1. An edge generation method that generates edge information which expresses an area of an edge of an enlarged image resulting from enlarging a unenlarged image on the basis of image data that represents the unenlarged image with gradation data of each pixel, the method comprising: acquiring a position of an edge in correspondence with a position of each pixel of the enlarged image on the basis of the image data; determining a direction of an intended edge according to the gradation data of plural pixels within a predetermined region including the position of the intended edge which determines the direction among the gradation data of each pixel on the enlarged image; correcting the position of the intended edge to a position that brings a direction connecting a position of the intended edge and a position of an edge that is in proximity to the intended edge closer to the determined direction of the intended edge in the enlarged image; and generating the edge information representative of the area of the edge of the enlarged image in correspondence with the position of each pixel of the enlarged image.