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Definition
Retinex theory is a computational model for human color constancy. It defines a mechanism for computing lightness values from an image. Retinex theory proposes that the lightness values for each class of photoreceptors are derived independently and that this triplet of values correlates with perceived reflectance.
Background
The human visual system is remarkable in its ability to deal with varying illumination. Throughout the day, the visual system encounters both artificial and natural illumination, yet the appearance of the world seems stable. For example, a piece of white paper on a desk does not appear to change color when taken outside.
But anyone who has used a camera knows that the world is not as simple as it appears. Sometimes photographs captured outdoors have a blue color cast, while photographs captured indoors appear yellow. These color shifts are due to the different sources of...