Page:Method for constructing the natural scale of pure color (Nutting, 1909).djvu/13

 A METHOD FOR CONSTRUCTING THE NATURAL SCALE OF PURE COLOR.

The color sensation is known to vary far from uniformly with the wave length of the exciting radiation. In a normal spectrum the variation is much more rapid in the yellowish-orange and bluish-green regions than in the midgreen or in the extreme red and violet. Hence, a color scale of say one unit for each 10 μμ difference in wave length would represent far from equal color steps. The difference in wave length just perceptible as a difference in color is roughly 5 μμ in the two most sensitive regions, 15 μμ in the midgreen, and much greater in the violet and red. The method here described makes use of data on this difference limen.

Given the least perceptible difference (difference limen) for an eye throughout the visible spectrum, the reciprocal will be proportional to color sensibility as a function of wave length. But sensibility is the derivative of a scale-reading curve, in this case the color scale desired. A method based on this principle will be applied to some of the best recent data on difference limen to illustrate the construction of a color scale.

Steindler has recently published data on the difference limen of twelve subjects having normal color vision. The characteristics of the color limen curve are shown in the figure. It has two deep minima at about 490 μμ and 580 μμ, a maximum in the green at 535 and a slight maximum and minimum at either end. The location and heights of these seven maxima and minima are given for each of the twelve subjects in the following table: 89