Image encoding/decoding method and apparatus, and recording medium having bitstream stored thereon

An image encoding method, comprising:

• deriving residual samples of a current block;
• determining a non-separable primary transform (NSPT) set for the current block;
• applying a NSPT to the residual samples of the current block based on any one of a plurality of NSPT kernel candidates belonging to the NSPT set to derive transform coefficients of the current block;
• and
• encoding a transform index specifying the any one of the plurality of NSPT kernel candidates and the transform coefficients of the current block to generate a bitstream,
• wherein the NSPT is applied based on a size of the current block belonging to a group of one or more block sizes to which the NSPT is applicable.

A method for transmitting data, comprising:

• obtaining a bitstream for image information, wherein the bitstream is generated by deriving residual samples of a current block, determining a non-separable primary transform (NSPT) set for the current block, applying an NSPT to the residual samples of the current block based on any one of a plurality of NSPT kernel candidates belonging to the NSPT set to derive transform coefficients of the current block, and encoding a transform index specifying the any one of the plurality of NSPT kernel candidates and the transform coefficients of the current block;
• and
• transmitting the data including the bitstream,
• wherein the NSPT is applied based on a size of the current block belonging to a group of one or more block sizes to which the NSPT is applicable.