The Equivalent Quantum Efficiency of the Photographic Process

Two approaches to the formulation of equivalent quantum efficiency (EQE) are considered. The first, in terms of the Selwyn granularity coefficient, defines the EQE on a macroscopic scale, whereas the second, by the application of Fourier analysis, shows the spatial frequency dependence of the EQE. It is demonstrated that whereas the second approach is rigorous, the first is only valid when using scanning apertures large enough to maximize the Selwyn coefficient. The use of smoller apertures can lead to over optimistic values of EQE, and it is reasoned that some of the previously published values of EQE are in error on this account. The close relationship between EQE and information content is indicated.