Discrimination ellipsoids of aperture and simulated surface colors by Matching and paired comparison

Discrimination ellipsoids were constructed in the (x, y, Y ) space for six colors s o : achromatic, red, yellow, green, blue, and brown. the colors were presented on the surround, either dark (aperture color mode) or bright (simulated surface color mode). Ellipsoids were defined by two methods: matching and paired comparison (an extended form of the method of constant stimuli). Hence, four ellipsoids were obtained with s o by each of two observers. For simulated surface colors, except for the yellow color, the two methods gave almost the same ellipsoids. Ellipsoids defined by the fluctuation of matches were almost the same for both aperture and simulated surface colors. Those ellipsoids are similar on the chromaticity diagram to ellipses estimated through MacAdam's colormetric coefficients g's. Paired comparisons were more difficult for aperture colors than for simulated surface colors in the sense that the ellipsoids were larger in size. However, the rates of false discrimination for identical pairs (s o , s o ) were higher for surface colors. In spite of the drastic change of appearance of the brown color, no change was observed between the two modes of appearance for ellipsoids obtained by either method. the study is methodological and detailed statistical analyses of the two data processings are included, one based on matchings and the other based on paired comparisons.