Theory That Explains Color Constancy
The human eye is equipped to function under a variety of different circumstances. A green building appears green both in the morning and also when the sun begins to set. Changes in lighting may, or may not affect the eyes ability to identify objects and colors. The theory of color constancy describes how this works.
Identification
Color constancy refers to the human eye's ability to discern colors under bright lighting, as well as under dimmed lighting. Retinex theory, developed by a physicist named Edwin H. Land in 1971, provides an explanation as to how the eyes are able to identify color in both light and dark conditions. This ability is what enables a person to identify objects. This process is called subjective constancy in which a person's perception of an object remains constant under changing conditions. The Retinex theory attributes this ability to specialized double-opponent cells.
Subjective Constancy
Subjective constancy is a physiological process in which certain neurons in the brain's primary visual cortex record and compile the cone activity in the eyes. Under the Retinex theory, these neurons are the double-opponent cells. Double-opponent cells calculate color ratios and spatial elements. Color ratios refer to the types of wavelengths being reflected by an object. Spatial elements make up the distances, or transitions that take place between one wavelength and another. In order for the human to make these calculations, the light source must contain certain identifiable wavelengths.
Visible Spectrum
The theory of color constancy relies on the "visible light window" portion of the electromagnetic spectrum The electromagnetic spectrum is made up of all the light wavelengths that enter the Earth's atmosphere. The visible light spectrum, or window is contains the wavelengths that the human eye can see. This spectrum is made up of primary and secondary colors. The scientific primary colors are red, blue and green, while the secondary colors are yellow, purple and orange. (These differ from artistic primary and secondary colors.) Other colors within the visible spectrum are made up of mixtures of the primary and secondary wavelengths.
Rods and Cones
The human eye contains specialized cells called rods and cones. These cells contain photopigments that are sensitive to certain wavelengths, or colors. Three different types of cone cells are attuned to red, green and blue wavelengths. Each cone type can only pick up its assigned wavelength, be it red, green or blue. Rod cells are designed to be light-sensitive, and contribute to the eyes' ability to discern color under darkened conditions. The specialized cells identified in the Retinex theory of color constancy work in conjunction with rod and cones cells to discern color differences under various lighting conditions.
Phototransduction
Phototransduction is another explanation for how color constancy works in the human eye. Phototransduction focuses on the interactions that takes place between individual rod and cone cells with incoming wavelengths of light. As the rod cells are designed to amplify incoming wavelengths in darkened conditions, these cells are highly sensitized to any presence of light in dark surroundings. The cone cells, in turn, carry out their usual function in picking up red, blue or green wavelengths, however they are only activated by their respective color waves.
Tags: Retinex theory, cone cells, primary secondary, secondary colors, spectrum made, theory color