Printing CIELAB images on a CMYK printer using trilinear interpolation

Abstract

The Color Rendering project at IBM Almaden Research Center is examining the problem of how to display and print quality color images. For this work we need a printer calibrated to a device independent color space. In this paper, we describe a system for printing CIELAB images on a CMYK printers, and focus particularly on calibration methods. We use tri-linear interpolation to convert CIELAB colors to CMY or CMYK colorants. We obtain the interpolation table by inverting a tetrahedral linear interpolation of a calibration table constructed by measuring printed color patches. Since tetrahedral interpolation has a simple analytical inverse, we can produce the inverted table much more quickly than with the numerical methods needed to invert a multilinear interpolation, even though we have to measure more patches to obtain the same accuracy. To cover the full printer gamut, we found it necessary to add some out-of-gamut entries to the inverted interpolation table. These entries must be obtained by extrapolation, and increase the errors interpolating colors on and near the gamut surface. To date we have calibrated a DuPont 4Cast to print CIELAB colors using CMY colorants. We discuss our results with this calibration, how we propose to add black, and how we fit gamut mapping into the processing.