1. A method for determining lattice points to be referenced to prepare correspondence defining data that defines correspondence between the amount of each ink used by the printing apparatus and the color component value in a color system, said method comprising: referencing the original correspondence defining data which previously prescribes correspondence between the lattice points in the low-dimensional color space prescribed by less color components than the number of inks and the lattice points for ink amount in the ink amount space, thereby acquiring correspondence between the lattice points in the low-dimensional color space and the lattice points in the device-independent color space; prescribing a smoothness evaluation function which evaluates the 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; 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 referencing the original correspondence defining data, thereby associating the amount of each ink corresponding to the lattice points in the low-dimensional color space in the optimized state with the lattice points in the low-dimensional color space prescribed by the original correspondence defining data.