An acousto-optic colorimeter for color psychophysics

Abstract

A complete model of human color perception requires the ability to present any color as a stimulus.Most existing measurements were collected with physical color samples, and current laboratory generators, such as displays and multi-primary LED systems, work with a small number of fixed primaries. Published color-difference data therefore cover about 40\% of the CIE~$xy$ chromaticity diagram, while commercial wide-gamut displays already reach two thirds of it and need difference metrics there. We describe an acousto-optic colorimeter that lets the experimenter choose the primaries. The device selects up to four narrow bands from a supercontinuum (white-light) laser, each with electronically set wavelength and intensity, and covers 95\% of the CIE~$xy$ chromaticity diagram. Threshold-scale color differences, presented in alternation as in a discrimination experiment, are reproduced with a mean error of 0.08--0.12 CIEDE2000 units ($ΔE_{00}$) at five CIE-recommended color centers. Because one color can be built from many combinations of narrow bands, the bands are chosen for the task: the finest adjustment for color matching, the least disagreement between observers for color-difference measurement. In simulations with 151~individual observers from a published dataset, with these bands observers see colors 0.6--1.9~$ΔE_{00}$ from the intended one on average, against 1.2--2.5~$ΔE_{00}$ on a calibrated wide-gamut LCD, lower at every center. The approach applies to any narrowband source and lets experimenters use saturated colors while limiting the effect of individual differences in color vision.