A method for determining lattice points to be referenced to prepare the correspondence defining data, said method including steps of prescribing a smoothness evaluation function which evaluates smoothness of arrangement of lattice points in the device-independent color space and contains a constraint condition that the arrangement of lattice points becomes nonuniform at a certain position in the device-independent color space and which has as a variable the lattice point position information in the low-dimensional color space which is prescribed by less color components than the number of inks used by the printing apparatus, optimizing the arrangement of lattice points in the device-independent color space by improving the rating of the smoothness evaluation function, with the lattice point position information in the low-dimensional color space varied, and determining lattice points to be referenced to prepare the correspondence defining data in the optimized state.