A technique is disclosed to calculate a new pixel value of a particular color of second-viewpoint color image data in such a manner that a difference between the new pixel value of the particular color of the second viewpoint and the pixel value of the particular color of the first-viewpoint color image data maintains correlation with a sum of a difference between the pixel value of a first color component of the second-viewpoint color image data and the pixel value of the first color component of third-viewpoint color image data and a difference between the pixel value of a second color component of the second-viewpoint color image data and the pixel value of the second color component of the third-viewpoint color image data.