According to the disclosure of the present document, an image decoding method performed by a decoding device comprises the steps: acquiring, through a
bitstream, image information including prediction mode information and residual information; deriving a prediction mode of a current block on the basis of the prediction mode information; deriving prediction samples on the basis of the prediction mode; deriving residual samples on the basis of the residual information; generating reconstruction samples on the basis of the prediction samples and the residual samples; deriving filter coefficients for an adaptive
loop filter (ALF) procedure for the reconstruction samples; and generating modified reconstruction samples on the basis of the reconstruction samples and the filter coefficients, wherein the image information includes a first
adaptation parameter set (APS) including an ALF
data field, and the ALF
data field includes ALF parameters used to derive the filter coefficients.