In 1964 Edwin H. Land (ref. 4) formulated the Retinex theory, the first attempt to simulate and explain how the human visual system perceives color. His theory and an extension, the ``reset Retinex'' (ref. 5) were further formalized by Land and McCann in 1971. Several Retinex algorithms have been developed ever since. These color constancy algorithms modify the RGB values at each pixel to give an estimate of the physical color independent of the shading.

The Retinex original method was complex and imprecise. Indeed, this algorithm computes at each pixel an average of a very large and unspecified set of paths on the image. For this reason, Retinex has received several interpretations and implementations which, among other aims, attempt to tune down its excessive complexity