|The Munsell Color System
One of the most influential color-modeling systems was devised by Albert Henry Munsell, an American artist. Munsell desired to create a "rational way to describe color" that would use clear decimal notation instead of a lot of color names that he considered "foolish" and "misleading." His system, which he began in 1898 with the creation of his color sphere, or tree, saw its full expression with his publication, A Color Notation, in 1905. This work has been reprinted several times and is still a standard for colorimetry (the measuring of color).
Munsell modeled his system as an orb around whose equator runs a band of colors. The axis of the orb is a scale of neutral gray values with white as the north pole and black as the south pole. Extending horizontally from the axis at each gray value is a gradation of color progressing from neutral gray to full saturation. With these three defining aspects, any of thousands of colors could be fully described. Munsell named these aspects, or qualities, Hue, Value, and Chroma.
Munsell defined hue as "the quality by which we distinguish one color from another." He selected five principle colors: red, yellow, green, blue, and purple; and five intermediate colors: yellow-red, green-yellow, blue-green, purple-blue, and red-purple; and he arranged these in a wheel measured off in 100 compass points:
The colors were simply identified as R for red, YR for red-yellow, Y for yellow, etc. Each primary and intermediate color was allotted ten degrees around the compass and then further identified by its place in the segment. For example, primary red would be identified as 5R since it stands at the mid-point of the red segment. 2.5R would be a red tending more toward red-purple, while 7.5R is a red tending more toward yellow-red.
Munsell's arrangement of colors in this way was also important for his concept of color harmony, or balance. Munsell was a conservative artist with strict views on the aesthetics of painting. He wanted his system to serve not only as guide for notating colors, but as a guide for choosing complimentary colors for artistic work.
Value was defined by Munsell defined value as "the quality by which we distinguish a light color from a dark one." Value is a neutral axis that refers to the grey level of the color. This ranges from white to black. As notations such as 10R, 5YR, 7.5PB, etc. denote particular hues, the notation N is used to denote the gray value at any point on the axis. Thus a value of 5N would denote a middle gray, 2N a dark gray, and 7N a light gray. In Munsell's original system, values 1N and 9N are, respectively, black and white, though this was later expanded to values of 0 (black) through 10 (white).
The value of a particular hue would be noted with the value after the hue designation. For example, 5PB 6/ indicates a middle purple-blue at the value level of 6.
It should be noted, too, that Munsell's scale of value is visual, or perceptual. That is, it's based on how we see differences in relative light, not on a strict set of mathematical values from a light source or illuminant.
Chroma is the quality that distinguishes the difference from a pure hue to a gray shade. The chroma axis extends from the value axis at a right angle and the amount of chroma is noted after the value designation. Thus 7.5YR 7/12 indicates a yellow-red hue tending toward yellow with a value of 7 and a chroma of 12:
However, chroma is not uniform for every hue at every value. Munsell saw that full chroma for individual hues might be achieved at very different places in the color sphere. For example, the fullest chroma for hue 5RP (red-purple) is achieved at 5/26:
Another color such as 10YR (yellowish yellow-red) has a much shorter chroma axis and reaches fullest chroma at 7/10 and 6/10:
In the Munsell System, reds, blues, and purples tend to be stronger hues that average higher chroma values at full saturation, while yellows and greens are weaker hues that average fullest chroma saturation relatively close to the neutral axis. And, reds, blues, and purples reach fullest saturation at mid-levels on the value scale, while yellows and greens reach it at higher values (7/- or 8/-).
The result of these differences is that what Munsell originally envisioned as a sphere or orb is radically asymmetrical. A three-dimensional solid representation of Munsell's system would look like the following:
This gave rise to the alternate describing the solid representation as a tree.
Munsell's system, although dating back to the 19th century and devised more by intuition than exact science, is still an internationally accepted, leading color system. The Munsell Book of Colors is sold commercially to printers and designers, as are a number of other Munsell color products.
Also available are digital color libraries for Munsell Book of Colors and Munsell High Chroma Colors. These libraries are available in Adobe PageMaker and Adobe FrameMaker and can be found in some other drawing and layout programs as well. However, as we will point out again later, any digital color library will not display accurately due to the gamut constraints of RGB. You can only match colors accurately using printed swatches supplied by companies such as Munsell.
The Munsell company, founded by A.H. Munsell in 1918, is currently owned by GretagMacbeth and can be found on the Web at www.munsell.com.