Color constancy

There is an interesting phenomenon which occurs when an artist uses a limited color palette: the eye tends to compensate by seeing any gray or neutral color as the color which is missing from the color wheel. For example, in a limited palette consisting of red, yellow, black, and white, a mixture of yellow and black will appear as a variety of green, a mixture of red and black will appear as a variety of purple, and pure gray will appear bluish.[9] The trichromatic theory discussed above is strictly true when the visual system is in a fixed state of adaptation. In reality, the visual system is constantly adapting to changes in the environment and compares the various colors in a scene to reduce the effects of the illumination. If a scene is illuminated with one light, and then with another, as long as the difference between the light sources stays within a reasonable range, the colors in the scene appear relatively constant to us. This was studied by Edwin Land in the 1970s and led to his retinex theory of color constancy. It should be noted, that both phenomena described above are readily explained and mathematical modeled with modern theories of chromatic adaptation and color appearance (e.g. CIECAM02, iCAM).[10] There is no need to dismiss the trichromatic theory of vision, but rather it must be enhanced with an understanding of how the visual system adapts (adjusts) to changes in the viewing environment. Color constancy is an example of subjective constancy and a feature of the human color perception system which ensures that the perceived color of objects remains relatively constant under varying illumination conditions. A green apple for instance looks green to us at midday, when the main illumination is white sunlight, and also at sunset, when the main illumination is red. This helps us identify objects. Edwin Herbert Land, ForMemRS,[2] FRPS, Hon.MRI (May 7, 1909 Ц March 1, 1991) was an American scientist and inventor, best known as the co-founder of the Polaroid Cor

oration. Among other things, he invented inexpensive filters for polarizing light, a practical system of in-camera instant photography, and his retinex theory of color vision. His Polaroid instant camera, which went on sale in late 1948, made it possible for a picture to be taken and developed in 60 seconds or less. Edwin was born in Bridgeport, Connecticut to Harry and Helen Land of English Jewish descent. His father owned a scrap metal yard. He attended the Norwich Free Academy at Norwich, Connecticut, a semi-private high school, and graduated in the class of 1927. The library there was posthumously named for him, having been funded by grants from his family. He studied chemistry at Harvard University. After his freshman year, he left Harvard for New York City. In New York City, he invented the first inexpensive filters capable of polarizing light, Polaroid film. Because he was not associated with an educational institution, he lacked the tools of a proper laboratory, making this a difficult endeavor. Instead, he would sneak into a laboratory at Columbia University late at night to use their equipment.[3] He also availed himself of the New York City Public Library to scour the scientific literature for prior work on polarizing substances. His breakthrough came when he realized that instead of attempting to grow a large single crystal of a polarizing substance, he could manufacture a film with millions of micron-sized polarizing crystals that were coaxed into perfect alignment with each other. After developing a polarizing film, Edwin Land returned to Harvard University. However, he still did not finish his studies or receive a degree. Once Land could see the solution to a problem in his head, he lost all motivation to write it down or prove his vision to others.[4] Often his wife, at the prodding of his instructor, would extract from him the answers to homework problems. She would then write up the homework and hand it in so he could receive credit and not fail the course.