficients includes low frequency non-separable transform (LFNST) index information related to the transform kernel in an LFNST transform set for the current block,
wherein the prediction related information includes a matrix based intra prediction (MIP) flag which is always encoded prior to the LFNST index information,
wherein an enabled flag is included in a sequence parameter set (SPS) and the SPS is included in the bitstream,
wherein based on the enabled flag representing that the LFNST is enabled and the MIP flag representing that the MIP is not applied, the LFNST index information is present, and
wherein based on the MIP flag representing that the MIP is applied, the LFNST index information is not present and a value of the LFNST index information is equal to 0.