The most inclusive parameter describing the performance of an imaging detec
tor may be considered detective quantum efficiency (DQE) expressed in funct
ion of the spatial frequencies. In this paper our effort is addressed to fo
rmulating a general and absolute expression of the DQE in the frequency dom
ain, coherent with the condition DQE less than or equal to QE. The case of
a flat-field input image and of integrating detectors is also considered. (
C) 1999 Elsevier Science B.V. All rights reserved.