Color print film is composed of eight or
more microscopically thin layers, three to four of which contain
embedded silver halide crystals and adjacent color dye couplers. The
silver, at first, and eventually the dye couplers alone, work together
to reproduce the full spectrum of color that we see in a fully
processed color negative or color print.
When color film is exposed to light,
silver halides undergo a chemical change. They are sensitized by the
light, in much the same way blackand-white film is, and they form an
invisible or latent image. When the film containing this latent image
is subjected to immersion in a chemical color-developing agent, each of
the color layers containing silver halides undergoes further chemical
changes. Initially, halides are converted to black silver. Next, color
couplers form dye clouds in one of three subtractive primary colors
(yellow, magenta, or cyan).
Parts of the original scene photographed
that were blue are represented on film in the yellow dye layer.
Wherever green existed in the scene, that is now represented in the
magenta layer, and red subject matter becomes part of the cyan dye
layer of the negative. In sum, white appears black, blue records as
yellow, green as magenta, and red as cyan in the bottom dye layer. It
is important to note that dye clouds are not solid opaque blocks of
color. They are color specks of varying densities, representing
chromatic differences in specific colors. Dye clouds exist at different
depths from top to bottom and, when viewed via transmitted light,
combine to present a full color replication of the original scene.
Eventually a fully processed negative is placed in an enlarger or other
printing device, light is passed through the negative, and a full
spectrum of color exposes sensitized color-printing paper. Before
getting to the printing stage, several additional steps are necessary
to complete film processing.