A method includes: calculating a pixel statistical value and edge of pixels for each of areas of a multi-layer, the areas each containing a target pixel and having a successively decreased range; correcting the edge based on a pixel statistical value of an area that is wider than a specific area; correcting difference between a pixel statistical value of the specific area and the pixel statistical value of the area that is wider than the specific area using the post-correction edge; correcting the pixel statistical value of the specific area using post-correction difference and the pixel statistical value of the area that is wider than the specific area; and correcting the target pixel by repeating correction of the pixel statistical value of the specific area successively in each area until the area reduces its range from the maximum range to the minimum range.