1. An image processing device comprising: a studying image acquisition unit configured to acquire a studying image group including an image pair of a first-quality image and a second-quality image with different image qualities; a tentative eigenprojection matrix generation unit configured to generate a provisional tentative eigenprojection matrix from the acquired studying image group by a projection computation; a tentative projection core tensor creation unit configured to create a tentative projection core tensor defining a correspondence between the first-quality image and an intermediate eigenspace and a correspondence between the second-quality image and the intermediate eigenspace from the acquired studying image group and the generated tentative eigenprojection matrix; a first tentative sub-core tensor creation unit configured to create a first tentative sub-core tensor corresponding to a condition specified by a first setting from the created tentative projection core tensor; a first tentative subtensor projection unit configured to project at least one of the first-quality image and the second-quality image in the studying image group by a first projection computation using the tentative eigenprojection matrix and the first tentative sub-core tensor to calculate a coefficient vector in the intermediate eigenspace; a representative vector calculation unit configured to obtain a representative intermediate eigenspace coefficient vector, which represents the coefficient vector group, from the coefficient vector group calculated by the first tentative subtensor projection unit in accordance with the number of studying representatives; a representative studying image group determination unit configured to determine a representative studying image group from the representative intermediate eigenspace coefficient vector obtained by the representative vector calculation unit; an eigenprojection matrix generation unit configured to generate an eigenprojection matrix from the determined representative studying image group by the projection computation; and a projection core tensor creation unit configured to create a projection core tensor defining a correspondence between the first-quality image and the intermediate eigenspace and a correspondence between the second-quality image and the intermediate eigenspace from the determined representative studying image group and the eigenprojection matrix generated by the eigenprojection matrix generation unit.