gazzan optical illusions英文电子书.pdf

Adelson, E.H. Lightness Perception and Lightness Illusions. In The New Cognitive Neurosciences, 2nd ed., M. Gazzaniga, ed. Cambridge, MA: MIT Press, pp. 339-351, (2000). 24 Lightness Perception and Lightness Illusions EDWARD H. ADELSON ABSTRACT: A gray surface in sunlight may have much higher shade of gray. However, the square in the dark surround luminance than it has in the shade, but it still looks gray. To achieve appears lighter than the square in the light surround. the task of “lightness constancy,” the visual system must discount Illusions like these are sometimes viewed as quirky failures the illumination and other viewing conditions and estimate the of perception, but they help reveal the inner workings of a reflectance. Many different physical situations, such as shadows, fil- system that functions remarkably well. Here we will consid- ters, or haze, can be combined to form a single, simple mapping er how lightness illusions can inform us about lightness per- from luminance to reflectance. The net effect of the viewing condi- ception. tions, including additive and multiplicative effects, may be termed an “atmosphere.” An “atmospheric transfer function” maps reflectance into luminance. To correctly estimate lightness, a visual Levels of processing system must determine a “lightness transfer function” that performs the inverse. Human lightness computation is imperfect, but per- The visual system processes information at many levels of forms well in most natural situations. Lightness illusions can reveal sophistication. At the retina, there is low-level v