CALIBRATING DIGITAL HALFTONING ALGORITHMS WITH MULTIPLE PERSONALITIES

A method, apparatus, and article of manufacture for updating the calibration of a printer or printers which use multiple calibration functions. The method comprises the steps of applying the first calibration function to grayscale commands to obtain modified grayscale commands, printing the grayscale patches with the modified printing commands, and measuring the resulting grayscale values. Using this data, an updated printer calibration function t(i) is generated such that mapping the printer commands through t(i) results in printed grayscales substantially matching the commanded grayscales. Then, the updated printer calibration function t(i) is used to update the printer calibration function f(i) to obtain g(i). The apparatus comprises a means for obtaining modified grayscale commands by applying a first calibration function, a printer to print grayscale patches with the modified printing commands, and a scanner or densitometer for measuring the resulting grayscale values. The apparatus also comprises a means for obtaining an updated printer calibration function and a means for deriving an updated function g(i) based on the updated printer calibration function. In an alternative embodiment, the foregoing is used to update scanner calibration.