Perceived Saturation in Normal and Red–Green Color‐Deficient Observers

ABSTRACT To directly compare the strength of perceived saturation between color‐normal observers (CNOs) and congenital red–green color‐deficient observers (CDOs), the perceived saturation differences of 11 test pairs were evaluated by CNOs, protans, and deutans using a grayscale method. Three experiments were conducted. First, the commonality of lightness‐difference evaluation on the grayscale was examined. Results for three color vision types were nearly identical, indicating the effectiveness of the method. Second, to individually prepare equal‐brightness stimuli for each of the four hue series (Red, Green, Yellow, and Blue), a brightness‐matching experiment was conducted. CDOs showed the Helmholtz–Kohlrausch effect similar to CNOs, except for the Red series, where the effect was weaker than CNOs. Third, the perceived saturation difference of the test pair with different chroma but nearly the same hue and brightness was evaluated. It increased with the Δ E 00 of the test pair similarly in all hues in individual observers and thus fitted by a linear equation. The mean slopes for CNOs, protans, and deutans were 1.01, 0.79, and 0.60, respectively, reflecting the relative strength of perceived saturation difference. On the other hand, the group data showed hue dependency that the decrease of perceived saturation difference relative to CNOs was larger in Red and Green than Yellow and Blue, indicating greater reduction in the red‐green mechanism than the yellow‐blue. No significant difference was found between protans and deutans, or between dichromats and anomalous trichromats in this study, but that requires further investigation.