How the human visual system determines the lightness of a surface, that is, its whiteness, blackness, or grayness, remains, like vision in general, a mystery. In fact, we have not been able to create a machine that can determine, through an artificial vision system, whether an object is white, black, or gray. Although the photoreceptors in the eye are driven by light, the light reflected by a surface does not reveal its shade of gray. Depending upon the level of illumination, a surface of any shade of gray can reflect any amount of light. This book ties together over thirty years of the author ... More

How the human visual system determines the lightness of a surface, that is, its whiteness, blackness, or grayness, remains, like vision in general, a mystery. In fact, we have not been able to create a machine that can determine, through an artificial vision system, whether an object is white, black, or gray. Although the photoreceptors in the eye are driven by light, the light reflected by a surface does not reveal its shade of gray. Depending upon the level of illumination, a surface of any shade of gray can reflect any amount of light. This book ties together over thirty years of the author's own research on lightness, and presents an historical review of empirical work on lightness, covering the past 150 years of research on images ranging from the simple to the complex. The book also describes and analyzes the many theories of lightness — including the author's own — showing what each can and cannot explain. The book highlights the forgotten work conducted in the first third of the 20th century, describing several crucial experiments and examining the nearly unknown work of the Hungarian gestalt theorist, Lajos Kardos. The book's review also includes a survey of the pattern of lightness errors made by humans, many of which result in delightful illusions. It argues that because these errors are not random, but systematic, they are the signature of our visual software, and so provide a powerful tool that can reveal how lightness is computed. Based on this argument and the concepts of anchoring, grouping, and frames of reference, the book presents a new theoretical framework that explains an unprecedented array of lightness errors.