Rumi YAMAUCHI, Mitsuo IKEDA and Hiroyuki SHINODA

Department of Photonics, Faculty of Science and Engineering, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan

(Received June 19, 2002; Accepted February 17, 2003; Revised February 7, 2003)

The apparent color of an object depends on how we recognize the space where it is placed in terms of illumination. We call this the recognized visual space of illumination (RVSI). What we see in the space first, namely, the initial visual information (IVI) determines properties of the RVSI, and we will show in this paper that the walls surrounding this space are the most important IVI for the construction of the RVSI. A normal room was illuminated by a ceiling light at 60 lx and its central area was also lit by a hidden illumination of 400 lx. Two halves of a miniature room with walls on three sides and a floor were inserted from left and right sides into the hidden illumination to gradually create one miniature room, and the apparent lightness of a test patch was judged as a function of the amount of the inserted portions to measure construction of RVSI for the hidden illumination. The apparent lightness was around 55 in L^* when no IVI was in the hidden illumination, it gradually went down with more IVI to around 40 L^* to return toward its nominal lightness of 24 L^* in the case of test patch N2. The drop was large with the present condition of IVI where, in the end, the space of the hidden illumination was surrounded by walls, compared to the previous results where the space was filled only by objects; this indicated the importance and efficiency of walls for constructing RVSI.

Key words: lightness, apparent lightness, lightness constancy, color appearance, color constancy, spotlight, hidden illumination, recognized visual space of illumination, enclosed space, Gelb effect