Color Constancy Theory

The human eye is an amazing organ. It interprets thousands of complex signals within seconds, providing people with a visual sense of their surroundings. Color is a vital factor in sight. It plays an important role in safety and orientation. The color constancy theory helps scientists understand how the eye sees color under different lighting conditions.

History

• The topic of color perception has fascinated humans for centuries. Sir Isaac Newton was the first scientist to understand that light produces color. Later scientists and philosophers developed an interest in color perception. The German philosopher Johann Goethe wrote a treatise in 1810 advancing his own theory of colors, and refuting Newton. Scientists in the 19th and 20th centuries performed a variety of experiments on animals to test if they could see in color.

Human Color Perception

• Human sight involves a few factors: light, objects and cells in the eye called rods and cones. Light is reflected off objects and then enters the eye. The reflected light has a fixed percentage of energy at each wavelength. Cone cells in the eye's retina are responsible for processing color, and they send signals to the brain which tell it what color an object is. Therefore, in daylight, the sky will look blue and the grass will look green.

Theory

• Physicist and inventor Edwin Land postulated the retinex theory in 1971, which describes how the human eye processes color in a world with inconstant lighting. The word "retinex" combines two words: retina and cortex. The cortex is part of the human brain which is, among other things, responsible for perception. Land theorized that even if lighting conditions change, the retina and cortex will cooperate to ensure that the image of a specific object will not become unrecognizable, and will maintain a similar color to the observer.

Psychological Importance

• Color constancy is not only important for the study of optics; it is an important psychological precept as well. Humans would be highly perplexed if the color of an object changed every time the light reflecting off it changed. The world would be a highly uncertain place if humans could not perceive a constant color in different lighting conditions. Constancy is an important principle for people. Humans rely on constancy to recognize not only color, but also other people and direction.

Image Reproduction and Color Constancy

• The color constancy theory is applicable to image reproduction as well. A person's sense of color constancy will allow him to filter out the differences in lighting when viewing a picture. However, computers and cameras must be specially programmed and calibrated in order to produce an image which appears normal to humans. Scientists and researchers are working on algorithms to correct lighting differences in image reproductions.