Kodachrome Film Is Sensitive: The top emulsion of Kodachrome film is sensitive tt blue light only. Beneath it is a layer of yellow dye thai absorbs the recorded blue rays, but allows the red and green rays to penetrate to the two emulsions beneath it, one of which is sensitive to green rays only, and the other to red. Thus, upon exposure a simultaneous record, in ktent image form, is obtained of the three primary colors in the scene. The film is first developed to a negative and then, by reversal processing, to a positive. During the second development dyes of the complementary colors of yellow, cyan, and magenta are formed in the appropriate areas, and the silver is bleached away.
The eye has its greatest sensitivity in the green, is less sensitive to blue and violet, and is not at all sensitive to ultraviolet. This accounts for the fact that an average landscape photographs differently, with respect to tone values, than the eye sees it. In the average photograph of a landscape, the trees appear abnormally dark and the sky abnormally light. This is because light from the sky is especially rich in blue, violet, and ultraviolet, to all of which the film is particularly sensitive, and to which the eye is comparatively insensitive. On the other hand, trees reflect much green light, to which the eye is very sensitive and to which the film is much less sensitive.
These techniques have the same limitation as the daguerreotype and the tintype: each color photograph is unique. The negative-positive principle was utilized in Kodacolor film (1941), which is similar in general principle to Kodachrome film, except that the image is not reversed to a positive. Dye-coupling development directly converts each emulsion to an image complementary to the color it records. Thus a color negative shows not only reversal of the lights and shades, but also of color. A blond will appear with blue hair and green lips. From this negative any number of prints can be made by repeating the process with identical triple emulsion coated on a white base.
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Photography
