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46
III. 16-MM FILM AND ITS CHARACTERISTICS
All color-reversal films are manufactured on the assumption that light of any color can be analyzed into three primary components. When the components are resynthesized, the original subject is reproduced in its original color. In practice, the accuracy of color reproduction is knowingly sacrificed to create results believed to be pleasing to the majority of viewers.
The theoretical background for color film and color photography is quite extensive and is beyond the scope of this book. Two outstanding texts are: The History of Three Color Photography, by E. J. Wall; and The History of Color Photography, by J. S. Friedman. It will probably be necessary to consult the former text in a library as it has been out of print for some time.
Figure IB is a diagrammatic representation of a color-reversal film such as AnscoColor or Kodachrome. White light provides an exposure
UNEXPOSED FILM
Blue-sensitive emulsion Green-sensitive emulsion Red-sensitive emulsion
PROCESSED FILM
Yellow image Magenta image Blue-green image
Safety film support
Antihalation backing
Fig. IB. Cross section of Kodachrome film. This is a typical multi layer integral tri-pack color film.
in all three layers ; blue light exposes the upper layer only ; green light exposes the middle layer only ; and red light exposes the lower layer only. (If there is no light there is no exposure.)
Practically, the film has no blue, green, or red filters. The method of analyzing the image into the three components and the manner in which these components are individually recorded will become apparent from the description that follows.
The upper emulsion layer of the film is sensitive only to blue. Green light and red light pass through it readily without affecting it. No blue light passes to either of the lower emulsion layers; a yellow dye is located between the top (blue-sensitive) layer and the middle (green-sensitive) layer to prevent its transmission.
The middle emulsion layer is sensitive to green light but is not sensitive to red light. Although it is sensitive to blue light, as are all silver emulsions, no blue light reaches it and there is therefore no exposure from blue light. Since it is sensitive to green light but not to red, only the green light causes an exposure in this layer.