In some examples, the memory 130 comprises a lookup table mapping colorimetric values with vectors in the area coverage space. For example, the lookup table may map RGB or CMYK color values to NPac vectors. In some examples, the lookup table maps XYZ, LAB or any other color space used to specify the device color space. Where the vectors comprise NPac vectors, the lookup table may be referred to as a “HANS lookup table”. When an RGB mapping is used, the HANS lookup table may comprise 17³ entries. When a CMYK mapping is used, the HANS lookup table may comprise 9⁴ entries. The vector 160 may correspond to an entry in the HANS lookup table.

The print controller 140 is arranged to modify the vector 160 on the basis of the measured optical property. The print controller 140 is arranged to modify the vector 160 by decreasing a contribution to the vector 160 of the first colorant combination and increasing a contribution to the vector 160 of a second colorant combination. The second colorant combination differs from the first colorant combination by a predetermined amount of the given colorant.