In this paper we have extended the OS-EM method, which was introduced in computed tomography, to the restoration of LBT images. The method provides a considerable acceleration of the usual Lucy-Richardson method, denoted in this paper as LR/EM method. Indeed the computational cost of one iteration is approximately the same for the two methods but the number of iterations required by OS-EM is smaller than that required by LR/EM by a factor of the order of p, the number of LBT images corresponding to different orientations of the baseline. As a consequence, in the case of OS-EM the computation time for obtaining a reliable restoration is approximately independent of (or weakly dependent on) the number of LBT images. Moreover we have shown by means of numerical simulations that OS-EM and LR/EM provide in practice the same results as concerns the restoration errors and the evaluation of astrometric and photometric parameters.
Our IDL codes for the two methods are free and available on request to the authors.
Acknowledgements
This work was partially funded by CNAA (Consorzio Nazionale per l'Astronomia e l'Astrofisica) under the contract No. 16/97. We thanks Maurizio Busso, Mario Gai and Mario Lattanzi, from Osservatorio Astronomico di Torino, Serge Correia, Andrea Richichi and Piero Salinari, from Osservatorio Astrofisico di Arcetri, as well as Piero Calvini from Dipartimento di Fisica, Universita' di Genova, for several useful discussions and suggestions. We also thanks Serge Correia and Andrea Richichi for providing the images used in this paper to compare EM and OS-EM.
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