(c) The green-recording layer is an orthochromatic emulsion and is
sensitive to both blue and green light.
Because of the colloidal silver,
only red and green light is allowed to penetrate to this point. Since this
emulsion layer is not sensitive to red and since all the blue light has been
absorbed, the only exposure possible at this point is that produced by green
(d) Following the green sensitive emulsion is a panchromatic
emulsion that records red.
This emulsion is manufactured with a very low
sensitivity to green.
Since the blue has not penetrated to this point,
because of the layer of colloidal silver, only a red record is made.
(2) Summary. In effect then, a sheet of negative or reversal color
film is made up of three separate emulsion layers, each one sensitive to or
able to record only one of the additive primary colors. Refer to figure 1-
c. Coupler Development.
The dye images in color processing are
supplied by the chemical reaction known as "coupler development."
action takes place in the color development step in all color film, both
negative and reversal.
(1) Coupler development in negative color film.
In all negative
color film, the couplers are located in the emulsion.
Examples would be
Ektachrome and Agfachrome film. This requires one re-exposure (or reversal
bath), which exposes all the silver halides that were not exposed during the
initial exposure. Since the couplers are located in the emulsion, only one
color developer is required to produce dye in all three sensitive layers.
(2) Coupler development in reversal color film.
In reversal color,
the couplers are located in the emulsion or in the color developer.
(a) The presence of the dye coupler in the color developer
solution necessitates the use of three developers, one for each dye. A few
commercial films, notably Kodachrome, use this type of processing, but it is
laborious and time-consuming, requiring elaborate equipment.
(b) Each color-sensitive layer must individually undergo the
second reversal exposure and then color development to form the proper dye
in that layer. Since only one layer at a time receives a second exposure,
dye will form only in that layer. Because the selectivity of dye formation
is determined by individual layer exposure, only reversal materials can be
processed by this technique.