The Munsell Color System
All colors can be fully specified in terms of their hue, lightness and saturation. The Munsell system has three dimensions: hue, value and chroma. These three dimensions correspond to the three perceptual attributes of human color vision.
The three dimensions of the Munsell color system are:
1. Hue: Related to wavelength or dominant wavelength. Hue is denoted by a combination of letters and numbers making up a 100 step scale (figure 21). There are ten letter categories used to denote hue, with each of these further subdivided (by the use of numerals 1 to 10) into ten subgroups. If the numeral denoting the hue subgroup is 5, then it can be omitted (eg. 5R is the same hue as R).
2. Value: Value is specified on a numerical scale from 1 (black) to 10 (white) and this attribute is related to reflectance and luminosity (or lightness).
3. Chroma: Chroma is the Munsell term corresponding to saturation. It is indicated numerically on a scale of 0 to the various maxima dependent on the saturation obtainable with available pig ments.
For example, a color may have a notation 2GY 6/10. This means it is a green/yellow that is quite close to being a yellow; it has a value of 6 (ie. almost midway in the black/white scale) and a chroma of 10 (ie. it is saturated).
The scaling used in the Munsell system is designed to be perceptually uniform. In another words, the color samples are arranged in equal visual steps. For example, the perceived difference between a chroma of 3 and a chroma of 4 is (nominally) the same as the perceived difference between chroma 4 and 5. This scaling is the same for all three dimensions, although step sizes along different dimensions are not comparable (that is, a single step difference in hue does not have the same perceptual difference as a single step in saturation).
A schematic representation of the Munsell system is shown in figure 22. The value scale is on the vertical axis, the hue scale is on the perimeter of the cylinder and chroma is on a radial scale. The Munsell top, shown in Figure 21, is a more precise representation of this concept.
Figure 22 (a) Munsell color system (illustrating hue, value and chroma)
Figure 22 (b) Schematic diagram of the three axes of the Munsell color system