Proposed performance measures for imaging systems with discrete detector arrays

Abstract

The paper discusses how a description of an imager in terms of its optical transfer function is not appropriate for digital or discretely sampled imaging when aliasing occurs, since these optical systems transform high spatial frequencies into low frequencies. The link between perception and the detection of distinguishing features is discussed. On the basis of this link, it is proposed that two new performance measures are introduced. The rst, a circle contrast function, measures the ratio of the detector response to a small bright circle to the detector response to an equally bright large circle. The second proposed measure records how bright a small circle must be in the scene for it to be resolvable in the display. The mathematical derivation of the circle contrast function from the optical transfer function is given. It is also shown how the point spread function may be obtained from the circle contrast function when the point spread function is approximately Gaussian. Finally the paper describes how the sensitivity index d 0 may be obtained from these two performance measures. This quantity d 0 , which arises from signal detection theory, relates to the ability of an observer to perform the various perception tasks.