A picture filtering method performed by an encoding apparatus, the method comprising steps of: defining regions for adaptive loop filtering, ALF, from a current picture by using a RD cost, wherein each of the regions for the ALF includes a plurality of coding units, CUs; determining ALF coefficients in a picture unit or a region unit; determining whether the ALF is available in the region unit by using the ALF coefficients; redetermining ALF coefficients with respect to a first region for which the ALF is available; deriving a filter shape for the first region; determining whether the ALF is available for the current picture by using the redetermined ALF coefficients; determining whether the ALF is available in the CU within the first region by using the redetermined ALF coefficients; performing filtering on an ALF-available CU by using the derived filter shape and the redetermined ALF coefficients; and transmitting a region-based ALF enabled flag, region-level ALF available flag information, information on a filter shape and ALF coefficients on the region for which the ALF is available, CU-level ALF-available flag information, and information on the regions for the ALF in the current picture, wherein the information on the regions for the ALF is transmitted when a value of the region-based ALF enabled flag is equal to 1, wherein the information on the regions for the ALF includes number information of region columns in the current picture, number information of region rows in the current picture, and uniform region flag information representing whether the regions for the ALF in the current picture has uniform columns and uniform rows, wherein when a value of the uniform region flag is equal to 0, the information on the regions for the ALF further includes width information of each region and height information of each region. defining regions for adaptive loop filtering, ALF, from a current picture by using a RD cost, wherein each of the regions for the ALF includes a plurality of coding units, CUs; determining ALF coefficients in a picture unit or a region unit; determining whether the ALF is available in the region unit by using the ALF coefficients; redetermining ALF coefficients with respect to a first region for which the ALF is available; deriving a filter shape for the first region; determining whether the ALF is available for the current picture by using the redetermined ALF coefficients; determining whether the ALF is available in the CU within the first region by using the redetermined ALF coefficients; performing filtering on an ALF-available CU by using the derived filter shape and the redetermined ALF coefficients; and transmitting a region-based ALF enabled flag, region-level ALF available flag information, information on a filter shape and ALF coefficients on the region for which the ALF is available, CU-level ALF-available flag information, and information on the regions for the ALF in the current picture, wherein the information on the regions for the ALF is transmitted when a value of the region-based ALF enabled flag is equal to 1, wherein the information on the regions for the ALF includes number information of region columns in the current picture, number information of region rows in the current picture, and uniform region flag information representing whether the regions for the ALF in the current picture has uniform columns and uniform rows,