A texture processing unit obtains smoothness information from a paper type specifying unit or a smoothness measuring device, and a lookup table is selected corresponding to the smoothness. An image area division unit divides off image signals of a predetermined hue area from among converted image signals. Predetermined hue area refers to a hue area in which, among multiple areas of different hues, a toner transfer failure tends to occur at concave portions that exist on a printing surface of a printing medium. The image signal processing unit applies the lookup table selected by the texture processing unit on the image signals that have been divided off, thereby increasing the toner amounts at concave portions.