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; an eigenprojection matrix generation unit configured to generate, from the acquired studying image group, an eigenprojection matrix by a projection computation using a local relationship; a projection core tensor creation unit configured to create, from the acquired studying image group and the generated eigenprojection matrix, a projection core tensor using locality, the 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; a first sub-core tensor creation unit configured to create, from the created projection core tensor, a first sub-core tensor corresponding to a condition specified by a first setting; a second sub-core tensor creation unit configured to create, from the created projection core tensor, a second sub-core tensor corresponding to a condition specified by a second setting; a first subtensor projection unit configured to project an input image to be processed by a first projection computation using the eigenprojection matrix and the first sub-core tensor to calculate a coefficient vector in the intermediate eigenspace; and a second subtensor projection unit configured to project the calculated coefficient vector by a second projection computation using the second sub-core tensor and the eigenprojection matrix to generate a change image with an image quality different from the input image.