Image processing apparatus and image processing method

An image processing apparatus for obtaining difference information between two planar images A and B acquired at two different time points, the planar images being produced based on data indicative of transmission amounts of X-rays transmitted through an object, wherein an X-ray imaging apparatus radiates the X-rays to the object and detects the transmitted X-rays as the data, the image processing apparatus comprising:

• first registration means for producing two planar images fa and gb by applying a registration process to overall areas of the two planar images A and B based on curves decided from positions designated on the two planar images A and B respectively, wherein the registration process is performed such that the positions which are set on each of the planar images A and B are aligned along a straight line, both the straight lines corresponding to each other in a horizontal direction, and a scale factor for the registration is changed position by position on the straight lines;
• second registration means for searching one of the two planar images, gb, produced by the first registration means, for a match of each of a plurality of local regions composing the other planar image fa, to any of regions of the one planar image gb, and re-projecting images of the matched regions to produce a planar image hb;
• and
• difference calculating means for calculating the difference information between the planar image hb produced by the second registration means and the other planar image fa produced by the first registration means.