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Color photography - Invented by James Clerk Maxwell

James Clerk Maxwell-Color photography
: James Clerk Maxwell (Know about James Clerk Maxwell)
: 1861
: United Kingdom
: Physics

About Invention

Color photography is photography that uses media capable of reproducing colors. By contrast, black-and-white (monochrome) photography records only a single channel of luminance (brightness) and uses media capable only of showing shades of gray.

In color photography, electronic sensors or light-sensitive chemicals record color information at the time of exposure. This is usually done by analyzing the spectrum of colors into three channels of information, one dominated by red, another by green and the third by blue, in imitation of the way the normal human eye senses color. The recorded information is then used to reproduce the original colors by mixing various proportions of red, green and blue light (RGB color, used by video displays, digital projectors and some historical photographic processes), or by using dyes or pigments to remove various proportions of the red, green and blue which are present in white light (CMY color, used for prints on paper and transparencies on film).

Monochrome images which have been "colorized" by tinting selected areas by hand or mechanically or with the aid of a computer are "colored photographs," not "color photographs." Their colors are not dependent on the actual colors of the objects photographed and may be very inaccurate or completely imaginary.

Color photography is the dominant form of photography since 1970's with monochrome photography mostly relegated to niche markets such as art photography.


Early experiments

Color photography was attempted beginning in the 1840s. Early experiments were directed at finding a "chameleon substance" which would assume the color of the light falling on it. Some encouraging early results, typically obtained by projecting a solar spectrum directly onto the sensitive surface, seemed to promise eventual success, but the comparatively dim image formed in a camera required exposures lasting for hours or even days. The quality and range of the color was sometimes severely limited, as in the chemically complicated "Hillotype" process invented by American Daguerreotypist Levi Hill around 1850. Other experimenters, such as Edmond Becquerel, achieved better results but could find no way to prevent the colors from quickly fading when the images were exposed to light for viewing. Over the following several decades, renewed experiments along these lines periodically raised hopes and then dashed them, yielding nothing of practical value.

Three-color processes

The three-color method, which is the foundation of virtually all practical color processes whether chemical or electronic, was first suggested in an 1855 paper on color vision by Scottish physicist James Clerk Maxwell.

It is based on the Young-Helmholtz theory that the normal human eye sees color because its inner surface is covered with millions of intermingled cone cells of three types: In theory one type is most sensitive to the end of the spectrum we call "red", one more sensitive to the middle or "green" region, and one which is most strongly stimulated by "blue". The named colors are somewhat arbitrary divisions imposed on the continuous spectrum of visible light, and the theory is not an entirely accurate description of cone sensitivity. But the simple description of these three colors coincides enough with the sensations experienced by the eye that when these three colors are used the three cones types are adequately and unequally stimulated to form the illusion of various intermediate wavelengths of light.

In his studies of color vision, Maxwell showed, by using a rotating disk with which he could alter the proportions, that any visible hue or gray tone could be made by mixing only three pure colors of light – red, green and blue – in proportions that would stimulate the three types of cells to the same degrees under particular lighting conditions.To emphasize that each type of cell by itself did not actually see color but was simply more or less stimulated, he drew an analogy to black-and-white photography: if three colorless photographs of the same scene were taken through red, green and blue filters, and transparencies ("slides") made from them were projected through the same filters and superimposed on a screen, the result would be an image reproducing not only red, green and blue, but all of the colors in the original scene.

The first color photograph made according to Maxwell's prescription, a set of three monochrome "color separations", was taken by Thomas Sutton in 1861 for use in illustrating a lecture on color by Maxwell, where it was shown in color by the triple projection method. The test subject was a bow made of ribbon with stripes of various colors, apparently including red and green. During the lecture, which was about physics and physiology, not photography, Maxwell commented on the inadequacy of the results and the need for a photographic material more sensitive to red and green light. A century later, historians were mystified by the reproduction of any red at all, because the photographic process used by Sutton was for all practical purposes totally insensitive to red light and only marginally sensitive to green. In 1961, researchers found that many red dyes also reflect ultraviolet light, coincidentally transmitted by Sutton’s red filter, and surmised that the three images were probably due to ultra-violet, blue-green and blue wavelengths, rather than to red, green and blue.

Maxwell's 1855 suggestion and this tentative 1861 demonstration appear to have been quickly and completely forgotten until being brought to light again in the 1890s. In the intervening decades, the basic concept was independently re-invented by several people.

Color photography leaves the laboratory

Prior to the late 1890s, color photography was strictly the domain of a very few intrepid experimenters willing to build their own equipment, do their own color-sensitizing of photographic emulsions, make and test their own color filters and otherwise devote a large amount of time and effort to their pursuits. There were many opportunities for something to go wrong during the series of operations required and problem-free results were rare. Most photographers still regarded the whole idea of color photography as a pipe dream, something only madmen and swindlers would claim to have accomplished.

In 1898, however, it was possible for anyone with the price in hand to buy the required equipment and supplies ready-made. Two adequately red-sensitive photographic plates were already on the market, and two very different systems of color photography with which to use them, tantalizingly described in photographic magazines for several years past, were finally available to the public.

The most extensive and expensive of the two was the "Kromskop" (pronounced "chrome-scope") system developed by Frederic Eugene Ives. This was a straightforward additive system and its essential elements had been described by James Clerk Maxwell, Louis Ducos du Hauron and Charles Cros much earlier, but Ives invested years of careful work and ingenuity in refining the methods and materials to optimize color quality, in overcoming problems inherent in the optical systems involved, and in simplifying the apparatus to bring down the cost of producing it commercially. The color images, dubbed "Kromograms," were in the form of sets of three black-and-white transparencies on glass, mounted onto special cloth-tape-hinged triple cardboard frames. To see a Kromogram in color it had to be inserted into a "Kromskop" (generic name "chromoscope" or "photochromoscope"), a viewing device which used an arrangement of colored glass filters to illuminate each slide with the correct color of light and transparent reflectors to visually combine them into a single full-color image. The most popular model was stereoscopic. By looking through its pair of lenses, an image in full natural color and 3-D was seen, a startling novelty in the late Victorian age.

The results won near-universal praise for excellence and realism. At demonstrations, Ives sometimes placed a viewer displaying a still-life subject next to the actual objects photographed, inviting direct comparison. A Kromskop triple "lantern" could be used to project the three images, mounted in a special metal or wooden frame for this purpose, through filters as Maxwell had done in 1861. Prepared Kromograms of still-life subjects, landscapes, famous buildings and works of art were sold and these were the Kromskop viewer's usual fodder, but a "multiple back" camera attachment and a set of three specially adjusted color filters could be bought by "Kromskopists" wishing to make their own Kromograms.

Kromskops and ready-made Kromograms were bought by educational institutions for their value in teaching about color and color vision, and by individuals who were in a position to pay a substantial sum for an intriguing optical toy. A few people did, indeed, make their own Kromograms. Unfortunately for Ives, this was not enough to sustain the businesses which had been set up to exploit the system and they soon failed, but the viewers, projectors, Kromograms and several varieties of Kromskop cameras and camera attachments continued to be available through the Scientific Shop in Chicago as late as 1907.


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