Discrimination of colors by red–green color vision-deficient observers through digitally generated red filter

Previous studies have shown that with the use of tinted lenses (or colored filters), individuals with red-green color vision deficiency (CVD) report an improvement in their performance on certain color vision tests. In this context, this study examines the effects of a digitally generated red-colored filter and identifies the mechanism mainly responsible for the changes in red-green CVD observers' performance on a D-15 arrangement test performed using the filter. We simulate the red filter digitally with the spectral transmittance similar to that of the X-Chrom, which is a red-tinted lens. Fourteen red-green CVD subjects are subjected to the D-15 test on a computer monitor under four filter conditions, consisting of one condition without the filter and three conditions with the filter, corresponding to the opacity of the red filter. The results show that while the simulated red filter improves the performance of deutans to arrange the caps in the D-15 test, this is not the case for protans. In addition, considerations based on the human cone-contrast model enable us to identify that the improvement in deutan observers largely results from the increase in the luminance contrast between stimuli and a background. To summarize, the red filter simulated in this study induces different changes in the red-green CVD observer luminance contrast between the protan and deutan types, with the result that the performance of deuteranopes improves while that of protanopes deteriorates.