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Chapter 17:
Light-Reflection Model
Abstract
Excerpt The Neugebauer equation is perhaps is best-known light-reflection model developed to interpret the light-reflection phenomenon of the halftone printing process. It is solely based on the light-reflection process with no concern for any absorption or transmission. Thus, it is a rather simple and incomplete description of the light and colorant interactions. However, it has been widely used in printing applications, such as color mixing and color gamut prediction, with various degrees of success. In mixing three subtractive primaries, Neugebauer recognized that there are eight dominant colors, namely, white, cyan, magenta, yellow, red, green, blue, and black for constituting any color halftone print. A given color is perceived as the integration of these eight Neugebauer dominant colors. The incident light reflected by one of the eight colors is equal to the reflectance of that color multiplied by its area coverage. The total reflectance is the sum of all eight colors weighted by the corresponding area coverage. Therefore, the Neugebauer equation is based on broadband additive color mixing of the reflected light. 17.1 Three-Primary Neugebauer Equations A general expression of the three-primary Neugebauer equation is P 3 =A w P w +A c P c +A m P m +A y P y +A cm P cm +A cy P cy +A my P my +A cmy P cmy , where P3 represents a total reflectance from one of the broadband RGB colors by mixing three CMY primaries, and Pw, Pc, Pm, Py, Pcm, Pcy, Pmy, and Pcmy are the reflectance of paper, cyan, magenta, yellow, cyan-magenta overlap, cyan-yellow overlap, magenta-yellow overlap, and three-primary overlap measured with a given additive primary light. The parameters Aw, Ac, Am, Ay, Acm, Acy, Amy, and Acmy are the area coverage by paper, cyan, magenta, yellow, cyan-magenta overlap, cyan-yellow overlap, magenta-yellow overlap, and three-primary overlap, respectively.