Hunter system, Munsell

Fig. 3.4b), known as CIELAB, has generally replaced the Hunter space for industrial applications although this has been somewhat slower in parts of the food industry where methods established on the Hunter system have economic reasons for its continued use. The improvements in CIELAB are due to the nonlinear cube root transformation of the 1931 tristimulus values, which more approximate the visual spacing of the coloured samples in the Munsell system. The formulae are... 

Three attributes characterize color hue, lighmess (or value), and saturation (or chroma) and they are graphically represented in color solids (e.g., Munsell solid. Hunter solid). The Munsell Color Notation is a rapid, portable, widespread, and economical system of color determination. However, as it depends on sensory evaluation by panels, many laboratories prefer when possible to replace human judgment by instrumental techniques that are easier to handle. The CIELAB established by the Commission International d Eclairage (CIE) has become widely used with the availability of reflectance spectrophotometric instrumentation. 

Equal Euclidean distances in the CIE-Yxy system are not necessarily perceived by a human observer as equal color distances. To match Euclidean and perceived distances, a wide variety of so-called uniform color spaces has been developed (Hunter and Harold, 1987). One of the first of these uniform systems was developed in the early 1900 s by the artist A.H. Munsell. Starting with the observation that brighter hues like yellow and red create a much stronger color sensation at color saturation than darker hues like blue or green, he mounted color chips on a rotating Maxwell disk to... 

Note that the uniformity of a color space is of concern only if color is regarded as a (visual) quality. When using color as an analytical tool, the color system which differentiates the iron oxides most effectively would be the most favorable, no matter whether it is uniform or not. A discriminant analysis performed with a large number of iron oxide samples showed that CIE-Yxy, CIE-Lab, and the Munsell system performed equally well (Scheinost and Schwertmann, 1999). Therefore, the choice of a color system is not crucial. Furthermore, computer programs are available which transfer colors from one system into another. More details on color theory and color systems are given by Wyszecki and Styles (1982) and Hunter and Harold (1987). 

The Hunter tristimulus colorimeter represents a departure from the usual colorimeters, as it presents its data in a form closely akin in spacing to the Munsell system. By resistance networks between a series of barrier-layer photocells which view the reflected light from a specimen through tristimulus filters and a compensating cell which views the light source, a reading is obtained which is related to perceptible differences. 

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