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DECEMBER, 1940

J. O. S. A.

VOLUME 30

An Analysis of the Original Munsell Color System

John E. Tyler AND Arthur C. Hardy

Massachusetts Institute of Technology, Cambridge, Massachusetts

IN 1919, the Munsell Color System was subjected to a spectrophotometric examination by Priest, Gibson, and McNicholas,^[1] who determined the spectral reflection characteristics of fifteen chromatic standards and nine neutral standards of the system. These spectrophotometric data have now been integrated in accordance with the 1931 I.C.I. standard observer and Illuminant C. The resulting tristimulus values and trichromatic coefficients are listed in Table I.

Table I. Tristimulus specifications (X, Y, Z) and trichromatic coefficients (x,y) of 15 Munsell Atlas colors computed from spectrophotometric data (1919) on the basis of the I.C.I. standard observer and coordinate system and for I.C.I. Illuminant C,

Munsell Notation		X	Y	Z	x	y
R	7/5	0.4951	0.4399	0.4305	0.3626	0.3221
	5/5	.2768	.2140	.1713	.4101	.3276
	3/2	.0977	.0878	.0809	.3667	.3295
Y	7/4	.4661	.4869	.2625	.3835	.4006
	5/5	.2605	.2662	.1024	.4141	.4232
	3/2	.0950	.0974	.0708	.3611	.3700
G	7/4	.4173	.4860	.4688	.3041	.3542
	5/5	.1811	.2454	.1982	.2899	.3928
	3/2	.0766	.0933	.0952	.2888	.3519
B	7/4	.4325	.4827	.6573	.2750	.3070
	5/5	.2246	.2595	.4385	.2434	.2813
	3/2	.0822	.0904	.1412	.1412	.2620
P	7/3	.5162	.4978	.6613	.3081	.2972
	5/5	.2773	.2448	.4187	.2948	.2602
	3/2	.0981	.0921	.1553	.2838	.2667

The instructions given by Professor Munsell for making a pigment color-solid are so complete that the entire color system can be constructed, given any five chromatic colors of the system which are unrelated in the sense that no two have either the same hue or complementary hues. The definitions of hue, value, and chroma are unambiguously established by the operations involved in constructing the system by means of additive mixtures on a Maxwell disk.^[2] The hue, value, and chroma of such a mixture are related to those of the components of the mixture as follows:

Hue.—When a chromatic color is mixed additively with a neutral (white, gray, or black), the hue of the mixture is the same as that of the chromatic color.

Value.—When two colors whose values are $V_{a}$ and $V_{b}$ ; occupy relative areas a and b on a Maxwell disk, the value of the mixture is given by the equation $V^{2}=aV_{a}^{2}+bV_{b}^{2}$ .

Chroma.—When two complementary colors occupy areas on a Maxwell disk which are inversely proportional to the product of value by chroma, a neutral gray results.

By comparison of these quantities with the corresponding quantities in psychophysical systems, it is evident that hue is synonymous with dominant wave-length, that value is the square root of luminous apparent reflectance, $Y$ , expressed in percent, and that, for a given hue and value, chroma is proportional^[3] to colorimetric purity in psychophysical systems.

Table II. Tristimulus specifications (X,Y,Z) and trichromatic coefficients (x,y) of the five principal Munsell colors taken from Table I, each set of tristimulus specifications being multiplied by a factor to make Y=0.2500.

Munsell Notation	X	Y	Z	x	y
R 5/5	0.31298	0.25000	0.20018	0.4101	0.3276
Y 5/5	.21634	.25000	.09613	.4141	.4232
G 5/5	.24459	.25000	.20198	.2899	.3928
B 5/5	.18454	.25000	.42235	.2434	2813
P 5/5	.28326	.25000	.42761	.2948	.2602

When tristimulus specifications have been assigned to five unrelated colors in the Munsell system, the calculation of the tristimulus specifications for all other colors in the system involves no more than a hypothetical repetition of the procedure employed originally by Professor Munsell. In other words, the disk mixtures of Professor Munsell can be made hypothetically by the I.C.I. observer under carefully standard-

↑ Tech. Paper No. 167, Bur. Stand. (1919).
↑ These operations are partly described in Chapter V of A Color Notation, by A. H. Munsell (Ellis, Boston, 1907), and the description is completed in the Atlas of the Munsell System (Wadsworth-Howland, Malden, Massachusetts,
↑ During his early work, Professor Munsell defined chroma in such a manner that when a chromatic color is mixed with a neutral on a Maxwell disk, the chroma of the mixture is less than that of the chromatic color in proportion to the fraction of the area of the disk occupied by the neutral. The type of color system to which this definition leads is discussed in a bachelor’s thesis by John E. Tyler on file in the Library at the Massachusetts Institute of Technology.

[1] Tech. Paper No. 167, Bur. Stand. (1919).

[2] These operations are partly described in Chapter V of A Color Notation, by A. H. Munsell (Ellis, Boston, 1907), and the description is completed in the Atlas of the Munsell System (Wadsworth-Howland, Malden, Massachusetts,

[3] During his early work, Professor Munsell defined chroma in such a manner that when a chromatic color is mixed with a neutral on a Maxwell disk, the chroma of the mixture is less than that of the chromatic color in proportion to the fraction of the area of the disk occupied by the neutral. The type of color system to which this definition leads is discussed in a bachelor’s thesis by John E. Tyler on file in the Library at the Massachusetts Institute of Technology.

[1]

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