US Patent 7813576 Image processing apparatus

A difference image is obtained between two images which are objects of comparative viewing, regardless of whether the images are processed images. A judgment means judges whether the two images are processed images, based on process confirmation data attached thereto. A correction means corrects images which have been judged to be processed images by the judgment means to a state equivalent to that of the images prior to image processes. The correction is performed based on image processing condition data which are attached to the processed images. A positional alignment means aligns the positions of the two images. An inter image calculation means performs inter image calculation between unprocessed or corrected images.