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Webvision: Color Perception <br />rFi rq 5. he IMimsel! top showi. 4 �jpelo <br />The <br />three dimensions of the Munsell colour system are: <br />Page 4 of 18 <br />1. Hue: Related to wavelength or dominant wavelength. Hue is denoted by a combination of <br />letters and numbers making up a 100 step scale (figure 5). There are ten letter categories used to <br />.denote hue, with each of these further subdivided (by the use of numerals 1 to 10) into ten <br />subgroups. If the numeral denoting the hue subgroup is 5, then it can be omitted (eg. 5R is the <br />same hue as R). <br />2. Value: Value is specified on a numerical scale from 1 (black) to 10 (white) and this attribute is <br />related to reflectance and luminosity (or lightness). <br />3. Chroma: Chroma is the Munsell term corresponding to saturation. It is indicated numerically <br />on a scale of 0 to the various maxima dependent on the saturation obtainable with available pig <br />ments. <br />For example, a colour may have a notation 2GY 6/10. This means it is a green/yellow that is quite close <br />to being a yellow; it has a value of 6 (ie. almost midway in the black/white scale) and a chroma of 10 (ie. <br />it is saturated). <br />The scaling used in the Munsell system is designed to be perceptually uniform. In another words, the <br />colour samples are arranged in equal visual steps. For example, the perceived difference between a <br />chroma of 3 and a chroma of 4 is (nominally) the same as the perceived difference between chroma 4 <br />and 5. This scaling is the same for all three dimensions, although step sizes along different dimensions <br />are not comparable (that is, a single step difference in hue does not have the same perceptual difference <br />as a single step in saturation). <br />A schematic representation of the Munsell system is shown in figure 6. The value scale is on the vertical <br />axis, the hue scale is on the perimeter of"the cylinder and chroma is on a radial scale. The Munsell top, <br />shown in Figure 5, is a more precise representation of this concept. <br />http://www.webvision.med.utah.edu/KallColor.html 6/18/01 <br />