The use of four process inks (CMYK) is common practice in the graphic arts, and provides the foundation for many output device technologies. In commercial applications the number of inks are sometimes extended beyond the process inks depending on the customers' requirements, and cost constraints. In InkJet printing extra inks have been used to both extend the color gamut, and/or improve the image quality in the highlight regions by using "light" inks. The addition of "light" inks are sometimes treated as an extension of the existing Cyan or Magenta inks, with the Cyan tone scale smoothly transitioning from the light to the dark ink as the required density increases, or are sometimes treated independently. If one is to treat the light ink as an extension of the dark ink, a simple blend can work well where the light and dark inks fall at the same hue angle, but will exhibit problems if the light and dark inks hues deviate significantly. The method documented in this paper addresses the problem where the hues of the light and dark inks are significantly different. An ink interaction model is built for the light and dark inks, then a composite primary is constructed that smoothly transitions from the light ink to dark ink, preventing the blended ink from over inking, while ensuring a smooth transition in lightness, chroma, and hue. The method was developed and tested on an XES (Xerox Engineering Systems) ColorGraphx X2 printer, on multiple substrates, and found to provide superior results to the alternative linear blending techniques.
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