Once it is realized that thresholds, such as those for vernier alignment, are a small fraction of the classical Rayleigh resolution limit, the optical and information-theoretical consequences have to be faced. Transferring discussion into the spatial-frequency domain, in which the diffraction limit is embodied in the cut-off frequency (G. Westheimer, 1977), makes it clear that no physical principles are violated. Often, by a kind of Bayesian process, inferences are drawn about the target from the spectrum inside the cut-off frequency and prior expectation of associations with possible patterns beyond it. All this is in contrast to modern practices of optical super-resolution, which employ sophisticated stratagems to shift actual high-frequency components into the pass-band of the imaging device and hence require, as a consequence, sophisticated procedures for object reconstitution.
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