When light strikes one of these crystals, a photon(the
particle form of light) raises the energy level of loosely bound
electrons in the crystal’s halide salt. The electrons unite with
positive holes in the silver portion of the crystal to form a pure
atom of silver. In color film, crystals in different layers are
sensitized to respond only to red, blue, or green light rays.4
The pattern of millions of silver grains forms a latent
image, one that is not yet visible. Color film forms
three latent images, one for each of the layers
devoted to a specific color. To make the image visible,
the film is processed through a chain of chemical baths. The
first is a reducing agent, commonly called developer, that
converts silver ions into silver metal.5
The grains that make up
the latent image develop
faster than the other crys-
tals. The right combination
of temperature, agitation,
and time is followed by a
stop bath solution that
neutralizes the reducing
agent before it changes
the unexposed grains.6
Afixing bathdissolves the unexposed and therefore undeveloped
remaining silver halide that was not exposed to the light, leaving only the
silver metal behind to form, in black-and-white film, a negative of the pat-
tern of light the camera’s lens had projected onto it.7
In color film, chemicals called
couplersare matched with the
color-sensitized silver halide in
each of the three color layers. During
developing, the couplers form red,
green, or blue dyes concentrated around
the silver grains left by the reduction
process. After a brief drying, the film is ready
to produce prints or to become slides.8
CHAPTER 7 HOW LIGHT BECOMES DATA^101