The Retinex Theory of Color Vision

In their experiments, Land and McCann identified edges as being important in the determination of the reflectances of an object (Land and McCann 1971). They demonstrated this using two sheets of paper. One reflected 40% of the incident light and the other reflected 80% of the incident light. Two fluorescent tubes were used to illuminate the two sheets of papers. One was placed in front of the two papers and the other one was placed on the side of it. The second tube was positioned such that the amount of reflected light was 

Color Constancy M. Ebner 2007 John Wiley Sons, Ltd 

the ratio of luminances between the first two rectangles along the path is calculated. We calculate = 9.98. When the path crosses the boundary to another rectangle, the ratio is multiplied with the ratio of luminances between the current and the next rectangle 

Both ratios can be multiplied to obtain the ratio between the first and the third rectangle, = nil = 1-02. We can continue this process until we have reached the last rectangle. We obtain 

Obviously, this ratio is equivalent to the ratio between the first and the last rectangle along the path. Since all the intermediate luminances cancel, the resulting ratio does not depend on the actual path taken. It only depends on the position of the starting point and on the position of the ending point. 

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Land and McCann (1971) came to the conclusion that color perception involves structures of the retina as well as the visual cortex. On the basis of these experiments, Land and McCann developed a computational theory of color constancy, the retinex theory. Land later developed additional versions of his retinex theory. The retinex theory of color vision is discussed in detail in Chapter 7. 

The computed output color is independent of the illuminant. The retinex theory of color vision was also analyzed in depth by Brainard and Wandell (1992). Brainard and Wandell experimented with color Mondrians consisting of nine colored patches. They found that the retinex algorithm does not correctly predict color appearance when the composition of the Mondrian is varied. The results of Brainard and Wandell could be due to the use of infinite path lengths for the retinex algorithm. The effect of the path length on the retinex algorithm is discussed by (Ciurea and Funt 2004). 

Brainard DH and Wandell BA 1992 Analysis of the retinex theory of color vision In Color (eds. Healey GE, Shafer SA and Wolff LB), pp. 208-218. Jones and Bartlett Publishers, Boston. 

Land EH 1986a An alternative technique for the computation of the designator in the retinex theory of color vision. Proceedings of the National Academy of Sciences of the United States of America 83, 3078-3080. 

Figure 2.20 The transformation performed by the color opponency mechanism may be a simple rotation of the coordinate system. In this case, the mechanism for color constancy may operate on the rotated coordinates. (Reprinted from Vision Res., Vol. 26, No. 1, Edwin H. Land, Recent advances in retinex theory, pp. 7-21, Copyright 1986, with permission from Elsevier.)...

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