An Experimental Determination of Some Iso-Chromaticity Lines in Color-Deficient Vision*

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Abstract
From an assortment of red and red-purple Munsell papers, 47 color-deficient and 13 color-normal subjects selected matches for eight standard blue-green and neutral papers. The color-deficient subjects were classified into the following groups: 7 protans with severe defects, 9 protans with mild defects, 10 deutans with severe defects, and 21 deutans with mild defects. For every subject the three colors (one at each of three chroma levels) chosen as matches for each standard were plotted on the CIE diagram, and a straight line, originating at the locus of the standard color, was fitted through the points. The slopes of these lines are significantly different for protans and deutans. Color-deficient subjects with mild defects tend to select the same matches as do those with severe defects, but the former show more variability. In addition, matches made by subjects with severe defects are more often rated “good” or “excellent,” and are more likely to fall along a straight line than are those made by subjects with mild defects. Matches made by the colornormal subjects are most variable and never rated good. Data on the constants of the iso-chromaticity lines, the Munsell notations of the matches, and the lightness relationships are given. For all matches by deutans and for matches against neutral standards by protanopes, the agreement of the empirical lines with those predicted from spectral data by Judd is good. However, protan matches against blue-green standards diverge markedly from predictions; protans actually select colors which are yellower than those predicted from spectral data. When the data for all value levels are pooled, it appears that the iso-color lines for some subjects may be curved rather than straight.
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