A priori knowledge of the image support, often called the support constraint, when applied to a raw image formed by an imaging system leads, by means of convolution with the support spectrum, to a mixing of the spatial frequencies in the image. For a noisy raw image, such mixing causes motion of noise in its spatial-frequency spectrum. A simple model for describing the motion of atmospheric-turbulence-induced noise in the spectrum of a star image formed by a ground-based system under the application of a support constraint is presented. The transport of noise occurs in this model by a combination of ballistic motion, or drift, and diffusive spreading. For an inversion-symmetric support, the drift is absent, and noise transport is exclusively diffusive. An analytical expression for the reduction of noise that such diffusive spreading in the spatial-frequency plane can facilitate, when a circular support of arbitrary size is employed, is derived.
© 1999 Optical Society of AmericaFull Article | PDF Article
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