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 of “wave-length” or “wave-length constitution.” Color cannot be identified with or reduced to terms of any purely physical conception; it is fundamentally a psychological category.

B. .—The nature of any color can be completely specified psychologically in terms of three fundamental attributes, this specification taking the form of an immediate description of the color, as such, without any reference whatsoever to the stimulus. The names employed for these three attributes by different authorities vary widely and frequently are such as to refer not only to properties of the color but also to related properties of the stimulus. Hence it seems necessary, in the interests of unambiguous thinking, to introduce certain refinements and possibly some innovations in terminology at this point. The Committee suggests the following nomenclature.

(a) Brilliance is that attribute of any color in respect of which it may be classed as equivalent to some member of a series of grays ranging between black and white. Synonymous terms, as used by various writers, are “luminosity” (Abney, ', 4, 86) (Rood, ', 33) (Troland, ', 948), “brightness” (Luckiesh, ', 1) (Helmholtz, ', 243-245), “tint” (Titchener, ', 61-64), “value” (Munsell, ', 12-13), and “visual brightness’”’ (Nutting, ', 300).

(b) Hue is that attribute of certain colors in respect of which they differ characteristically from the gray of the same brilliance and which permits them to be classed as reddish, yellowish, greenish, or bluish. There is a very satisfactory agreement among authorities regarding the usage of this term, which seems not to have been corrupted by any definite physical application.

(c) Saturation is that attribute of all colors possessing a hue,