Reprinted from Nature, Vol. 350, No. 6317, pp. 379-380,4th April, 1991 0Macmillan Magazines Ltd., 199 1 OBITUARY phenomena, were by-products of the visual mechanism that gives us colour Edwin Herbert Land (1909-1991) constancy - our ability to recognize IN1957, Harvard University awarded an Polaroid Corporation in 1982. the permanent colours of objects honorary doctorate to a man who Much less known than his cameras, despite large changes in the spectral dropped out of its freshman physics class but probably of more significance, was composition of the illumination. In the of 1926. After leaving Harvard, he had Land's secret work on high-altitude opti- example given above, the illumination continued his education in the New York :a1 surveillance systems. In the 1950s, he will be regarded patches Public Library and had become one of the led the team that designed the high-resol- that reflect less 1 t (those great American scientific entrepreneurs, ution camera for the U2 spy plane - the illuminated mainly by the second trans- to be counted alongside Edison and Bell. forerunner of later systems mounted in parency) will be interpreted as greenish Such was Edwin Land, who died on 1 satellites. or bluish objects. March. For the last 35 years of his life, Land's Rather more slowly than Woolfson By 1932, Land had succeeded in align- main scientific obsession was colour vi- and Judd, Land himself realized the re- sion, a subject that has lationship between his two-colour dem- been a seductive and pas- onstrations and colour constancy, and sion-provoking mistress to during the next two decades he de- so many physicists. His veloped a second series of demonstra- writings and lectures at- tions, the 'Mondrian' demonstrations. tracted (thoroughly justi- These were grand (but increasingly la- fied) hostility from estab- boured) demonstrations of colour con- lished colour scientists, but stancy. Land always eschewed the term he was able to leave gener- 'colour constancy' and declined to re- ations of undergraduates late his demonstrations to a long-estab- with the notion that he had lished tradition in colour science. Yet refuted existing theory. Young himself wrote in 1807 ". ..when a It was in the late 1950s room is illuminated either by the yellow that he captured public light of a candle, or by the red light of a imagination with his two- fire, a sheet of writing paper still ap- colour demonstrations. A pears to retain its whiteness". And in black-and-white photo- fact Land's death coincides with the graph of a scene is taken bicentennial of the masterly paper by ¥throughsay, a red filter, Monge, in which that great mathemati- and a second is taken of the cian relates coloured shadows to colour same scene through a constancy and draws Land's conclusion green filter. A positive - that we respond not to the absolute transparency is prepared properties of the stimuli that strike our from each of the two nega- retinae but to their ratios. tives. The first trans- It must nevertheless be said that parency is then projected Land's attentions revived a quiescent on a screen through a red field. And his theory of colour constanc Double take - Land demonstrating his instant photographs filter; the second is pro- was important. The idea was that eac in 1947. jected in register, but with of the three cone systems extracts the ing submicroscopic crystals of iodo- unfiltered white light. We might expect to spatial pattern of light and dark as seen quinine sulphate and embedding them in s, pinks and whites - by those cones, scaling each local signal a sheet of plastic, so as to yield large reds where the first transparency was according to the total range ofillumina- sheets of artificial polarizer. With his light and the second dark, pinks where tions that it finds over a larger region. Harvard physics instructor, George the transparencies had similar density, Later, a comparison is made of the three Wheelwright, he set up the Land-Wheel- and whites where the second was the separate lightness signals for a given wright Laboratories in 1932; and he lighter. In fact, the image on the screen ex- local area, and this comparison gives established the Polaroid Corporation in hibits a much richer gamut of colours, the colour of the corresponding surface. 1937. Polaroid filters, for visible and which includes blues and greens. This 'retinex' theory was an early infrared light, were soon being used in The two-colour demonstration shows example of a computational model of cameras and sunglasses, and in war- that there is no fixed relation between the how the brain might accomplish a par- time rangefinders and night-adaptation spectral composition of light and the hue ticular task. goggles. that we perceive at a local point in the In public manner, Land was at once Land's first instant camera, yielding a scene. Rather, we judge colours by the shy and imperious. Like many in his po- picture in 60 seconds, was demonstrated company they keep. Land took his find- sition, he gained the reputation of a re- to the Optical Society of America in 1947. ing to contradict what he held to be cluse. In 1980 he saw the potential of a By Christmas of 1948, it was on sale to the the classical colour theory of Young and vacant lot beside the Charles River, and public. An instant colour camera was of Helmholtz. built there his Rowland Institute. It was marketed in 1963. It was a classic case of The less insightful of his critics com- a cross between an art gallery and the giving away the razor and making the plained that his effects, apart from being private laboratory of a nineteenth-cen- money on the blades. Land and his com- rediscoveries, were all a matter of colour tury gentleman scientist - with per- pany became very rich. But an instant contrast. Those who thought more deep- haps just a touch of Hearst Castle. movie system, placed on the market ly, such as M. Woolfson (IBM Journal 3, J. D. Mollon just as domestic video systems were be- 313,1959) and D. Judd (J. opt. Soc. Am. J. D. Mollon is in the Department of coming available, proved commercially 50, 254; 1960) grasped that the Land Experimental Psychology, University of disastrous; and Land retired from the effects, like several other contrast Cambridge, Cambridge CB2 3EB, UK. .