A print calibration system comprising a printing device to apply print material to a print target in a printing process, a memory for storing a lookup table; and a processor. The processor causes the printing device to print calibration points for reproducing a color ramp, by receiving a plurality of Neugebauer Primary area coverage (‘NPac’) points representing the plurality of calibration points and determining a hue angle and color space based on the NPac points. A plurality of nodes distributed between a first node and a second node of a sectional representation of the NPac points is determined. A lookup table is generated based on a relationship between the plurality of nodes and the NPac points for use during the printing process, wherein the lookup table comprises values to map between a first color space and a second color space, the lookup table is then provided to the printing device.