On the Causes of Differences between the Colour-Matching Functions of Physiological Systems of Trichromats and Dichromats

Abstract

The article discusses the reasons for the differences between the colour-matching functions (CMF) of the physiological trichromat system (LMS)phys1 and the cone fundamentals of the CIEPO06 colorimetric system and the CMF of Nyberg-Yustova colorimetric system (LMS)NY1. It has been shown that the hypothesis, which has prevailed for many years, that dichromatism is caused by the absence of one of the trichromat’s receptors, cannot explain the difference in spectral sensitivity of L-, M- and S-type cones of trichromats and dichromats. It is shown that the CIEPO06 and (LMS)NY functions can be obtained from the (LMS)phys CMF of trichromats if the algorithm for determining reference colour stimuli in dichromats is based on a dominant receptor detecting signals from a neighbouring receptor with reduced sensitivity. The results obtained indicate that protanopes have almost no L-cones, and therefore the sensitivity of their long-wavelength M-receptors matches that of trichromat’s M-cones. This demonstrates that the algorithm for forming the long-wavelength reference colour stimulus M in protanopes aligns with the hypothesis that they lack trichromat’s L-cones. A different result was observed for deuteranopes. The contribution of M-cone signals to the sensitivity of deuteranope L-cones exceeds 40 %. This is why the measured spectral sensitivity of their L-receptors differs significantly from that of normal trichromat’s L-receptors. This result suggests that using the CIEPO06 functions as spectral sensitivities for trichromats is not justified. Since the algorithms for forming reference colour stimuli in the human visual system vary among trichromats, protanopes, and deuteranopes, the authors suggest introducing three different physiological colorimetric systems: one for trichromats based on (LMS)phys, and separate systems for protanopes and deuteranopes based on CIEPO06.