Basic Photography Course

CHAPTER 10

IMAGE PROCESSING AND CONTROL

As a Navy photographer, you must realize that

composing and exposing a scene on film does not
guarantee top-quality photography. The quality of the

finished print depends on the quality of your darkroom
work. A perfectly exposed film is useless if it is fogged,
scratched, or under- or overdeveloped. Therefore, each
step of film processing is important and you must master
each step.

During the discussion of basic film processing

concepts, both black-and-white and color film
processing are covered. The mechanics of black and
white and color processing are very similar. The primary
differences between processing color film and
processing black-and-white film are there are more
steps in a color film process, and the time and
temperature requirements are more critical.

DEVELOPERS AND DEVELOPMENT

The purpose of development is to convert those

parts of the light-sensitive material (film or paper) that
has been affected by light to black metallic silver. This
produces a visible image from the invisible latent image.
Development is usually carried out by bringing the
exposed film into contact with a solution that contains a
developing agent, but no silver salt. The silver that forms
the developed image comes from a reduction of the
individual silver halide grains in the film emulsion. This
process is called chemical or direct development.

In another process that is seldom used, the

developed image is derived from a soluble silver salt
contained in the developing solution itself. This process
is called physical development. The physical
development process can be difficult to use because
there is a tendency for silver to be deposited where it is
not wanted.

The process of chemical development is most

commonly used for film development. Chemical
development is the process with which you should be
concerned. In chemical development, the individual
silver halide grains in the film emulsion are reduced to
a black metallic silver. Each grain in the emulsion acts
as a unit, in the sense that a grain is either developable
as a whole or is not developable. When film
development is performed properly, only exposed grains

containing a latent image are reduced to black metallic
silver. You may ask, "Why doesn't the developer
develop the unexposed grains as well as the exposed
grains?" Actually, the unexposed grains are develop
able. When development is carried out over a long
enough period of time, all grains are developed or
reduced to black metallic silver. The density that results
from the development of unexposed silver halides is
called fog. Thus development is a rate phenomenon and
the development of the exposed grains takes place at a
faster rate than the unexposed grains.

The individual grains of silver halide in an emulsion

are protected against the action of the developer by a
chemical layer. When light strikes the emulsion, it
breaks down the protective layer at one or more points
on each individual light-struck grain. When the exposed
film is placed into the developer, the grains are acted
upon at these points by the developing agent, and each
grain that received more than minimum exposure is
quickly reduced to black metallic silver. The amount of
blackening (density) over the film surface depends
primarily upon the number of grains that have been
affected by the developer. Density is also influenced
because some grains may not develop to completion in
the time the developer is allowed to act on the film.

COMPOSITION OF A DEVELOPER

There are many different formulas used as

developing solutions, but most developers contain the
following four essential ingredients: developing agent,
preservative, accelerator or activator, and restrainer.

DEVELOPING AGENT

The developing agent, commonly referred to as the

reducing agent, is the most important chemical in a
developing solution. It is the developing agent that
actually converts the silver halide grains in the emulsion
to metallic silver. Nevertheless, the other ingredients are
necessary to make the solution function properly.

One of the properties of a developing agent is its

reducing potential. This refers to its relative ability to
develop or reduce the silver halides. An active
developing agent attacks silver halides vigorously,

whereas one of low potential is slower in its action. For

10-1

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Basic Photography Course

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DOFMaster for Windows On-line Depth of Field Calculator DOFMaster for Mobile Devices On-line Depth of Field Table Hyperfocal Distance Chart Articles FAQ Recommended Books Support Contact Links Home As an Amazon Associate I earn from qualifying purchases.	contents <- previous page next page -> CHAPTER 10 IMAGE PROCESSING AND CONTROL As a Navy photographer, you must realize that composing and exposing a scene on film does not guarantee top-quality photography. The quality of the finished print depends on the quality of your darkroom work. A perfectly exposed film is useless if it is fogged, scratched, or under- or overdeveloped. Therefore, each step of film processing is important and you must master each step. During the discussion of basic film processing concepts, both black-and-white and color film processing are covered. The mechanics of black and white and color processing are very similar. The primary differences between processing color film and processing black-and-white film are there are more steps in a color film process, and the time and temperature requirements are more critical. DEVELOPERS AND DEVELOPMENT The purpose of development is to convert those parts of the light-sensitive material (film or paper) that has been affected by light to black metallic silver. This produces a visible image from the invisible latent image. Development is usually carried out by bringing the exposed film into contact with a solution that contains a developing agent, but no silver salt. The silver that forms the developed image comes from a reduction of the individual silver halide grains in the film emulsion. This process is called chemical or direct development. In another process that is seldom used, the developed image is derived from a soluble silver salt contained in the developing solution itself. This process is called physical development. The physical development process can be difficult to use because there is a tendency for silver to be deposited where it is not wanted. The process of chemical development is most commonly used for film development. Chemical development is the process with which you should be concerned. In chemical development, the individual silver halide grains in the film emulsion are reduced to a black metallic silver. Each grain in the emulsion acts as a unit, in the sense that a grain is either developable as a whole or is not developable. When film development is performed properly, only exposed grains containing a latent image are reduced to black metallic silver. You may ask, "Why doesn't the developer develop the unexposed grains as well as the exposed grains?" Actually, the unexposed grains are develop able. When development is carried out over a long enough period of time, all grains are developed or reduced to black metallic silver. The density that results from the development of unexposed silver halides is called fog. Thus development is a rate phenomenon and the development of the exposed grains takes place at a faster rate than the unexposed grains. The individual grains of silver halide in an emulsion are protected against the action of the developer by a chemical layer. When light strikes the emulsion, it breaks down the protective layer at one or more points on each individual light-struck grain. When the exposed film is placed into the developer, the grains are acted upon at these points by the developing agent, and each grain that received more than minimum exposure is quickly reduced to black metallic silver. The amount of blackening (density) over the film surface depends primarily upon the number of grains that have been affected by the developer. Density is also influenced because some grains may not develop to completion in the time the developer is allowed to act on the film. COMPOSITION OF A DEVELOPER There are many different formulas used as developing solutions, but most developers contain the following four essential ingredients: developing agent, preservative, accelerator or activator, and restrainer. DEVELOPING AGENT The developing agent, commonly referred to as the reducing agent, is the most important chemical in a developing solution. It is the developing agent that actually converts the silver halide grains in the emulsion to metallic silver. Nevertheless, the other ingredients are necessary to make the solution function properly. One of the properties of a developing agent is its reducing potential. This refers to its relative ability to develop or reduce the silver halides. An active developing agent attacks silver halides vigorously, whereas one of low potential is slower in its action. For 10-1 contents Basic Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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