Provided is an image processing apparatus including: a first generating unit configured to generate a three-dimensional image with use of an image signal obtained by imaging an imaging target object with a radiation； a second generating unit configured to set a projection reference line in the three-dimensional image, and perform projection processing of projecting pixel values of the three-dimensional image to the projection reference line for each projection angle of a plurality of projection angles about the projection reference line, to thereby generate a plurality of pieces of projection data at the plurality of projection angles； and a third generating unit configured to two-dimensionally arrange the plurality of pieces of projection data based on the plurality of projection angles, to thereby generate a two-dimensional image.
