[OPTICAL REVIEW Vol. 5, No. 3 (1998) 200-205]

Three Dimensionality of the Recognized Visual Space of Illumination Proved by Hidden Illumination

Mitsuo IKEDA, Hiroyuki SHINODA and Yoko MIZOKAMI

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

(Received January 28, 1998; Accepted March 24, 1998)

We hypothesized that the recognized visual space of illumination (RVSI) was constructed in our brain when we grasped the state of illumination of a space. The importance about the RVSI is that it is three dimensional and is valid not only at the surfaces of the existing objects in the space, but also for the entire portion in the space where no objects exist. With this property of RVSI we are able to predict the appearance of an object surface in terms of lightness as well as of color when the object shifts from one place to the other in the space. The three dimensionality of the RVSI is proved by giving a hidden illumination within a space and by asking a subject to judge the lightness or color of a test patch placed in the area of the hidden illumination. In spite of the additional light on the test patch the subject did not recognize that the light was added but simply felt that the surface was made of a higher lightness or colored by transferring the light into an increase of the reflectance factor of the test patch. The results can be interpreted if we assume that a same RVSI exists throughout the entire space including the area of the hidden illumination.

Key words : illumination, lightness, apparent lightness, color constancy, color mode