To easily generate a base LUT in which correspondence relation among RGB image data, CMYK image data, and color values is described while securing precision.

Lattice points in an RGB color solid are omitted by a method, and colors of an image are measured as to the remaining lattice points to set the base LUT. One object lattice point is selected first, CMYK image data at the object lattice point are interpolated with CMYK image data at lattice points adjacent to the object lattice point, and interpolation errors are calculated. Only lattice points having small interpolation errors are omitted. Thus, the lattice points are omitted while it is confirmed that CMYK image data are obtained with sufficient precision even by the interpolation, and then the lattice points can be omitted without impairing the precision, and then the accurate base LUT can easily be set.