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The Improbability of the Photographic Process

  • Lawrence Slifkin


The very high sensitivity of silver halide photographic emulsions is the result of a surprisingly high quantum efficiency in the formation of the latent image, combined with a large amplification of the stored optical signal upon photographic “development.” The efficient formation of the latent image can be traced to the effects of an unusual set of physical properties of silver bromide and silver chloride, involving the electron energy band structure, the dynamics of photoelectrons, the nature and mobilities of the ionic point defects, and the existence of a sub-surface electric field.

Despite the current availability of a wide variety of optical recording systems, the standard silver halide photographic emulsion continues to offer a unique combination of sensitivity, resolution, tone quality, convenience, and economy. This article will outline the physical processes that operate in forming the image. It will emphasize the unusual set of properties of silver bromide and silver chloride that are involved, and that impart to the process its extraordinary efficiency. Only black-and-white images will be considered, but the same basic imaging process is involved in color photography as well.

This discussion is, of necessity, brief and often qualitative, but more complete treatments of the scientific aspects of the photographic process can be found in the other articles in this issue of the MRS BULLETIN, as well as in the bibliography.



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These references are to more detailed reviews of the physics of latent image formation and the relevant properties of the silver halides. Reference 1 also cites an extensive bibliography.

1.Hamilton, J.F., Adv. in Phys. 37 (1988) p. 359.
2.The Theory of the Photographic Process, 4th ed., edited by James, T.H. (Macmillan, New York, 1977).
3.The Physics of Latent Image Formation in Silver Halides, edited by Baldereschi, A., Czaja, W., Tosatti, E., and Tosi, M. (World Scientific, Singapore, 1984).
4.Mitchell, J.W., Rep. Prog. Phys. 20 (1957) p. 433; in Photographic Sensitivity, Vol. 3 (Maruzen, Tokyo, 1962) p. 23.
5.Brown, F.C., in Treatise on Solid State Chemistry, Vol. 4, edited by Hannay, B. (Plenum, New York, 1976) p. 333.
6.Brown, F.C., in Points Defects in Solids, Vol. 1, edited by Crawford, J. and Slifkin, L. (Plenum, New York, 1972) p. 491.

The Improbability of the Photographic Process

  • Lawrence Slifkin


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