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