Reality and Perception in Stereo Vision - Technological Applications

In stereo vision, eyes capture two different views of a three-dimensional object. Retinal images are fused in the brain in a way that their disparities (or parallaxes) are transformed into depth perception, yielding a three-dimensional representation of the object in the observer’s mind. The process of transforming parallax into depth perception is not entirely understood. The main question refers to the quantitative connection between these two variables, which creates a significant difference between real object and perceived image, that is, between reality and perception. In general, the theme of depth perception has been approached from different points of view. In the first place, there is what could be called the geometric approach, because its methodology deals with relationships used in geometric optics for generating images. On this basis, several formulations were proposed for determining the vertical exaggeration perceived when aerial photographs are viewed stereoscopically (Aschenbrenner, 1952; Collins, 1981; Stone, 1951; Goodale, 1953; La Prade, 1972; 1973; 1978; Miller, 1960; Raasveldt, 1956; Yacoumelos, 1972; Yacoumelos,1973). At the end, none of these formulations has shown to be sufficiently reliable. Another approach to depth perception in stereo vision is the psychological one. Differently from the geometric approach, observations are performed under conditions of natural vision (Norman et al, 1996; Rucker, 1977, Wagner, 1985). This methodology has the value of permitting the observer to make direct estimations of depth perception. In this manner, there is no risk of confusing perceptual lengths with real lengths. However, psychological observations on depth perception, rather than being quantitative, remain at a qualitative level. A third approach to the study of depth perception is the physiological one. From that point, the attention centers on how the brain measures disparity form two retinal images. Qian, 1997 emphasizes the need of a better understanding of the brain function, and that any computational model must be based on real physiological data. On their turn, Backus, 2000; Backus, et al., 2001; and Chandrasekaran, et al., 2007 recognize that neural encoding of depth continues to be a mysterious subject. However, Mars, 1982, supports the belief that physiological details are not important for understanding visual perception, under certain mathematical assumptions. Consequently, he believes that physiological details do not become necessary for understanding the visual perception process.