Encyclopedia of Twentieth-Century Photography

(Note: Sample material is taken from uncorrected proofs. Changes may be made prior to publication.)

Color Theory: Natural and Synthetic

Photographic color theory is based on light and specific colors of light in the visible spectrum, which combine together to form what we call white light. Color can be broken down further into three elements: hue (the wavelength of color), saturation (the intensity of color), and value (the lightness or darkness of a color, sometimes also referred to as brightness). These components make up all photographic light. Black and white photography records light based only on value or brightness, and color photography records light based on two color sets: the additive primaries and the subtractive primaries. These sets are groupings of color that register in the human eye and on the surface of photographic materials. These two color groupings, when mixed together, make up all of the color combinations in photographic imaging.

The color wheel is made up of six colors, and red, green, and blue are placed directly inverse of cyan, magenta, and yellow. The additive primaries are red, green, and blue (also called RGB colors), and when mixed together form white light. The subtractive primaries are cyan (bluish-green), magenta (purplish-pink), and yellow (also called CMY primaries), and when mixed together from black or the absence of light. The six colors in the photographic process create a color wheel with complimentary pairs: blue and yellow, green and magenta, and cyan and red. On the color wheel, a triangle is created by both the RGB primaries and the CMY primaries as they are spaced alternately in the six color slots of the color wheel. Mixing the colors on either side of that hue creates each color in the wheel: for example, mixing green and blue creates cyan. These three-color pairs are linked through all traditional film and digital photographic processes. Each set of three primaries can form all six colors, and the additive primaries are used when taking a picture and affect the film, while the subtractive primaries are used for color printing. This is also true in digital imaging: the RGB primaries are used when reproducing color with light, such as a computer screen or television. The CMY primaries are used for printing with the addition of black.

Early color experimentation consisted of photographic material sensitive to red, green, and blue light. Antoine and Louise Lumière invented the Autochrome process in 1907, based on additive color theory. They covered a glass plate with potato starch grains sensitive to three layers of color: red-orange, green, and violet. When light passed through the glass, it was recorded on emulsion sensitive to only the specific color of the potato starch grain that the light passed through and its corresponding wavelength. This created a color transparency, but the process was labor-intensive and unstable. The subtractive color process was introduced into film with the invention of the Kodachrome process in 1935, developed by Eastman Kodak and Leopold Mannes. This process was popular with professional photographers for advertising and portraits, and rarely used by consumers because of its technical sophistication and expense. The consumer photographic market and fine art photography relied heavily on black and white film and developing until the 1970s when color film was significantly improved by manufacturers such as Eastman Kodak and Fuji. Aesthetic photographic history also changes in the late 1960s as photography is combined with other mediums such as silkscreen, and color is more readily accepted as a vehicle for photographic artists from the 1970's to the present.

Kodachrome film was made up of three layers of emulsion on the film, each sensitive to red, green, and blue light. This process was the origin of all subsequent color film. Color film has three layers of emulsion, each sensitive to one third of the spectrum (red, green, and blue). When the film is exposed, a latent image is created on each layer and the development process of color film produces a multi-layered negative.

The development process of color film creates the colors in the negative or positive image, negative if the film is to be used to create a photographic print; positive is the film is to serve as a slide or larger-format transparency. Color developing of film occurs when the developing agent is added to the film and dye couplers are activated for each color layer: the area sensitive to red light forms a cyan image, the area sensitive to green light forms a magenta image, and the area sensitive to blue light forms a yellow image. These three layers are then bleached to remove excess silver, and a color composite of all three subtractive hues is formed in the film emulsion. This process is similar in photographic paper and both positive and negative color film. The most widely used process for color negative film is Kodak's C-41, which produces a chromogenic color negative created by dye couplers. Color transparency film has a step that reverses the color process and the tonal range of the film. The standard process for transparency film is Kodak's E-6, but Kodachrome film is processed is a slightly different manner, Kodak's K-14 process.

Color film is affected by exposure, and over or underexposing slide or positive as well as negative film will change the saturation and value of color. Transparency or slide film has less exposure latitude than negative film, and is affected more by exposure variations. Overexposing slide film will desaturate and lighten the colors in the image, while underexposing slide film will saturate and darken the color range of the image. Color negative film has greater exposure latitude than transparency film, and quality color prints can be produced from under and over-exposed negatives that display little difference in hue and saturation from that of an properly exposed negative. Different film types and brands can also skew color balance, and some films produce a warm tone while others lean more to the cool side of the color spectrum. Color is also affected by film speed. Fast films have less saturation, color contrast, and smoothness than slower color films. Graininess is also an issue with fast film and this texture increases as the film's speed (also known as ISO and ASA) increases. Slow color film has a richer color palette, smother color forms, and a higher contrast than high-speed film.

