An edge pixel is extracted from an input image by an edge determination section, an object image section is extracted by an object-image extraction section, and a first characteristic amount of the object image section in a first local pixel block containing a first target pixel is calculated by a first-characteristic-amount calculation section. A classification is made as to whether the first target pixel is a character edge pixel or a dot edge pixel by an edge-class determination section on the basis of the result of extraction for the edge pixel and the first characteristic amount. A second characteristic amount of a second local pixel block containing a second target pixel is calculated by a second-characteristic-amount calculation section on the basis of the edge classification result. The image of the second target pixel is classified by an image-class determination section on the basis of the second characteristic amount.