Anomalous trichromats' judgments of surface color in natural scenes under different daylights

Abstract

Deuteranomalous trichromacy, which affects medium-wavelength-sensitive cones, is more common than protanomalous trichromacy, which affects long-wavelength-sensitive cones. The aim of the present work was to test the extent to which these two kinds of anomalous trichromacy affect surface-color judgments in the natural world. Simulations of 18 natural scenes under different daylight illuminants were presented on a high-resolution color monitor to 7 deuteranomalous, 7 protanomalous, and 12 normal trichromatic observers, who had to discriminate between reflectance and illuminant changes in the images. Observers' ability to judge surface color was quantified by a standard color-constancy index. Deuteranomalous trichromats performed as well as normal trichromats, but protanomalous trichromats performed more poorly than both. The results are considered in relation to the spectral coverage of cones, rod intrusion, and the characterization of anomalous trichromacy by the Rayleigh match.

Figure 1

Detectability of changes in surface color during daylight illuminant changes for one normal trichromat (a and b), and two anomalous trichromats; one protanomalous trichromat (P6: see table 1) (c and d), and one deuteranomalous trichromat (D4: see table 2) (e and f). The frequency of “illuminant change” responses, pooled across 18 natural scenes for each observer, is plotted as a function of the chromaticity of a local illuminant simulating a reflectance change of a test surface embedded in the scene. The square symbols show the first illuminant, a daylight with correlated color temperature of 25000 K in (a), (c) and (e), and 4000 K in (b), (d) and (f), and the circles the second illuminant, 6700 K. The triangle shows the mode (and where large enough the bars show ±1 SE). The daylight locus (L) and the protanopic (P) and deuteranopic (D) confusion lines are also shown.

Figure 2

Detectability of changes in surface color during daylight illuminant changes for normal trichromats (a and b), protanomalous trichromats (c and d) and deuteranomalous trichromats (e and f). The frequency of “illuminant change” responses, pooled across observers within each group for one sample scene, is plotted as a function of the chromaticity of a local illuminant simulating a reflectance change of a test surface embedded in the scene. Other details as for Fig. 1.

Figure 3

Color-constancy index as a function of matching range in Rayleigh anomaloscopy. Data are for protanomalous trichromats with first illuminant 25000 K and first illuminant 4000 K , and for deuteranomalous trichromats with first illuminant 25000 K and first illuminant 4000 K .The dotted line is a linear regression, with slope equal to 0.065 and SE of 0.022.