According to the present invention, an image decoding method performed by a decoding device comprises the steps of: deriving a prediction mode of a current block; generating a prediction block of the current block on the basis of the prediction mode of the current block; deriving a neighboring block of the current block; deriving correlation information on the basis of a reconstruction block of the neighboring block and a prediction block of the neighboring block; deriving a modified prediction block of the current block on the basis of the prediction block of the current block and the correlation information; and deriving a reconstruction block of the current block on the basis of the modified prediction block. According to the present invention, a current block can be predicted in consideration of the correlation between a prediction sample and a reconstruction sample of a neighboring block, and a complicated image can be more efficiently reconstructed through the prediction.