In order to accelerate the processing speed using existing hardware or program, MFP sets a reference lattice point in the device space of a printer (S05), calculates the difference between first color data and the reference lattice point (S06), sets the dimension having the largest difference of the differences of dimensions not set as process targets, as a process target dimension (S10), sets the lattice point having the process target dimension as a second process target lattice point (S11), calculates a base term based on the difference of the process target dimension, the first process target lattice point, and the second process target lattice point (S18), calculates a total sum vector (S19), resets the second process target lattice point as a first process target lattice point every time the base term is calculated (S20), calculates a second reference vector using an existing triangular pyramid interpolation expression when the number of dimensions not set as process target dimensions become three (S14), and determines second color data from the total sum vector and the second reference vector.