Equivalent Quantum Efficiency and the Information Content of Photographic Images

Abstract

Noise-equivalent quantum efficiency and responsive quantum efficiency of a photographic emulsion are explained and a definition of its information storage capacity at a given mean density level is formulated on the basis of Shannon's information theory. The definition involves the conventional assumption that the intensity distributions to be recorded by the emulsion are random and of low contrast. Some conventional assumption about these distributions is unavoidable because the Shannon information content of a received message does not depend only on the message itself. Currently available data about photographic emulsions only permit their information storage capacity to be evaluated over a restricted range of spatial frequencies. For photographic systems one can define the analogous concept of the informational equivalent quantum efficiency (bits per unit object-contrast density per photon). This concept provides a figure of merit for photographic systems which takes account in a physically significant way of the interactions between optical and photographic spreads, film speed, and photographic granularity.