Page:NBS Circular 553.djvu/15

 and the elimination of the double terms blue-green, purple-blue, and red-purple. Unlike the terms green and blue, which are hue names applying to all lightnesses and saturations, the term yellow is commonly used to designate not only a certain hue range but also a high lightness range within this hue range. Dark colors of the same hue as yellow are commonly called olive or olive brown. Common usage limits the term orange even more strictly; it is taken to refer not simply to a range of yellow-red hues but also to a medium- lightness range and a high saturation range. Colors of the same hue but of lower lightness and saturation than the orange range are called browns. To follow common usage in this respect, there is included a series of hue names applicable to dark colors only, as follows: reddish brown, brown, yellow- ish brown, olive brown, olive, and olive green. As a further concession to common usage, there is also included the following series of hue names appli- cable to very light colors only: purplish pink, pink and yellowish pink. The chief series of hue names to which these two subsidiary series have been fitted follows closely the 20-point division recommended by I. H. Godlove but now consists of 17 hue ranges resulting from the changes recommended by the present committee. The terms brownish pink and brownish orange have been added. The chief series now includes the names red, reddish orange, orange, orange yellow, yellow, greenish yellow, yellow green, yellowish green, green, bluish green, greenish blue, blue, purplish blue, violet, purple, reddish purple, and purplish red. The total number of designations has been reduced from 319 in 1939 to 267 in the present revision. 4.4. Some Unavoidable Disadvantages A frequent objection to this system of color desig- nations is that each designation refers to a group of distinguishable colors rather than to a single color. Since there are about ten million surface colors dis- tinguishable in daylight by the trained human eye and less than 300 color designations in this system, it is obvious that the average color range denoted by a single designation must contain nearly 40,000 distinguishable colors. If it is important to make distinctions among some of these thousands of colors bearing by this system identical designations, resort must be had to one of the many numerical systems of color specification available. Preeminent among these is the colorimetric coordinate system recom- mended in 1931 by the International Commission on Illumination (CIE) [16, 24, 53]. A corollary to this objection is that there are many pairs of easily distinguishable colors which receive by this system the same designation, while there are also many pairs that can scarcely be distinguished which receive different designations. This property is, of course, an unavoidable result of dividing the color solid into an arbitrary number of blocks, one for each of the 267 designations. Analogous dis- advantages result from identifying the time of events according to date; two events occurring on the same 4 other hand two scarcely separable midnight events may have to be assigned different dates. Just as identifying the time of an event by giving the date has proved to be useful, so it is with a system of color designations such as this. 5. Definition of the Color Ranges The definitions of the boundaries of the 267 color name blocks or ranges have been carried out by the subcommittee of the Inter-Society Color Council in terms of the Munsell renotations [41, 42] which approximate more closely the ideal psychological color system than does the 1929 edition of the Munsell Book of Color. The subcommittee checked the color boundaries by observation of all of the color standards obtain- able for which Munsell renotations were available. These included the chips of the Munsell Book of Dictionary of Color [44], the ninth edition of the Color [42], some of the chips of the Maerz and Paul Standard Color Card of America published by the Textile Color Card Association of the United States Inc. [54], and the Color Harmony Manual [11]. The boundaries for the color-name blocks found by the subcommittee to accord with common usage are given in 31 color-name charts (pages 16 to 31). They are more complicated than those of the original ISCC-NBS system and differ impor- tantly from one level of Munsell value to another. The changes of the boundaries with Munsell value are shown in seven constant-value charts (pages 31 to 34) on which the Munsell hue is indicated in the 100-point scale. The chart for value 4.75 refers to colors of medium lightness and shows 17 hue ranges, the other constant-value charts refer to lighter or darker colors than the first chart as in- dicated by their respective value notations. The value levels of these charts were picked so that every different hue or chroma boundary in the 31 color- name charts would show on one of them. The hues are indicated on these constant-value charts by the abbreviations shown in table 1. TABLE 1.-Abbreviations for the hue names used in the ISCC- NBS system Name red reddish orange. orange_ orange yellow_ yellow. greenish yellow. yellow green. yellowish green. green. bluish green. greenish blue_ blue_ purplish blue. violet. Abbre- viation R ro 0 OY Y gY YG yG G bG gB pB Name purple_ reddish purple. purplish red purplish pink. pink. yellowish pink. brownish pink. brownish orange_ reddish brown_ brown__ yellowish brown_ olive brown_. olive- olive green. Abbre- viation rP PR pPk Pk y Pk brPk bro rBr Br y Br OlBr ΟΙ OIG
 * date may be separated by many hours, but on the