Page:Journal of the Optical Society of America, volume 33, number 7.pdf/4

 finally the colors of the identification tests. In each instance, no mention is made of the normality of the observer’s color vision (1), or of the conditions of lighting or viewing.

Agitation toward research for the development of a suitable system of color terminology was begun in the twenties by E. N. Gathercoal, then a member of the USP Revision Committee (2). After the founding of the Inter-Society Color Council, of which he was the first chairman, studies were made of the then existing color systems, and in 1933 the report (3) was submitted which became the basis of the system of color names now known as the ISCC-NBS system of color names (4). Procedures were developed at the same time for the application of these color names to the description of the colors of crude drugs, powdered drugs, chemicals, liquids, precipitates, microscopic structures, and fluorescent materials (5). The central notations of the color-name blocks were determined for the application of these color names to the description of the colors of soils (6). Recently these names have also been used to describe the colors of illuminants and a description of this method of use is in preparation.

In all of this work, the boundaries of the separate color-name blocks have been specified in terms of the Munsell color standards (7), (8). It was realized early in the project that in order to be placed on a sound basis the individual boundaries must be specified in fundamental terms. The accuracy of the system of color names would then be independent of the existence or stability of the individual system of material color standards in terms of which the system is used in practice. Since the Munsell color system provided a very satisfactory means of determining which color name best described the color of an object, it was decided to measure the spectral reflectances of all of the color standards in the Munsell Book of Color. The specification of the trilinear coordinates and apparent reflectances of each of the Munsell samples would provide an invariable specification of the color of that sample and thereby of a definite point in the framework of the system by which the relative position of each color name is indicated. Tristimulus specifications of the Munsell Book of Color have been published by Glenn and Killian (8) and were available for some time before that date. Instead of using the Glenn-Killian data, however, it seemed preferable to define the ISCC—NBS system of color names by way of the Munsell samples actually used in the color-names work. This involved a nominal repetition of the spectrophotometric and colorimetric work carried out by Glenn and Killian, but avoided uncertainties arising out of the possible differences between the respective Munsell samples bearing the same color designation as well as those arising from the unknown history and usage of the Glenn-Killian samples prior to their measurement. Furthermore, the present authors desired to use in the spectrophotometric measurements certain methods of calibration regularly used at the National Bureau of Standards for such work. The measurements and computations described below were accordingly undertaken, and the diagrams and tables included in the present paper provide a means by which a color may be named without reference to a color chart, or by which the boundaries of the color-name blocks may be specified in terms of a fundamental color system. It is now possible to select the appropriate color name for a color when the fundamental specifications for that color are given.

Since the application of this system of color names will be made in the plant or in the field where the illumination used will usually be daylight, all of the techniques and computations both for the color names and for the Munsell system have primarily been made on the basis of ICI Illuminant C. However, colorimetric data on the Munsell standards for other illuminants are also of interest. Accordingly, based on the same spectrophotometric data, tristimulus values have been computed for four illuminants—ICI Illuminant C (9) (representative of average daylight), ICI Illuminant A (9) (2842°K (10), representative of incandescent illuminants), IIluminant D (11), (12) (representative of lightly overcast north sky), and Illuminant S (13), (14) (representative of extremely blue sky).