A video decoding method comprises when a first offset method is applied to a current slice comprising a current block, adjusting an offset with respect to the current block, based on a first offset parameter of the current block; when the first offset method is applied to the current slice, determining whether to apply a second offset method to the current slice; when the second offset method is applied to the current slice, determining a second offset parameter of the current block; and applying an offset based on the second offset parameter to the current block to which the offset based on the first offset parameter is applied, wherein the first offset parameter and the second offset parameter comprise offset values for the current block.