<title>Gray component replacement by direct colorimetric mapping</title>

Abstract

A new gray component replacement approach for four-color printing process is developed to directly convert CIE XYZ values into CMYK values. We start with building a colorimetric density lookup table (LUT) for black channel from 0 to 255 (for 8-bit per-channel). A color in CIE XYZ color space is converted into colorimetric density, then the colorimetric density is compared with colorimetric densities in the black densities LUT to find maximum black. The actual black is determined based on the maximum black that has been found. The remaining of the total colorimetric density subtracted from the colorimetric density of the actual black is converted into CIE XYZ value, and finally the CIEXYZ value is converted into CMY by a predictive printer color mixing model. A close-up correction algorithm is implemented to reduce color errors coming from both the CIE XYZ to CMYK inversion and the assumption that the colorimetric density is additive.