Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site hou2e.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxl!houxm!hou2e!mike From: mike@hou2e.UUCP (M.LUKACS) Newsgroups: net.physics Subject: Re: color vision: not a fourier transform... Message-ID: <255@hou2e.UUCP> Date: Wed, 22-Aug-84 11:37:45 EDT Article-I.D.: hou2e.255 Posted: Wed Aug 22 11:37:45 1984 Date-Received: Thu, 23-Aug-84 00:47:56 EDT References: <188@mhuxm.UUCP>, <698@opus.UUCP> Organization: Bell Labs, Holmdel NJ Lines: 33 <........> Although the physical basis of normal human color perception consists of three overlaping sensitivity curves corresponding roughly to the "red", "green", and "blue" areas of the visual spectrum, the psychophysical color sense is much more complex and depends on a lot of post-processing, both automatic and cognitive (relying on memory and expectation). Early experiments by Land (the founder of Polaroid corp. originally Polaroid-Land) showed that under some conditions of intensity and composition most people could see a full color image projected in only two primaries. Later experiments at Bell Labs by C.B.Rubinstein, D.E.Pearson, and myself (~1969->1972) which removed any memory cues by using randomly generated quilts of color patches, proved that normal human observers would perceive near perfect renditions of color (all colors being present and identifiable) from images projected by red and white primaries only. The mechanism which causes this is the adaptation of vision to the average color content of a scene. This same mechanism can be seen operating when you look at a scene under different illuminations such as flourescent and incandescent lights or bright sun at noon vs. late afternoon sun vs. blue sky shade. We tend to see almost the same colors in all these situations (excepting pathologic pigments and/or lightings, which tend to have emitted or reflected spectrums with most of the energy concentrated in a few narrow frequency bands), but any photographer will tell you that the senes do not look at all similar to film or other nonadaptive media. Modern color television cameras have circuitry to mimic this effect of the human visual system, the camera operator must push a button to "white balance" the camera while looking at a portion of the scene that looks neutral in color to the operator. Michael E. Lukacs Room 2C-426 Bell Communications Research Holmdel, N. J. 07733 houxm!houxe!mike