色弱者を対象とした円形視標の見やすさ評価に関する検討

－カラーユニバーサルデザインのための測光色コントラスト評価図を用いた視認性推定法に関する研究(その2)－

抄録

 It is vitally important to estimate visibility of all visual targets in real environments to maintain the visual safety. As luminance images or luminous color images in real lit environments are relatively easily obtained, it is reasonable to attempt to establish a method to estimate visibilities of objects using these images.

 Authors have proposed C-A graph that can estimate visibility from luminance images using contrast profile method. In another previous study, authors have proposed a method to analyze effects of color using XYZ stimulus values and L*a*b* color space. The proposed method calculates luminous contrast values (LC, aC, bC) and luminous average values (LA, aA, bA) from XYZ stimulus values by referring to L*a*b* color space. ‘LC’ indicates the luminance contrast, ‘aC’ indicates the red-green contrast and ‘bC’ indicates the yellow-blue contrast.

 In addition, authors have conducted visibility evaluation experiments using circular objects, varying luminance and chromaticity for the common color vision type people. Circular objects and background with varying background luminance, background chromaticity, luminance contrast (LC), chromaticity contrast (aC, bC), and object size were displayed on the 27 inch digital display screen. Subjects observed circular objects displayed on uniform-luminance background with both eyes from 2500 mm point. Subjects evaluated visibilities of circular objects using 5-step scale of ‘0’ to ‘4’. ‘0’ is invisible, ‘1’ is visible with considerable effort, ‘2’ is visible with effort, ‘3’ is visible effortlessly and ‘4’ is easily visible. Experiment results were presented on CIE 1931 xy chromaticity diagram and aC-bC graph.

 In this study, same experiments were conducted for congenital protan (protanopia/protanomaly) and deutan (deuteranopia/deuteranomaly) types in order to achieve color universal design. Experiment results were analyzed using CIE 1931 xy chromaticity diagram and aC-bC graph and experiment results of common, protan, and deutan types were compared respectively. The findings of the study are listed below.

 1) When circular object size is 5 minutes, background chromaticity was D65, and luminance contrast (LC) was zero, tendencies of results of protan and deutan types were similar with those of the common type with slightly greater range in red-green direction. Visibilities of circular objects with the color range from greenish yellow to violet worsened by the effect of small-field tritanopia.

 2) The same tendency was seen in other background chromaticities.

 3) When circular object sizes became greater than 5 minutes, tendencies of results of protan and deutan types had greater range in red-green direction than those of the common type.

 4) When luminance and chromaticity contrasts were changed simultaneously, it was seen that tendencies of results of common, protan, and deutan types differed greatly. As the LC absolute values increased, visibilities of circular objects of the common type improved overall, however, those of protan and deutan types worsened in specific chromaticity contrast (aC, bC) ranges. When LC is positive (LC>0), visibilities of circular objects of the protan type worsened in contrast ranges that are redder than ‘color confusion line of S-cone’, while visibilities of circular objects of the deutan type worsened in contrast ranges that are greener than ‘color confusion line of S-cone’.

 In the next step, we will calculate color contrast values from LMS stimulus values and establish the visibility estimation method considering color vision types.