In 1894 John Joly, a Dublin physicist, patented the first linescreen process for additive color photographs, based on Louis Ducos du Hauron’s concept. In this process, a glass screen with transparent ruled lines of red, green, and blue, about two hundred lines per inch, was placed against the emulsion of an orthochromatic (not sensitive to red light) plate. The exposure was made and the screen removed. The plate was processed and contact printed on another plate to make a positive black-andwhite transparency which was placed in exact register with the same screen used to make the exposure. The final result was a limited-color photographic transparency that was viewed by transmitted light. Introduced in 1896 as the Joly Color process, this method enjoyed only a brief success. It was expensive and the available emulsions still were not sensitive to the full range of the spectrum, thus the final image was not able to achieve the look of “natural” color. However, Joly’s work indicated that the additive screen process had the potential to become a commercially viable way of making color photographs. [1|2|8|1455]Additional examples:
 
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In Lyons, France, Auguste and Louis Lumière, the inventors of the first practical motion picture projector, patented a major breakthrough in the making of color photographs in 1904. The Autochrome Lumière was the first commercially viable and extensively used color photographic process. Introduced to the market in 1907, it remained in production until 1935. Autochrome was a reversal process, which produced one unique image—a positive transparency on a glass support that was viewed by projection or through a transmitted light source. [1|2|9|1456]Additional examples:
 
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An Autochrome plate was produced as follows: (1) a glass support was covered with an initial layer of varnish that remained tacky; (2) the color screen layer, composed of potato starch grains dyed orange-red, green, and violet-blue, was dusted onto the sticky varnish; (3) a fine carbon black powder was used to fill remaining gaps between the grains, and the layers were then pressed flat in a rolling press; (4) a second varnish was applied to protect the starch grains from moisture; (5) a photosensitive layer of silver gelatin emulsion was then applied ; panchromatic emulsion, which greatly extended the accuracy of recording the full range of the visible spectrum, became the emulsion of choice once it became commercially available in 1906; (6) after exposure and processing, the manufacturer recommended a final coat of varnish to further protect the plate before a cover glass was applied to preserve the entire color image. [1|2|9|1457]Additional examples:
 
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To maintain a proper color balance, a deep yellow filter was placed in front of the camera lens. The exposure was made with the plate’s filter layer pointed toward the lens, so that the dyed potato starch acted as tiny filters. After development, the plate was re-exposed to light, and finally redeveloped to form a positive transparency made up of tiny dots of the primary colors. The Autochrome was a pioneering method of utilizing the principles articulated by Ducos du Hauron and Charles Cros in which the eye mixed the colors, in a fashion much like George Seurat’s pointillist painting Sunday Afternoon on the Island of La Grande Jatte (1884 – 1886), to make a color-positive image. Alfred Stieglitz sang its praises in Camera Work, Number 20, October 1907: “Color photography is an accomplished fact. The seemingly everlasting question whether color would ever be within the reach of the photographer has been definitely answered … The possibilities of the process seem to be unlimited … In short, soon the world will be color-mad, and Lumière will be responsible.” [1|2|9|1458]

Used from 1907 to 1935, Autochrome did have its limitations. Since the light had to travel through the potato starch grains and the yellow filter on the front of the lens, exposure times were much longer than with the black-and-white films of the day. In the additive processes, it was not uncommon for 75 percent or more of the light to be absorbed by this combination of filters before reaching the emulsion. Suggested starting exposure time was between 1/5 of a second and 1 second at f/4 in direct sunlight at midday in the summer and six times longer on a cloudy day, although over time there were many suggestions on how to increase its sensitivity. The randomly applied potato grains tended to bunch up, creating blobs of color. Also, Autochromes that were not lantern projected could be difficult to see and were sometimes placed in specially designed viewers called diascopes. When they were regularly marketed in New York (ca. 1910), a box of four 3 1/4 × 4-inch plates cost $1.20 and a box of 7 × 14-inch plates sold for $7.50, making them pricey for an average working person. [1|2|9|1459]Additional examples:
 
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The advantages of this process, however, were numerous. Autochromes could be used in any regular plate camera with the addition of a special yellow-orange filter; the image was made in one exposure, not in three; although pricey, the cost was not overly prohibitive; it gave serious amateurs much easier access to color; and while the colors were not accurate by today’s standards, they did produce a warm, soft, and inviting pastel image that people considered to be quite pleasing. [1|2|9|1460]Additional examples:
 
