A processor estimates a shape of a subject on the basis of an image of the subject, and a memory stores the shape of the subject. The processor generates a quadratic surface connecting a plurality of points on the subject on the basis of the shape of the subject, and develops each of the plurality of points to a planar surface contacting the quadratic surface. Thereafter the processor corrects the image of the subject on the basis of a position of each of the plurality of points developed to the planar surface.