An image decoding method is disclosed. The image decoding method includes determining a prediction mode of a current block based on prediction mode information of the current block obtained from a bitstream, obtaining a transform coefficient block of the current block from the bitstream, dequantizing the transform coefficient to generate a dequantized transform coefficient block, determining a transform kernel for the dequantized transform coefficient block, and generating a residual block of the current block by performing inverse transform on the dequantized transform coefficient block using the transform kernel.