Color printing is also a subtractive process. A negative is placed in a color enlarging head, and light is projected through the image onto photographic paper. The filter set of a color enlarging head allows for different amounts of cyan, magenta, and yellow to be adjusted for color balance. The strength of each filter is indicated by its density: the higher the filter number the denser the filter and the less light permeating through that filter. Color balance is achieved by adjusting the filter pack on an enlarger to create an image with neutral shadow and highlight areas. Viewing filters are useful for assessing color balance in color prints and are available in sets of six colors with varying densities for viewing color prints from transparencies and negatives. The subtractive primaries are the only colors used for printing because they make up the rest of the color scale and also merge to form black or the absence of light. In color darkroom printing, yellow is a combination of red and green, magenta is a combination of red and blue, and cyan is a combination of green and blue. Thus, the subtractive printing process in the darkroom allows for all six colors in the photographic spectrum to be created in color prints from negatives or transparencies. Color prints from negatives are often called chromogenic color prints and use a RA-4 color process, and color prints from transparencies use similar processes called Type R, R-3000, or Ilfachrome (formerly Cibachrome.) Printing from transparencies produces a higher contrast image with more color saturation than printing from color negatives. Additional color printing processes used in the color darkroom include dye diffusion and dye sublimation prints. Color photographic paper has a variety of qualities, and the paper type instead of the filter pack used in black and white printing affects the contrast range of color paper. Papers are available in a range of subdued to bright and saturated tones, and the photographer can choose the type of paper needed based on his subject matter and vision. By combining color film types and printing papers, a vast color range is available for photographers.

Digital imaging follows a similar process utilizing the additive and subtractive primary colors. The additive primaries correspond to the CCD (charged-coupled device) sensors in a digital camera or scanner and the subtractive primaries, with the added color black, are used for printing digital images. Digital cameras and scanners have CCD sensors that each register red, green, or blue through a grid of translucent image elements. A combination of these three colors will create any of the 256 color possibilities available on a digital screen or computer monitor. RGB colors are transferred to a binary number that is associated with a specific pixel or picture element for each piece of the scanned document or image area, and along with binary information on brightness, value, and tonal range are reassembled by a computer to make a digital picture. The individual red, green, and blue areas are seen together on the screen on a monitor and have a similar breakdown in television broadcasts. Editing digital images with software such as Adobe PhotoShop usually takes place in two color spaces or modes of calibration: RGB mode (red, green, and blue) and CMYK mode (cyan, magenta, and yellow.) CMYK mode is often called process color because black (represented by K) is added to the printer pack Black is abbreviated by K, which stands for key color, because it is the tone by which all other colors are aligned in the printing press.

Individual color layers called channels make up each mode with the appropriate color breakdown and these channels are displayed as layers of color in a digital imaging program. RGB mode is used for viewing images on the screen, and digital information is captured in this mode through a scanner or digital camera. Most scanners and digital cameras use CCD sensors sensitive to red, green, and blue, but a drum scanner is also capable of creating a digital composite with PMT (photo multiplier tubes) that record more information than traditional CCD film sensors. CMYK mode is used for printing and mimics the cyan, magenta, and yellow tones projected through an enlarger by a filter pack in traditional darkroom color methods. However, in CMYK mode the color black is added because combining cyan, magenta, and yellow does not produce a true black with inkjet pigments. Color balance in digital imaging is also done by using three color pairs in the same manner as traditional darkroom methods: yellow and blue, green and magenta, and cyan and red are all linked together and manipulate the overall color of a digital image. Hue, saturation, lightness or brightness, and exposure can also be manipulated through advanced imaging software applications.

Color in photography is used for a variety of purposes, including emotional and symbolic reasons and has an effect on the viewer's perception of an image. Color is subjective and arbitrary in many photographic images, and seeing a specific color or group of color hues can affect the mood and composition of an image. Juxtaposing color combinations can also change the reception of specific hues and neutral areas of white or black can take on a colorcast: if a green object is placed next to a white area in a photograph, the white area will take on some of the green hue of the adjacent space. The amount of white and black in an image can also alter how the brightness of specific colors are perceived, and brightness is often an arbitrary and subjective interpretation which is also influence by the type of light in which an image is viewed. The amount of perceived difference in adjacent colors is called color contrast, and is often separate from an individual color's value. Warm colors, which range in the spectrum from red to yellow, and cool colors that range from green to purple or violet, are called analogous hues. Analogous hues are also seen as having similar qualities, and when used together in a color image lower that images' overall color contrast.

Jennifer Headley

See also: Digital Photography; Dye Transfer

Further Reading

Joseph Ciaglia, Introduction to Digital Photography. (2002)

Peter Glendinning, Color Photography: History, Theory, and Darkroom Technique. (1985)

John Hedgecoe, The Art of Color Photography. (1984)

Robert Hirsch, Exploring Color Photography. (1992)

Henry Horenstein, Color Photography: A Working Manual. (1997)

Erika Kendra, Color Companion for the Digital Artist. (2004)

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