Visualization of Expanded Printing Gamuts Using 3-Dimensional Convex Hulls

Abstract: A 3-D convex hull program, Qhull, was applied to data sets consisting of the Neugebauer primaries and selected multicolor traps of 4-, 5- and 6-color printing systems. Program output was plotted as polytopes, curved surface solids or wireframes in CIE Lab space in full color. These produced a 3-D representation of a lithographic printing gamut. Superposition of two or more gamuts affords users full color visual feedback of where, what color and how much color enhancement was brought about by changes of inks or stocks. These techniques provide far more detail than traditional 2-D gamut plots. Quantitative estimates of gamut volumes compared the color reproduction potential of several sets of fluorescent process printing inks. The input of many hundreds of halftone data points from IT8 charts were processed with the same ease as a sparse set of Neugebauer primaries. This produced a more accurate gamut on convex surfaces and some improvement in the accuracy in volumes. Background Hallmark Cards has a long history of process printing with 6-color, wide gamut, ink systems. Research into the use of fluorescent colors in Hallmark's 6-color ink systems began in 1960 with imported fluorescent pigments from Germany. Formulation work was done in cooperation with Acme Inks, now INX International, in Chicago. By 1962 Hallmark was commercially printing greeting cards with six process inks, three of which included fluorescent colorants, a fluorescent pink, a fluorescent yellow and a fluorescent magenta. A non-fluorescent light cyan was also used. The blue-shade, process pink aided in printing delicate pastel highlights and pale skin tones. At the midtones a fluorescent magenta was brought into the separation until a full solid of magenta and pink ended the scale. Combining the pink-magenta solid with yellow ___________