Abstract

Chromatic discriminations were measured on two critical axes: one on tritan lines where the excitation level of S-cones varied at fixed L/M cone ratios, and the other along lines radiating from the point (1, 0) in CIE coordinates, in which the L/M ratio varied at fixed S-cone excitation levels. Color discrimination thresholds were measured on a color monitor for 20 starting colors with a dark surround or with an equiluminant white or yellow surround. Discriminations on L/M cone lines were best when the color was near the L/M cone excitation balance and were not affected by S-cone excitation level. The level of L/M cone excitation had no effect on discriminations by S-cones. When the S-cone discriminations were plotted as a function of the S-cone excitation of the starting color, the curve for the dark surround showed a basic TVI template. Discrimination with the yellow or white surrounds was better than discrimination for a dark surround when the S-cone excitation level of the starting color was near that of the surround. A further experiment indicated that S-cone discrimination for the colors whose S-cone excitation level was the same as the white surround was impaired when a gap was introduced between the starting colors and the white surround.

© 1990 Optical Society of America