The position of each color chip is then calculated by standard trigonometric functions. To position color chips on the second and third hue dimensions, each of the 40 hues has been positioned around the circumference of the globe, beginning with 5.0 red at 0°, moving clockwise 9° for each of the other 39 hues. The value measure for each color chip has been assigned to first dimension. To construct quantitative measures on the Munsell color structure, the Munsell spherical coordinates have been transformed into standard Cartesian coordinates. We think it reasonable to assume that the Munsell axes approximate the true perceptual axes of hue and value not only because of the scaling results, but also because hue complements and negative afterimages are found on opposite sides of the Munsell space, exactly as they should be given the basic assumptions of opponent process theory ( 1). A number of scaling studies have confirmed the approximately equal perceptual spacing of color chips and the overall organization of the system ( 5).
Based on millions of human judgments, the OSA estimated the best-fitting Commission International de l'Eclairage (CIE) colorimetric positions for each of the Munsell color chips so that the entire set would conform as closely as possible to the Munsell conceptual system ( 4). The two systems have similar hue axes, one axis extending from yellow to purple-blue, the other from red to blue-green ( 1, 2). 1).ĭiagrammatic representation of the Munsell color solid with one quarter section removed.Īlthough there are a variety of systems for ordering colors, so far as we are aware, only the Munsell and Optical Society of America (OSA) systems are based on extensive direct judgments of perceptual similarity. The full sample of color chips in the Munsell book of color form an irregular sphere with notable protuberances in the yellow and red regions (see Fig. The chroma scale runs in equal perceptual intervals from 0 (achromatic) to 16 or more (highly saturated). Right angle distance from the value axis represents degree of saturation, labeled chroma. Each sector is further divided into four subdivisions, labeled 2.5, 5.0, 7.5, and 10.0, with the best exemplar color for each hue sector at 5.0. Circling the equator of the globe are the hues, divided into 10 equally distant sectors labeled red, yellow-red, yellow, green-yellow, green, blue-green, blue, purple-blue, purple, and red-purple. The vertical dimension, called value, runs in equal perceptual steps from white to black. The goal of the Munsell system is to present an arrangement of a full sample of colors in equal perceptual intervals over the three dimensions of the color space. The Munsell system, developed by the artist Albert Munsell circa 1905, is based on a standardized set of painted color surfaces, commonly called color chips, arranged in a globe-like 3D space.
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