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

Since there is much achromatic information in an actual visual environment, the effect of color on visibility must be considered when estimating the visibility of signs, objects, and lighting in the environments. We investigated the relationship between the recognizable threshold of form perception and three color factors (value, hue and chroma) by conducting an experiment using Landolt's eye chart of 14 color conditions under three levels of background luminance. We measured the individual visual acuity of six subjects in two age groups (young and aged). When the test chart contrast was more than 0.5, only the value affected the recognizable threshold of form perception; the chroma and hue had no effect regardless of the background luminance or individual visual acuity. Therefore, two concepts defined in our earlier studies, "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 colored target contrast is 0.5 or higher. The concepts do not hold if the target contrast is less than 0.5 because of the effect of color identification.