and since the blue light is absorbed by the colloidal silver, only a red
record is made.
In effect then, a sheet of color film is made up of three separate emulsion
layers, each sensitive to or able to record only one of the three additive
primary colors of light.
Subtractive primary colors, such as yellow, are
recorded in the two layers that combine to make up the color (e.g., green
and red). White light is recorded in all three levels.
2.
Transmitting Colors Correctly for Prints.
The basic difference between negative and reversal color processing is that
negative film is processed in a single, color developer. The amount of dye
produced is directly related to the exposure the particular film layer
received during camera operation.
In addition, color negative film uses
colored couplers in forming the middle and lower dye layers.
a. How Dye Layers Work. After color film is completely processed, all
that is left are the three different layers of dye. The primary purpose of
these dyes is to control transmission and absorption of red, green, and blue
light. However, even the best available dyes produced in color film absorb
some of the light that they should transmit. This is true in negative and
positive color films since the dyes used are the same.
(1) For example, a perfect cyan dye would absorb only red light and
would transmit green and blue light freely.
All known cyan dyes absorb
large proportions of green and blue light.
(2) Similarly, a perfect magenta dye would absorb only green light,
transmitting blue and red light freely.
Magenta dyes transmit red light
freely, but absorb some blue light.
(3) Of the three dyes used (cyan, magenta, and yellow), yellow is the
closest to ideal.
Yellow absorbs blue light and transmits green and red
light.
b. Using Masking. The effect of the unwanted absorption of the dyes is
not a serious disadvantage in a positive color transparency used only for
projection or direct viewing.
The real difficulty is noticeable when you
make a duplicate or a color print from the transparency. Since the dyes in
the reproduction material are the same as the dye in the original, the
errors are multiplied in the reproduction. To produce satisfactory results,
supplementary masking must be used for correction of color prints.
2-3
SS0514
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