1. A method of reducing a blocking artifact appearing when coding a picture, comprising: dividing the picture into blocks that each include multiple pixels, wherein the pixels of a first block are separated from pixels of a neighboring second block by a block boundary; selecting a correction mode using information from the first block and information from the second block, wherein the correction mode is selected from at least two correction modes; selecting a quantity of pixels to be adjusted based on the selected correction mode; and adjusting the selected quantity of pixels.