In an image processing device and image processing method in which first image data consisting of a plurality of color data and constituting image information for each pixel are input, and second image data consisting of a plurality of color data are calculated and output, after color conversion of the first image data, dither processing is applied to produce the second image data. As a result, information of the fractional part generated as a result of the color conversion is not omitted but preserved. Tone conversion may be performed after the color conversion, and before the dither processing. The image processing device or image processing method can restrain reduction in the number of colors that can be expressed, and restrain the generation of discontinuities (irregularities) in the change of data, while realizing an “exact color reproduction” or “preferred color reproduction.”