Differential color thresholds and new results on failures of chromaticity and luminance prediction

Abstract

The experimental determination of differential chromaticity thresholds from metameric matches show discrepancies in colorimetric prediction using the standard observers established by the CIE (Hita et al., J Opt Soc Am A 1986; 3: 1203-09; Jimenez del Barco et al., J Optics 17, 1986; 247-54). In this work we have determined whether the discrepancies of colorimetric prediction are contained in the differential color thresholds. To study the possibility of generalizing prior results to a wider range of experimental conditions we have carried out new experiments determining the differential color thresholds of an achromatic stimulus from metameric matches, using direct vision and a foveal field of 1.5 degrees . The results are expressed in terms of the color-matching functions of CIE-2 degrees standard observer, as well as those proposed by 2 degrees -Stiles and Burch and Nayatani et al. The discussion of the results is made taking into account different causes which may explain the failures of colorimetric prediction detected: rod intrusion, interactions of the responses of cones sensitive to short-wavelengths, errors and matching imprecision. Results show that the failures of colorimetric prediction obtained under our experimental conditions exceed the color differential threshold. These discrepancies increase with the relative difference of the S-cone excitation level for the matched stimuli.