Modern color films are constructed much the same as black-and-white film, but color films consist of three separate emulsions on a single film base. Each of the three emulsion layers records one of the three additive primary colors-red, green, or blue. The top emulsion layer is sensitive to blue light and produces yellow dyes. Between the top emulsion layer and the middle emulsion layer is a yellow filter (fig. 2-3). The yellow filter absorbs the blue light that would otherwise affect the middle and bottom emulsion layers. During processing, this yellow filter is dissolved. The middle emulsion layer records green light and produces magenta dyes. The bottom emulsion records red light and produces cyan

dyes. Many of the modern high-speed color films have fast and slow emulsion layers for each primary color (fig. 2-4).

In some color films where tabular-grain (T-grain) emulsions are used, high speed and increased sharpness are combined. When these films are manufactured, the overall thickness of the film is reduced By reducing the overall thickness, you also reduce the scattering of light within the film, resulting in improved sharpness. Also, double-emulsion layers, one fast and one slow, may be incorporated to improve film speed in color films.

Each emulsion layer of color film either has an incorporated dye coupler or a dye that is put into the emulsion during processing. A dye coupler is a chemical that produces a dye by combining with the oxidized products that occur during color developer.

Color Negative Film

A color negative film records a scene in image densities opposite to the brightness of objects in the scene-the same as a black-and-white negative film. Color films can be recognized because they contain the suffix color, such as Vericolor, Kodacolor, and Fugicolor. These color films are used when a print is the final product. Most color negatives (other than color film used for aerial photography) have an orange mask This orange mask increases the color separation that reproduces colors more accurately in the final print.

During development, colors are formed in the emulsion that are complementary to the color of the original scene; for example, a red object in the scene is recorded as cyan in the negative. It is a combination of yellow, magenta, and cyan that records all the other colors that you see in the scene. Color dyes in the emulsion layers control the colors of light passing through the color negative.

Color negative film images can be printed on color positive materials, such as color paper and color print film, to produce color prints or color transparencies.

Color negatives can also be printed on a special panchromatic black-and-white paper to produce black-and-white prints.

Color Reversal Film

Color reversal films produce positive images in densities directly proportional to the reflective brightnesses of objects and in the same colors as those in the original scene. Reversal films are recognized by the suffix chrome in their names, such as Ektachrome, Kodachrome, and Fujichrome.

The positive image of most color reversal film is produced by a two-stage development process. This

process causes chemical fogging and color developing of the portions of the silver halide emulsions that were not affected by camera exposure or the first black-and-white developer. Like color negative film, color reversal film has three emulsion layers that are sensitive to blue, green, and red light and produces yellow, magenta, and cyan dyes, respectively. The film contains dye-forming chemicals that are put into the emulsion layers during manufacturing. A color developer produces three dye images in the emulsion layers. The three dye images in a developed color reversal film control the colors of light passing through the film.

Kodachrome film does not contain dye-forming chemicals in the emulsion layers. They are introduced during processing from three separate color developer solutions. Kodachrome film has high resolving power and tine grain and produces a fine image. Processing Kodachrome film is a complex operation and can only be performed by a Kodak processing plant.

Developed color reversal film can be used as a transparency (slide) for direct viewing, printed directly onto a color reversal paper, copied on a black-and-white film for producing black-and-white prints, or copied to a color internegative (copy negative) for producing color prints.

Color Balance

Color balance is the acceptable relationship among the three color images in a positive color print or slide. This means that when the color print or slide looks correct, color balance has been achieved.

To help achieve this acceptable relationship, the manufacturer balances color film emulsions for

exposure with a specific Kelvin temperature (K). Remember, daylight usually has a higher content of blue light than red light, while tungsten illumination usually has a higher content of red light than blue light. To compensate for the lower proportion of red light in daylight, the manufacturer balances color films for daylight, so they have a higher sensitivity to red light than to blue light. To compensate for the lower proportion of blue light in tungsten illumination, the manufacturer balances color films for tungsten illumination, so they have a higher sensitivity to blue light than to red light.

Generally, color films are referred to as daylight (outdoor) or tungsten (indoor), indicating their broad use without filters. Specifically, daylight films are balanced for use in sunlight or with an electronic flash

2-6 that averages approximately 5400 K. Tungsten films are balanced for use with illumination of 3200 K without filtration.

The Kelvin temperature of the exposing light for reversal films is much more critical than the color of the exposing light for color negative films. When an exposing light is used other than that for which color negative film is balanced, adjustments to the filter pack can be made during printing to achieve proper color balance. With color reversal film, however, a slide is usually the final product. When the color of the exposing light is other than that for which the film is balanced, the transparencies are off-color. You should strive to expose all color films with the color light for which the films are balanced.

Although color films have three separate emulsions, only one ISO film speed is assigned. An ISO film speed for color film is most accurate when the illumination used is the one for which the film is balanced.