Mitsuo IKEDA, Rumi YAMAUCHI and Hiroyuki SHINODA

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

(Received December 16, 2002; Accepted May 30, 2003; Revised May 7, 2003)

The retinal image of the outside world is two dimensional and the brain automatically transfers the 2D image to 3D space in order that a human can recognize the world correctly. A printed black and white picture of a grating or a cube was presented to subjects through a viewing box to exclude other objects than the pattern so that the brain was provided with only the information about the pattern and recognized a 3D space for the pattern efficiently. Once a space recognition was achieved there was constructed a recognized visual space of illumination (RVSI) which controlled the apparent lightness of gray patches drawn in the picture. In the grating experiment the apparent lightness of a gray stimulus drawn as if it were located on this side of the white stripes, was shown to become lower than that of a gray reference stimulus drawn behind the white stripes with black background when both stimuli had the same lightness. Similarly, in the cube experiment the apparent lightness of a gray stimulus drawn way behind the white cube was shown to become lower than that of a gray reference stimulus drawn over black stripes that lay on the cube. The amount of these space recognition effects on apparent lightness was about 0.5 in Munsell Value when measured by brightness matching between the test and the reference stimulus.

Key words: lightness, apparent lightness, space recognition, 3D, recognized visual space of illumination, brightness, illumination