Categorical color constancy under RGB‐LED light sources

Abstract

The light-emitting diode (LED)-based light sources have been widely applied across numerous industries and in everyday practical uses. Recently, the LED-based light source consisting of red, green and blue LEDs with narrow spectral bands (RGB-LED) has been a more preferred illumination source than the common white phosphor LED and other traditional broadband light sources because the RGB-LED can create many types of illumination color. The color rendering index of the RGB-LED, however, is considerably lower compared to the traditional broadband light sources and the multi-band LED light source (MB-LED), which is composed of several LEDs and can accurately simulate daylight illuminants. Considering 3 relatively narrow spectral bands of the RGB-LED light source, the color constancy, which is referred to as the ability of the human visual system to attenuate influences of illumination color change and hold the perception of a surface color constant, may be worse under the RGB-LED light source than under the traditional broadband light sources or under the MB-LED. In this study, we investigated categorical color constancy using a color naming method with real Munsell color chips under illumination changes from neutral to red, green, blue, and yellow illuminations. The neutral and 4 chromatic illuminants were produced by the RGB-LED light source. A modified use of the color constancy index, which describes a centroid shift of each color category, was introduced to evaluate the color constancy performance. The results revealed that categorical color constancy under the 4 chromatic illuminants held relatively well, except for the red, brown, orange, and yellow color categories under the blue illumination and the orange color category under the yellow illumination. Furthermore, the categorical color constancy under red and green illuminations was better than the categorical color constancy under blue and yellow illuminations. The results indicate that a color constancy mechanism in the visual system functions in color categories when the illuminant emits an insufficient spectrum to render the colors of reflecting surfaces accurately. However, it is not recommended to use the RGB-LED light source to produce blue and yellow illuminations because of the poor color constancy.

Influences of lighting time course and background on categorical colour constancy with RGB‐LED light sources

“…For each chromatic illuminant, the colour naming of 240 Munsell surfaces was performed in four conditions, as shown in Table 2. It should be noted that the data in condition 4 were exactly the same as those in our previous study 24 ; they will be analyzed and discussed together with the data in the other three conditions in the present study. Figure 3 shows examples of the procedures of the following two conditions: the brief adaptation and multicolour background condition (condition 2, illustrated by panel A) and the complete adaptation and gray background condition (condition 3, panel B).…”

“…Five illuminants were obtained by adjusting the chromaticity and intensity of the RGB-LED lamp using the remote controller so that the standard white plate illuminated by it showed the desired chromaticity and luminance when measured by a spectroradiometer (PR-715, Photo Research, New York). Figure 2 shows the spectral power distributions of all the illuminants produced by the RGB-LED lamp (also see Figure 2 in the previous study 24 ).…”

“…The subjects in the present study are the same in our previous study. 24 The distribution of subjects in the experiments of the red-green and blue-yellow illuminants can be found in Table A2 (also see table A3 in the previous study). Seven subjects (#1~#7, four males and three females, age 22-25 years) participated in the experimental sessions under red and green illuminants, three of the participants (subjects #5, #6, and #7) and another two subjects (#8 and #9), for a total of five subjects (four males and one female, age 24-31 years) participated in the sessions under the blue and yellow illuminants.…”

“…The experimental setup and the RGB-LED light source used in the present study are the same as those in our previous study. 24 The experiment was performed in a viewing cabinet (36 cm high × 36 cm wide × 36 cm deep) located in a dark room. The inner walls and floor of the cabinet (not the ceiling) were covered with gray paper with a spectral reflectance of approximately 25%.…”

“…F I G U R E 2 This figure is the same as figure 2 in the previous study. 24 Normalized spectral power distributions of all illuminants produced by the RGB-LED lamp. The curves of the red, blue, and yellow illuminants overlap with each other at a peak of approximately 625 nm…”