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Physics & Physiology of Color

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Edwin H. Land

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Edwin Land's
Interesting Accident

A 2-Color System
 

Edwin Land was an inventor and self-made practitioner of science.  He applied polarization to sunglasses and automobile headlights.  He invented instant black and white photography—Polaroid film, and the camera that used it.

In the nineteen-fifties, he set about developing instant color photography.  He began by studying the basics of color reproduction, and early in his experiments repeated J. C. Maxwell's classic three-color photography demonstration, but did it with modern films and materials.  

One day, as he was dismantling his system of three projectors, he had turned off the blue-filtered projector, and removed the green filter from its projector.  That left the red-record image on the screen, projected with red light, and  the green-record image, projected with white light.   

His assistant asked why all the colors in the original image were still visible.  Why indeed?!?!  The image should have contained shades of black, white and red.  But both Land and his assistant could see blue, green and yellow as well.  When they darkened the image from the unfiltered projector, the colors became richer.  

The two transparencies that were in use at the time of the accident had been made using sharp-cutting filters, one recording only the red region of the spectrum and the other recording only the green region.  Neither transparency had recorded any blue or violet light at all.  Yet the projected image revealed blue color, right where it belonged in the image.

Land never found a practical way to apply the phenomenon to instant photography, and he ultimately developed Polaroid color film using a conventional three-color system.

But the interesting accident raised profound questions about the physics and physiology of color vision, and set Land off on extensive investigations of 2-color photography.  He continued to record his images using only red and green light, but experimented widely with projection colors.

He engineered a method of illuminating images with very narrow bands of the spectrum, and investigated the possibilities of creating full-color images with a variety of color environments.  He was ultimately able to create full-color images with only light of 579 nanometers and 599 nanometers wavelength.  We normally perceive those two specimens of light as being yellow, and almost identical in color, but two-color images viewed with those colors of light can produce the perception of reds, greens and blues.

The two-color images lack a full range of values and chromas, but they do reproduce all hues.  They are reminiscent of the written descriptions of J. C. Maxwell's first three-color images in 1861.  The Muser's article on Maxwell's experiments explains that Maxwell did not have the materials necessary to accomplish what he thought he was doing in his experiments.  Where Land's nineteen-fifties images didn't record any blue light, Maxwell's eighteen-sixties images couldn't have recorded any red or green light.  Yet both obtained satisfactory color reproduction.  It seems possible that their results will one day have a common explanation.

Land's early experiments are reported in a 1959 article in Scientific American.   He abandoned the work for a number of years, and returned to it in the late sixties.  In his later work, he developed what he called a Retinex Theory of Color Vision.  That research is also reported in Scientific American articles.  In The Muser's opinion, the later work lacks the simple elegance of Land's earlier inquiries.  It doesn't seem to adequately answer the questions raised in the fifties experiments.  And it doesn't tie together the loose ends of the past two centuries of color vision investigations.

We still have more questions than answers.

Land, E.H., Scientific American, May 1959
Land, E.H., Scientific American, Dec. 1977, p. 108++
Thanks to Larry Elie for these citations, and a couple of corrections.

© J. C. Adamson, 2001