An image decoding method performed by a decoding apparatus, according to the present document, comprises the steps of: acquiring image information including chroma quantization parameter data of at least one chroma QP mapping table for chroma components, and prediction information and residual information regarding the chroma components; deriving the chroma QP mapping table on the basis of the chroma quantization parameter data; deriving a chroma quantization parameter for the chroma components on the basis of the chroma QP mapping table; deriving prediction samples for the chroma components on the basis of the prediction information; deriving residual samples on the basis of the residual information and the chroma quantization parameter; and generating a reconstructed picture on the basis of the prediction samples and the residual samples.