International projectionist (Jan-Dec 1956)

Color and Its Reproduction on Film By ROBERT A. MITCHELL All factors which contribute to high-quality color projection are thoroughly explored in the third and final installment of this article. Getting the most out of color prints has become a vital part of the projectionist's job in the wide-screen era. COLOR FILMS used for theatre movies at the present time may be divided into two main groups: imbibition (dye-transfer) prints and multilayer (dye-coupler) prints. The old "duplitized," or double-coated, type of color film has practically disappeared from the field. Imbibition prints are made by transferring colored dyes soaked up by the gelatin relief images of specially prepared "matrix" positives to blank release-print stock. Three successive printings are necessary, one for each primary color involved in photography. The printing dyes are complementary in color to the primaries, the blueviolet image being printed in lemon, the green image in magenta, and the red image in cyan. The blank printing stock is ordinary 35-mm positive having only a sound track and framelines in developed silver image. Least Expensive Method The imbibition process, employed exclusively by Technicolor, is the least expensive way to make color motionpicture prints. Complex equipment operated by specially trained operators is required. Multilayer dye-coupler color films have the color "built in." Coated with three very thin black-and-white emulsions, each containing dye-forming chemicals and sensitized to only one of the three primary spectral colors, ihis type of film is printed from reversed-color negatives and developed in much the same way as ordinary film. The silver image formed in each of the three layers is bleached out during processing after the corresponding dye-image has been formed by chemical action. The sound track and framelines are printed in the color emulsion-layers, hence require no special treatment as in Technicolor. (Technicolor printing dyes are too transparent to "low red" and infrared wavelengths, and give images too blurry, to allow the use of dye-image sound tracks.) Eastman Color, Ansco Color, and Agfacolor are among the most widely used multilayer color films. Eastman Color is frequently issued under trade names given it by producing companies and processing laboratories. Technicolor imbibition prints may easily be distinguished from multilayer color prints on casual inspection by the appearance of the framelines. These are printed in silver image in Technicolor films, and are light gray in color. The framelines of multilayer films, on the other hand, are so dark as to look almost black. Technicolor Sound Tracks The sound tracks on Technicolor prints are exactly similar in appearance to those on black-and-white prints, while those on multilayer Clumps of opaque silver in black. &c white emulsion ilm ba.se A/WVvVWWWVWVvjg VISIBLE RAYS INFRARED RAYS Color-film dyes that absorb light but mit infrared rays Film base Both visible light and invisible infrared rays are absorbed and converted into heat by the opaque silver particles of black-and-white emulsions. The dye images of color films, on the other hand, transmit the infrared radiation and are heated by the visible rays alone. Color prints are accordingly able to withstand arc currents that would blister the emulsion of monochrome prints. prints are often much darker, and sometimes have a blueviolet tinge. (Very rarely they have an all-over amber tint.) Viewed by reflected light at a large angle of incidence, the picture images on most multilayer color films appear slightly more embossed than those on Technicolor imbibition prints. Scraping the emulsion very carefully with a sharp knife or razor blade in a dark area of the image reveals another difference between multilayei and imbibition films. As the emulsion of a multilayer film is scraped, the top magenta-image layer is removed first, leaving a green image. Further scraping removes the cyan layer, leaving the lemon (actually yellow) emulsion. Similar careful scraping of the emulsion of a Technicolor film removes all colors at the same time, resulting only in a faded image. There are no separate color layers, for the three dye images are printed on the gelatin coating of regular positive stock. But when Technicolor film is soaked in a hot solution of baking soda, the magenta dye diffuses much more readily than either the cyan or lemon; and scraping will then reveal a magenta image which has penetrated the gelatin completely. This does not happen with similarly treated multilayer films. Projection Characteristics Notwithstanding these slight physical differences, the picture images on both imbibition (Technicolor) and multilayer (Eastman Color) prints are dye images, no silver being present. In projection, therefore, both types of color film behave very nearly the same — a behavior noticeably different from lhat of black-and-white film. The silver images of black-and-white prints absorb all wavelengths of radiation about equally. These images are composed of microscopic clumps of opaque silver that absorb all wave 16 INTERNATIONAt PROJECTIONIST • FEBRUARY 1956