Munsell color system
In colorimetry, the Munsell color system is a color space that specifies colors based on three properties of color: hue, chroma, and value. It was created by Professor Albert H. Munsell in the first decade of the 20th century and adopted by the United States Department of Agriculture as the official color system for soil research in the 1930s.
Several earlier color order systems had placed colors into a three-dimensional color solid of one form or another, but Munsell was the first to separate hue, value, and chroma into perceptually uniform and independent dimensions, and he was the first to illustrate the colors systematically in three-dimensional space. Munsell's system, particularly the later renotations, is based on rigorous measurements of human subjects' visual responses to color, putting it on a firm experimental scientific basis. Because of this basis in human visual perception, Munsell's system has outlasted its contemporary color models, and though it has been superseded for some uses by models such as CIELAB and CIECAM02, it is still in wide use today.
Explanation
The system consists of three independent properties of color which can be represented cylindrically in three dimensions as an irregular color solid:- hue, measured by degrees around horizontal circles
- chroma, measured radially outward from the neutral vertical axis
- value, measured vertically on the core cylinder from 0 to 10
Hue
Each horizontal circle Munsell divided into five principal hues: Red, Yellow, Green, Blue, and Purple, along with 5 intermediate hues halfway between adjacent principal hues. Each of these 10 steps, with the named hue given number 5, is then broken into 10 sub-steps, so that 100 hues are given integer values. In practice, color charts conventionally specify 40 hues, in increments of 2.5, progressing as for example 10R to 2.5YR.Two colors of equal value and chroma, on opposite sides of a hue circle, are complementary colors, and mix additively to the neutral gray of the same value. The diagram below shows 40 evenly spaced Munsell hues, with complements vertically aligned.
Value
Value, or lightness, varies vertically along the color solid, from black at the bottom, to white at the top. Neutral grays lie along the vertical axis between black and white.Several color solids before Munsell's plotted luminosity from black on the bottom to white on the top, with a gray gradient between them, but these systems neglected to keep perceptual lightness constant across horizontal slices. Instead, they plotted fully saturated yellow, and fully saturated blue and purple along the equator.
Chroma
Chroma, measured radially from the center of each slice, represents the “purity” of a color, with lower chroma being less pure. Note that there is no intrinsic upper limit to chroma. Different areas of the color space have different maximal chroma coordinates. For instance light yellow colors have considerably more potential chroma than light purples, due to the nature of the eye and the physics of color stimuli. This led to a wide range of possible chroma levels—up to the high 30s for some hue–value combinations. Vivid solid colors are in the range of approximately 8.| Note that the Munsell Book of Color contains more color samples than this chart for both 5PB and 5Y. However, they are not reproducible in the sRGB color space, which has a limited color gamut designed to match that of televisions and computer displays. There are no samples for values 0 and 10, which are theoretical limits not reachable in pigment, and no printed samples of value 1. |
Specifying a color
A color is fully specified by listing the three numbers for hue, value, and chroma in that order. For instance, a purple of medium lightness and fairly saturated would be 5P 5/10 with 5P meaning the color in the middle of the purple hue band, 5/ meaning medium value, and a chroma of 10.History and influence
The idea of using a three-dimensional color solid to represent all colors was developed during the 18th and 19th centuries. Several different shapes for such a solid were proposed, including: a double triangular pyramid by Tobias Mayer in 1758, a single triangular pyramid by Johann Heinrich Lambert in 1772, a sphere by Philipp Otto Runge in 1810, a hemisphere by Michel Eugène Chevreul in 1839, a cone by Hermann von Helmholtz in 1860, a tilted cube by William Benson in 1868, and a slanted double cone by August Kirschmann in 1895. These systems became progressively more sophisticated, with Kirschmann’s even recognizing the difference in value between bright colors of different hues. But all of them remained either purely theoretical or encountered practical problems in accommodating all colors. Furthermore, none was based on any rigorous scientific measurement of human vision; before Munsell, the relationship between hue, value, and chroma was not understood.Albert Munsell, an artist and professor of art at the Massachusetts Normal Art School, wanted to create a “rational way to describe color” that would use decimal notation instead of color names, which he could use to teach his students about color. He first started work on the system in 1898 and published it in full form in A Color Notation in 1905.
The original embodiment of the system had some deficiencies as a physical representation of the theoretical system. These were improved significantly in the 1929 Munsell Book of Color and through an extensive series of experiments carried out by the Optical Society of America in the 1940s resulting in the notations for the modern Munsell Book of Color. Though several replacements for the Munsell system have been invented, building on Munsell's foundational ideas—including the Optical Society of America's Uniform Color Scales, and the International Commission on Illumination’s CIELAB and CIECAM02 color models—the Munsell system is still widely used, by, among others, ANSI to define skin and hair colors for forensic pathology, the USGS for matching soil colors, in prosthodontics during the selection of shades for dental restorations, and breweries for matching beer colors.