TheMunsell color system is acolor space that specifiescolors based on three properties of color:hue (basic color), value (lightness), andchroma (color intensity). It was created byAlbert H. Munsell in the first decade of the 20th century and adopted by theUnited States Department of Agriculture (USDA) as the official color system forsoil research in the 1930s.
Several earlier color order systems in the field ofcolorimetry had placed colors into a three-dimensionalcolor solid of one form or another, but Munsell was the first to separate hue, value, and chroma intoperceptually uniform and independent dimensions, and he was the first to illustrate the colors systematically in three-dimensional space.[1] 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basis in human visual perception, Munsell's system has outlasted its contemporary color models, and though it has been superseded for some uses by models such asCIELAB (L*a*b*) andCIECAM02, it is still in wide use today.[2]
The system consists of three independent properties of color which can be representedcylindrically in three dimensions as an irregularcolor solid:
Munsell determined the spacing of colors along these dimensions by taking measurements of human visual responses. In each dimension, Munsell colors are as close to perceptually uniform as he could make them, which makes the resulting shape quite irregular. As Munsell explains:
Desire to fit a chosen contour, such as the pyramid, cone, cylinder or cube, coupled with a lack of proper tests, has led to many distorted statements of color relations, and it becomes evident, when physical measurement of pigment values and chromas is studied, that no regular contour will serve.
— Albert H. Munsell, "A Pigment Color System and Notation"[3]
Since the first rendition of the Munsell color system, each horizontal circle is divided into five principalhues:Red,Yellow,Green,Blue, andPurple, along with 5 intermediate hues between adjacent principal hues:YR,GY,BG,PB, andRP.[4] Despitetrichromatic color being best described with 3primary colors or 4unique hues, Munsell chose to define his color space with 5 principal hues to keep itdecimalized.[5] Munsell describes the intermediate hues as orange, grass green, peacock blue, violet and plum,[6] but opts to simplify the notation with the portmanteaus of the principal colors for the sake of intuition.[7]
In later renditions, these 10 principal and intermediate colors were further subdivided into 10 steps each, so that at least 100 hues are definable. The sub-steps are numbered 1 to 10, which prepends the hue letter(s), e.g.8GY. However, further subdivisions are possible through interpolation, e.g.8.7GY. In practice, color charts conventionally specify 40 hues, in increments of 2.5, progressing as for example 10R to 2.5YR.
| 5R | | 5YR | | 5Y | | 5GY | | 5G | | 5BG | | ||||||||||||||||||
201 130 134 | 201 130 127 | 201 131 118 | 200 133 109 | 197 135 100 | 193 137 94 | 187 140 86 | 181 143 79 | 173 146 75 | 167 149 72 | 160 151 73 | 151 154 78 | 141 156 85 | 127 159 98 | 115 160 110 | 101 162 124 | 92 163 134 | 87 163 141 | 82 163 148 | 78 163 154 | 73 163 162 | |||
| 5BG | | 5B | | 5PB | | 5P | | 5RP | | 5R | | ||||||||||||||||||
73 163 162 | 70 162 170 | 70 161 177 | 73 160 184 | 82 158 189 | 93 156 193 | 104 154 195 | 117 151 197 | 128 149 198 | 141 145 198 | 152 142 196 | 160 140 193 | 168 138 189 | 177 135 182 | 183 134 176 | 188 132 169 | 193 131 160 | 196 130 153 | 198 130 146 | 200 130 140 | 201 130 134 | |||
Value, orlightness, varies vertically along the color solid, from black (value 0) at the bottom, to white (value 10) at the top.[8] 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 (light), and fully saturated blue and purple (dark) along the equator.
Chroma, measured radially from the center of each slice, represents the "purity" of a color (related tosaturation), with lower chroma being less pure (more washed out, as inpastels).[9] 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 thenature 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 (though it is difficult or impossible to make physical objects in colors of such high chromas, and they cannot be reproduced on current computer displays). Vivid solid colors are in the range of approximately 8.
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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 (lightness), and a chroma of 10 (see swatch). Anachromatic color is specified by the syntaxN V/. For example, a medium grey is specified by "N 5/".
In computer processing, the Munsell colors are converted to a set of "HVC" numbers. The V and C are the same as the normal chroma and value. The H (hue) number is converted by mapping the hue rings into numbers between 0 and 100, where both 0 and 100 correspond to 10RP.[10]
As the Munsell books, including the 1943 renotation, only contains colors for some points in the Munsell space, it is non-trivial to specify an arbitrary color in Munsell space.Interpolation must be used to assign meanings to non-book colors such as "2.8Y 6.95/2.3", followed by aninversion of the fitted Munsell-to-xyY transform. The ASTM has defined a method in 2008, but Centore 2012 is known to work better.[11]
The idea of using a three-dimensionalcolor 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 byTobias Mayer in 1758, a single triangular pyramid byJohann Heinrich Lambert in 1772, a sphere byPhilipp Otto Runge in 1810, a hemisphere byMichel Eugène Chevreul in 1839, a cone byHermann von Helmholtz in 1860, a tilted cube by William Benson in 1868, and a slanted double cone byAugust Kirschmann in 1895.[12] 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.[12]
Albert Munsell, an artist and professor of art at the Massachusetts Normal Art School (nowMassachusetts College of Art and Design, or MassArt), wanted to create a "rational way to describe color" that would use decimal notation instead of color names (which he felt were "foolish" and "misleading"),[13] 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 inA Color Notation in 1905.
The original embodiment of the system (the 1905 Atlas) had some deficiencies as a physical representation of the theoretical system. These were improved significantly in the 1929Munsell Book of Color and through an extensive series of experiments carried out by theOptical Society of America in the 1940s resulting in the notations (sample definitions) for the modernMunsell 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'sUniform Color Scales, and theInternational Commission on Illumination'sCIELAB (L*a*b*) andCIECAM02 color models—the Munsell system is still widely used, by, among others,ANSI to defineskin color andhair color forforensic pathology, theUSGS for matchingsoil color,[14] inprosthodontics during the selection oftooth color fordental restorations, andbreweries for matchingbeer color.[15][16][b]
The original Munsell color chart remains useful for comparing computer models of human color vision.[17]
He wanted to use a decimal system making each step divisible by 5 or 10—a system which is easy to understand and easy for computer programming and cataloging. That's why Munsell used 5 principal hues—red, yellow, green, blue and purple—instead of the seven colors in the visible spectrum (ROY G BIV).
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For the vision capacities of organisms or machines, see  Color vision. | |