1959 年 28 巻 12 号 p. 681-687
Heterochromatic brightness of colored samples is measured with Munsell value scale standards. The samples are divided into two groups: one is of medium luminous reflectance and the other of high luminous reflectance. Contour lines of the ratios of observed heterochromatic brightness L to luminous reflectance Y are drawn on C. I. E. (x-y) chromaticity diagrams by inter-and extra-polation methods. The differences between the observed data and the data obtained in previous investigations are found very small in the direction of -β axis. This is considered explainable on the one hand by the displacement of luminosity curve and on the other by the theory of color vision that the sensitivity of three receptors are non-linear in color perception.