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World War I was the first major conflict to be covered by color photography. Autochromes became the basis for publications such as L’Histoire illustrée de la guerre de 1914. By the end of World War I, magazines such as National Geographic were using Autochromes to make color reproductions for the first time in their publications. Between 1914 and 1938, National Geographic published a reported 2,355 Autochromes, more than any other journal, thus taking a leadership role in bringing the “realism” of color photography into mass circulation. Autochrome was the first color process to get beyond the novelty stage and to become successful in the market place. It cracked a major aesthetic barrier because it was taken seriously for its picture-making potentialities. This enabled photographers to begin to explore the visual possibilities of making meaningful color photographs for ambitious projects such as Albert Kahn’s Archives of the Planet . Between 1909 and 1931, the French banker financed photographic teams who visited over 50 countries and amassed some 72,000 Autochrome plates that documented the diversity of the human condition in color, not just as ethnography or reportage but also for the purpose of inspiring education and universal peace. ¹ [1|2|9|1461]Additional examples:
 
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Other additive screen processes followed on the heels of Autochrome. In 1906 Clare L. Finlay of England patented a process that was introduced in 1908 as the Thames Colour Screen. Made up in a precise checkerboard fashion of red, green, and blue elements, rather than the random mosaic pattern used in Autochrome, this separate screen could be used with any type of panchromatic film or plate to make a color photograph. The Thames Colour Plate, which combined an integral screen with the emulsion to form a single plate, was released in 1909. Both of these processes were abandoned after World War I, but improved versions were marketed under the name of Finlay Colour in 1929 and 1931. The Finlay Colour processes were to be the major rivals to Dufaycolor until the introduction of subtractive-process materials in the mid-1930s. [1|2|10|1462]Additional examples:
 
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In 1912 G.S. Whitfield also obtained a patent for screenplates that were marketed by the Paget Dry Plate Company. Renamed Duplex in 1920, the process was discontinued few years later. [1|2|10|1463]

From about 1909 to 1914, the French firm of Louis Dufay made the Dioptichrome Plate to compete with the Autochrome. Although withdrawn from production, the process later was improved and renamed Dufaycolor when it was introduced as a ciné film in 1932. Soon produced as both cut-sheet and roll film, thus making it simple to use, Dufaycolor gave wider public access to color photography. The process became popular, especially in the UK, because it was faster (more light sensitive) than Autochrome and did not require any additional optical device to form a viewable image. Also, some people preferred the structure of its screen, which was a mosaic of alternating blue-dye and green-dye squares that were crossed at right angles by a pattern of parallel red-dye lines. This design offered greater color accuracy and a faster emulsion; by the mid-1930s exposures of f/8 at 1/25 of a second on a sunny day were possible, but the projected image was subdued and flawed by the conspicuous mosaic pattern. Dufaycolor was marketed until the late 1940s. By this time, the quest for an easier-to-use process that would provide more realistic and natural colors brought about technical discoveries that would eventually make the additive screen processes commercially obsolete. However, various film-based versions of Autochrome, including Filmcolor (1931), Lumicolor (1933), and Atlicolor (1952), were made into the mid-1950s. [1|2|11|1464]

Between 1983 and 2002 Polaroid (see Diffusion-Transfer Process later in this chapter) marketed Polachrome, an instant 35mm color slide film that could be used in any 35mm camera, which was based on additive-color, line-screen, positive-transparency film similar to Joly Color. The film was inserted with an individual chemical pod into a small tabletop Polaroid AutoProcessor for processing. Although it was convenient, it never achieved widespread use due to issues of color accuracy and because the line-screen became highly visible when the image was projected or enlarged. [1|2|12|1465]

Today the additive method is occasionally employed in color printmaking. It is in limited use because additive enlarger systems are more complex and expensive. To make a full color print with the additive process, the enlarger is used to make three separate exposures, one through each of the three primary-colored filters. The blue filter is used first and controls the amount of blue in the print, next the green filter is used for the green content, and last is the red filter. Some people prefer this additive technique, also known as tricolor printing, because it is relatively easy to make adjustments in the filter pack, with each filter controlling its own color. [1|2|13|1466]

A major change in additive color printing is the use of digital enlargers in professional photography labs that continue to make chemical prints on silver halide paper (light-sensitive compounds in paper and film). Instead of the older bulb-based printers, this combination of chemical-based color printing and digital imaging relies on rapid bursts of laser light in three colors — red, green, and blue — to expose the photographic paper. The laser light is bounced off a rotating six-sided mirror that reflects the light dots onto the paper. As the mirror turns, it draws a line across the paper in light, making extremely sharp images. These digital enlargers have the additional advantage of high-speed scanners and the ability to work from a digital file, which allows each image to be analyzed by software that adjusts color, contrast, and exposure as needed. It also has facial recognition software for smoothing facial features so that not every skin pore is sharply apparent. Other systems, such as Durst Lambda and LightJet, use LED light printers instead of lasers. [1|2|14|1467]

