The capability of the CLEAN algorithm, which is able to develop image information corresponding to spatial frequencies for which the imaging system’s optical transfer function (OTF) is equal to zero, is shown to be dependent on the limited size of the object being imaged. It is found that this capability is available without a severe signal-to-noise-ratio penalty only for the recovery of a spatial frequency that is sufficiently close to some other spatial frequency for which the OTF is not equal to zero. As used here the term “sufficiently close” means that the magnitude of the separation of the spatial frequencies is less than one half of the inverse of the size of the object being imaged. This represents a limitation of CLEAN’s capability deriving from object size. It is suggested that this capability can be thought of in terms of superresolution, with the same limitation in regard to object size.
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