Non-separable primary transform design method and apparatus

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

• deriving residual samples for a current block;
• deriving transform coefficients for the current block by performing a primary transform on the residual samples based on a transform kernel;
• generating transform index information related to the transform kernel among a plurality of transform kernels;
• generating residual information based on the transform coefficients;
• and
• encoding image information including the transform index information and the residual information,
• wherein the plurality of transform kernels include a separable transform kernel and a non-separable transform kernel, and
• wherein the image information further includes a flag indicating whether the non-separable transform kernel is applied to the primary transform.

A transmission method of data for image, the method comprising:

• obtaining a bitstream for the image, wherein the bitstream is generated based on deriving residual samples for a current block, deriving transform coefficients for the current block by performing a primary transform on the residual samples based on a transform kernel, generating transform index information related to the transform kernel among a plurality of transform kernels, generating residual information based on the transform coefficients, and encoding image information including the transform index information and the residual information;
• and
• transmitting the data comprising the bitstream,
• wherein the plurality of transform kernels include a separable transform kernel and a non-separable transform kernel, and
• wherein the image information further includes a flag indicating whether the non-separable transform kernel is applied to the primary transform.