retinex

Retinex is a theory and a set of algorithms developed to explain and model human color perception and visual adaptation. Proposed by Edwin Land, the creator of Polaroid, Retinex attempts to describe how the brain processes visual information to perceive the color and brightness of objects independently of the illumination conditions. The term "Retinex" is a portmanteau of "retina" and "cortex," suggesting that both retinal processing and cortical interpretation are involved in this phenomenon.

The core idea behind Retinex is that the perceived color of an object is determined by the ratios of the light reflected from that object across different wavelengths, rather than by the absolute amount of light. This allows the visual system to maintain a consistent perception of color and lightness even when the overall illumination changes, such as moving from bright sunlight to a dimly lit room. Essentially, the brain analyzes the relative contributions of different light sources and surfaces to determine the intrinsic reflectance properties of an object.

Various Retinex algorithms have been developed to computationally simulate this process. These algorithms typically involve decomposing an image into components representing illumination and reflectance. By estimating and removing the illumination component, the intrinsic reflectance of the surfaces can be recovered, leading to a more stable and natural-looking image that better represents how a human would perceive it under varying lighting. Retinex algorithms have found applications in image processing, computer vision, and computational photography, particularly in tasks like color constancy, dynamic range compression, and image enhancement.