The additive system is the ideal vehicle for color television since the set creates and then emits the light-forming picture. The cathode ray tube (CRT) in color television has three electron guns, each corresponding to one of the additive primaries. These guns stimulate red, green, or blue phosphors on the screen to create different combinations of the three primaries. This creates all the colors that form the images we see on the television set. Liquid crystal display (LCD) and plasma (a type of gas) flat-screen televisions use the same RGB concept to have pixels (picture element) form the color image. A typical 8-bit LCD or plasma television utilizes a 256 red × 256 green × 256 blue subpixel depth to deliver 16,777,216 color combinations. [1|2|15|1468]

Louis Ducos du Hauron not only proposed a method for making color photographs with the additive process in Les Couleurs en photographie , he also suggested a method for making color photographs using the subtractive process. [1|2|16|1469]

The subtractive process operates by removing certain colors from white light while allowing others to pass. The modern subtractive primaries (cyan, magenta, and yellow) are the complementary colors of the three additive primaries (red, green, and blue). When white light is passed through one of the subtractive-colored filters it transmits two of the primaries and absorbs (subtracts) the other. Individually, each subtractive filter transmits two-thirds of the spectrum while blocking one-third of it. For example, a magenta filter passes red and blue but blocks green. When two filters are superimposed, they subtract two primaries and transmit one. Magenta and yellow filters block green and blue, allowing red to pass. When all three subtractive primaries overlap in equal amounts, they block all the wavelengths and produce black. When mixed in varying proportions, they are capable of making almost any color. The advantages of the subtractive method over the additive process are twofold: It makes possible a full-color reproduction on paper and dispenses with the prior need for expensive and cumbersome viewing equipment. [1|2|16|1470]

When working with pigments – as in painting – instead of light, the colors are also formed subtractively. The different colors of pigments absorb certain wavelengths of light and reflect others back for us to see. However, there is a major distinction between the primary colors of pigment and those of light, as painters generally use red, blue, and yellow for their primary colors. These colors cannot be mixed from any other colors and in theory are used to make all other colors, with the assistance of black-and-white. For example, red and yellow make orange, red and blue make purple, and blue and yellow make green. Green, an additive primary, is not a primary color in paint because it must be made from two colors: blue and yellow. In practice, it is necessary to use secondary and intermediate colors when mixing other colors, such as green and violet, because artist’s pigment is not “pure color.” The wavelengths of its minor components are different from the dominant wavelength and therefore affect the color produced. [1|2|17|1471]

In Ducos du Hauron’s patented subtractive method, known as Heliochromy, three negatives were made behind separate filters of violet, green, and orange-red (the current modern subtractive filters had not yet been established). From these negatives, positives were made and assembled in register to create the final print, known as a Heliochrome. These positives contained carbon pigments of blue, red, and yellow, which Ducos du Hauron believed to be the complementary colors of the filters that were used to form the colors in the original exposure. Color prints or transparencies could be made with the assembly process, depending on whether the carbon transparencies were attached onto an opaque or transparent support. One of the first commercial subtractive assembly processes was the bichromated gelatin glue process, which was known as Trichromie and was patented by the Lumière Brothers in 1895. The assembly process is the principle used in the carbro process (see below). [1|2|18|1472]

Though the subtractive process proved to be practical, it saddled photographers with long exposure times. Ducos du Hauron reported typical daylight exposures of 1 to 2 seconds with the blue-violet filter, 2 to 3 minutes with the green, and 25 to 30 minutes behind the red filter. If the light changed during the exposure process, the color balance would be incorrect in the final result. This problem was solved in 1893, when Frederic E. Ives perfected Ducos du Hauron’s single-plate color camera. [1|2|18|1473]

Ives’s apparatus, the Kromskop Triple Camera, made three separate black-and-white negatives simultaneously on a single plate through red, green, and blue-violet separation filters. Positives were made by contact printing on glass, then cut apart and hinged together with cloth strips for use on Ives’s Kromskop viewer. This viewing system employed colored filters in the same sequence as the camera, and used a system of mirrors to optically superimpose the three separations and create a color Kromogram image. Although conceptually similar to Maxwell’s additive projection process, Ives’s color images could be seen after being assembled in this viewer (the Kromogram itself consisted only of image components). While Ives’s methods did work, they were complex, time-consuming, and expensive. [1|2|19|1474]