Effects of three color factors on recognizable threshold of form perception taking into account individual differences of visual abilities

Since there is much achromatic information in actual visual environments, the effect of color on visibility must be considered when estimating the visibility of signs, objects, and lighting. The authors examined the relationship between the recognizable threshold of form perception and the three color factors (lightness, hue, and chroma) by conducting experiments using Landolt ring visual acuity test charts of 14 color conditions under three levels of background luminance. In the experiments, the visual acuity of six subjects in two age groups (young and elderly) was measured. When the test chart luminance contrast is 0.5 or above, only the lightness affects the recognizable threshold of form perception, and the chroma and hue have no effect regardless of the background luminance or individual visual acuity. Therefore, two concepts defined in our earlier studies, the "visual acuity ratio" (to the maximum level of individual visual acuity) and "relative acuity" (incorporating individual visual acuity into the target size), hold if the luminance contrast of chromatic visual targets is 0.5 or higher. However, the concepts do not hold if the contrast is less than 0.5 due to the individual differences in color discrimination abilities.