There has been a problem of causing too large a failure in extrapolated portions due to the multiple linear regression analysis or the 3*3 matrix optimization. An interpolation is performed to find a reduced Lab range and a reduced Lab gamut corresponding to a reduced RGB range and a reduced RGB gamut. The reduced RGB range and the reduced RGB gamut are compressed so that an RGB range and an RGB gamut are fit into an RGB gamut. A magnification ratio α is found for each grid according to relationship between the reduced Lab gamut and a Lab gamut. Then, a magnification ratio for the surface of the reduced Lab range is assumed to be that for the surface of the reduced Lab gamut. The reduced Lab range is enlarged to provide a Lab range. A magnification ratio α′ is found according to the relationship between the surface of the Lab range and the reduced Lab range. When a grid exists in the reduced Lab gamut, the magnification ratio α is used to enlarge the Lab value of the grid and provide the Lab range. When the grid does not exist in the reduced Lab gamut, the grid is enlarged by using the magnification ratio α′ to create an ICC profile.
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