In the medical field, it is sometimes the case that when a region of interest exists on an image obtained by a given modality, a corresponding region is identified on an image obtained by another modality, and diagnosis is then performed based on the comparison between them. If imaging posture differs between modalities, the shape of the object differs at the times of imaging. This makes it difficult to identify the object. Under the circumstance, attempts have been made to estimate the deformation of an object between modalities (that is, alignment between images accompanying deformation). This makes it possible to estimate the position of a corresponding region based on the position information of a region of interest and to generate an image by deforming one image so as to have the same shape as that of the other image.
NPL 1 discloses a technique of facilitating the comparison between the shapes of an object before and after its deformation by normalizing the shape of the object accompanying deformation. More specifically, there is disclosed a method of calculating the geodesic distance matrix of the surface shape of an object and normalizing the surface shape by using a multidimensional scaling method using the calculated matrix. This method can normalize the shape of an object which deforms without changing the geodesic distance matrix of the object surface so as to allow direct comparison between the shapes of the object before and after the deformation. This makes it possible to easily compare the deformed shapes of an object accompanying deformation and recognize the object based on its shape.