VISUAL DETERMINATION OF SUPRATHRESHOLD COLOR-DIFFERENCE TOLERANCES USING PROBIT ANALYSIS

As part of a research program to improve the relationship between visual and numerical color-difference evaluation for industrial colorimetry, a color-difference tolerance data set for fitting and testing of color-difference metrics has been extended to include 156 individual color-tolerance determinations. These tolerances were designed to sample 19 color centers over a surface color gamut with balanced sampling of lightness and chromaticness differences. The tolerance determination procedures emphasized accurate estimation of population visual color-difference response and rigorous estimation of tolerance precision. Tolerance accuracy was confirmed by excellent agreement of these results and the majority of previous experiments on five color centers selected for CIE color-difference evaluations. The average uncertainty of the tolerance determinations was +/- 11% of the tolerance value at a 2-sigma-level (95% confidence interval). The completed data set is suitable for estimating the parameters of color-difference metrics or testing the performance of such metrics. The color tolerances indicated the systematic lack of uniformity of the CIELAB space, in general agreement with previous experiments. A simple modification of the CIELAB color-difference metric was shown to account for much of the systematic lack of uniformity.