For colors with the same luminance, increasing the saturation increases the color brightness. This phenomenon, known as the Helmholtz-Kohlrausch (H-K) effect, is a characteristic of human vision. In our estimations of the H-K effect in natural images, we found that the brightness-to-luminance (B/L) ratio decreases with increasing the lightness. However, the estimation was not enough for high lightness images containing a large amount of cyan. We, therefore, propose an estimation equation considering the decreasing B/L ratio with increasing the lightness. This estimation method takes into account the characteristic that the B/L ratio is 1.0 or higher. First, we create a function that reflects the decrease of the magnitude of the H-K effect with respect to the increase of the lightness at each hue. Then, the difference between the lightness and the standard lightness (the lightness used in Nayatani's estimation equation) is multiplied. The effectiveness of the proposed method was verified in a subjective-evaluation experiment of high-lightness images containing a large amount of cyan. Moreover, the method improved the accuracy of the estimation, and we confirmed the decrease in B/L ratio with increasing the lightness by excluding B/L values below 1.0.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.