When converting image data constituted by a plurality of objects to data for an output device, color appearances of object images specified as a same output color are set so as to not vary even when their respective background colors vary. A color appearance model forward conversion section uses forward conversion of a color appearance model to calculate target appearance colors, which are targets of appearances of objects based on color information of the objects. A surrounding adaptive background color obtaining section generates surrounding adaptive background colors based on pixels around a pixel of interest for object images that have undergone rendering. Then, output pixel values of the pixel of interest are calculated by a color appearance model reverse conversion section using reverse conversion of the color appearance model based on the target appearance color and the surrounding adaptive background colors.