A color separating unit separates a color image into plural color components to generate images of respective colors. A periodicity determining unit determines, for each of the color images, whether an image region including a target pixel whose pixel value is to be interpolated is a periodic region in which pixel values vary periodically. A first generating unit generates pixel values of the respective colors of a pixel using a first interpolation method. A second generating unit generates pixel values of the respective colors of a pixel using a second interpolation method. A control unit determines which one of the first and second generating units is to be used for generating pixel values of the respective colors of the target pixel. A pixel value combining unit combines candidate pixel values which are the pixel values of the respective colors of the target pixel to calculate a combined pixel value.