Printer calibration adjusting NPac vector based on measurement data

A printing system comprising:

• a printing device to print a calibration area onto a print substrate, the calibration area corresponding to a given colorant in a set of colorants printable by the printing system;
• a measurement interface to receive an indication of a measured optical property of the printed calibration area;
• a memory comprising a vector in an area coverage space, the vector defining a statistical distribution of colorant combinations including a first colorant combination over an area of a halftone;
• and
• a print controller to modify the vector on the basis of the measured optical property by decreasing a contribution to the vector of the first colorant combination and increasing a contribution to the vector of a second colorant combination, the second colorant combination differing from the first colorant combination by a predetermined amount of the given colorant.

A non-transitory computer-readable storage medium comprising a set of computer-readable instructions that, when executed by a processor of a printing system, cause the processor to:

• receive measured optical data indicating a measured optical property of a printed test area formed from a given printing fluid in a set of printing fluids useable by the printing system;
• and
• calibrate the printing system by modifying, based on the optical property of the printed test area, a Neugebauer Primary area coverage (NPac) vector,
• wherein the modifying the NPac vector comprises:
• decreasing an area coverage in the NPac vector of a first Neugebauer Primary (NP);
• and
• increasing an area coverage in the NPac vector of a second NP,
• wherein the first NP and the second NP each comprise a contribution of a printing fluid in the set of printing fluids, and
• wherein the first NP and the second NP comprise different contributions of the given printing fluid.