Reducing the number of calibration patterns for the two-by-two dot centering model

The two-by-two dot centering model enables predicting the spectral reflectance of color halftones and does not depend on a specific halftoning algorithm. It requires measuring the reflectances of a large number of two-by-two calibration tile patterns. Spectral measurement of hundreds or thousands of tile patterns is cumbersome and time consuming. In order to limit the number of measurements, we estimate the reflectances of a large majority of twoby-two calibration tile patterns from a small subset comprising less than 10% of all tile patterns. Using this subset of measured two-by-two calibration tile patterns, we perform a linear regression in the absorptance space and derive a transformation matrix converting tile pattern colorant surface coverages to absorptances. This transformation matrix enables calculating the absorptance of all remaining two-by-two tile patterns. For a cyan, magenta and yellow print, with 72 two-by-two measured calibration tile patterns, we are able to create a two-bytwo dot centering model having an accuracy only slightly below the accuracy of the model with the fully measured set of 1072 two-by-two tile patterns.