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 an area of a specific layer; correcting difference between a pixel statistical value of the specific layer and the pixel statistical value of a layer that is wider than the specific layer using the post-correction edge; correcting the pixel statistical value of the specific layer using post-correction difference and the pixel statistical value of the layer that is wider than the specific layer; and correcting the target pixel by repeating correction of the pixel statistical value successively in each layer until the area reduces its range from the maximum range to the minimum range.