The brightness of chromatic stimuli

We present the results of a series of three brightness-matching experiments which include a key refinement in this established psychophysical method. Constraining the chroma difference between pairs of stimuli matched in brightness allows us to use a novel calculus-based approach to building a model of the brightness of chromatic visual stimuli and the Helmholtz-Kohlrausch effect. The proposed models, compatible with the CIECAM16 color appearance model and CIELAB color space, are compared to other models of the Helmholtz-Kohlrausch effect on these data and other past brightness-matching studies. The proposed CIECAM16-based model demonstrates the overall best performance on predicting the Helmholtz-Kohlrausch effect in four newer data sets but overpredicts the weaker effect reported in three older data sets. The potential experimental factors in this divide between new and old studies are also discussed.