1. An image processing device, comprising: a color information obtaining part obtaining at least hue from color information of each pixel of a color image; a detecting part detecting a mode value of the hue on a color space; a range setting part setting a predetermined range on the color space including the mode value of the hue detected by the detecting part as a target range; a changing part changing hue of a pixel included in the target range by virtually performing extension on the target range; and an information converting part converting color information of a pixel having hue not included in the target range into color information indicative of an achromatic color.