Color calibration

A printing system comprising:

• a printing device to print a plurality of inks;
• a print controller to receive print job data;
• and
• a memory comprising:
• a color-mapping look-up table to map a first set of n-dimensional color input points to a corresponding second set of n-dimensional color output points, the color-mapping look-up table representing a measured behavior of the printing system;
• and
• a color calibrator to:
• determine a filter mapping function of color input points that satisfies a first predetermined optimization condition based on a first mapping error between the filter mapping function and the color mapping, the first mapping error being a function of individual errors between:
• outputs of the filter mapping function as applied to respective color input points in the first set of color input points;
• and
• corresponding color output points from the second set of color output points as mapped from the respective color input points by the color mapping;
• determine a smoothed mapping function of color input points that satisfy a second predetermined optimization condition based on a second mapping error between the smoothed mapping function and entries of the color-mapping look-up table, the second mapping error being a function of individual errors between:
• outputs of the smoothed mapping function as applied to respective color input points in the first set of color input points;
• and
• corresponding color output points from the second set of color output points as mapped from the respective color input points by the color-mapping look-up table;
• and
• generate a calibrated color-mapping look-up table based on the smoothed mapping function,
• wherein the second predetermined optimization condition is a third predetermined optimization condition and the second mapping error is a third mapping error, the third mapping error between the smoothed mapping function and the color mapping being evaluated using a subset of the first set of color input points that excludes color input points that do not satisfy a predetermined error condition based on the outputs of the filter mapping function as applied to the respective color input data points,
• wherein the print controller is configured to use the calibrated color-mapping look-up table to print the print job data using the printing device.