Figure 5.

Trade-off between discrimination and constancy. (Left) Each set of connected solid circles shows the trade-off between and for various optimizations of the steepness parameter n (see the text). Each set is for a different noise level (σ_n = 0.01, 0.025, 0.05, 0.075, 0.10), with the set closest to the upper right of the plot corresponding to the lowest noise level. The reference illuminant had intensity e_ref = 100, and the test illuminant had intensity e_test = 160. The surface ensemble was specified by μ_r = 0.5 and σ_r = 0.3 and was common to both the reference and test environments. Both and were evaluated with respect to draws from this surface ensemble. The gain parameter was held fixed at g = 0.02045. The steepness parameter for the reference environment was n = 4.5. Parameters g = 0.02045 and n = 4.5 optimize discrimination performance for the reference environment when σ_n = 0.05. The open circles connected by the dashed line show the performance points that could be obtained for each noise level if there were no trade-off between discrimination and constancy. (Right) Equivalent trade-off noise plotted against visual noise level σ_n. See the discussion in the text.