Ken-ichiro KAWAMOTO^1,*, Taisuke INAMURA¹, Hirohisa YAGUCHI^1,2 and Satoshi SHIOIRI^1,2

¹Graduate School of Science and Technology, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
²Department of Information and Image Sciences, Faculty of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

(Received January 9, 2003; Accepted August 1, 2003; Revised May 28, 2003)

We investigated color discriminability on the background color. The measurement was carried out at over 21 background colors in (L, M) plane of a cone space by four observers. We used low temporal stimulus frequency (1 Hz) so that threshold was determined by the red-green opponent mechanism. Results showed that color discriminability depends on the background colors. Threshold was higher with a more saturated background color. This suggests that the sensitivity of the red-green opponent mechanism is high when the mechanism's output is small and increases with the output levels of the mechanism. To confirm this relationship between the red-green mechanism and color discriminability, color appearance depending the background color was also evaluated. There was a strong correlation between the sensitivity and the perceived whiteness. Both sensitivity and whiteness value were highest at around the equal energy white point and decreased with increase in the difference between background color and equal energy white. This suggests that the adaptation state of the red-green opponent color controls color discrimination.

Key words: color discrimination threshold, background color adaptation, red-green opponent mechanism, color appearance, whiteness

^*E-mail address: kawamoto@cnc.chukyo-u.ac.jp