Computer Investigation of a Latent-Image Model*

Abstract

The paper describes a method for computing the response of a hypothetical photographic emulsion, given a detailed model for latent-image formation and development. A digital computer generates a random sequence of events simulating those which occur during and after exposure of a photographic grain. The computer records all of the active centers which form as a result of these events, and gives as a final result the number of silver specks of each size. The application of some developability criterion to these data determines whether or not the grain is developable and how many development centers it contains. The process is repeated until an adequate sampling of grains is represented, and the results are compared with data from actual emulsions. The method yields D–log E, reciprocity-failure, or development-center distribution characteristics. The authors propose a model as a working hypothesis to explain the response characteristics of a simple photographic emulsion [ H. E. Spencer R. E. Atwell , J. Opt. Soc. Am.54, 498 ( 1964); H. E. Spencer L. E. Brady J. F. Hamilton , ibid. 54,492 ( 1964)]. This model contains many features in common with the Gurney–Mott mechanism of latent-image formation, including: reversible electron-trapping; ionic neutralization of trapped electrons; recombination; thermal decay of single silver atoms; permanent hole-trapping; permanent electron-trapping at silver aggregates, etc. The effects of changes in various physical parameters on photographic response are determined. The study shows that the observed effects of sulfur sensitization of this emulsion can be simulated by moderate increases in the depth of electron traps and in the stability of single silver atoms.