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Authors: M. Bertero and P. Boccacci
Abstract: In this paper we propose a solution to the problem of reducing the boundary effects (ripples) in the deconvolution of astronomical images. The approach applies to the Richardson-Lucy method (RLM), namely the most frequently used deconvolution method in Astronomy, and is based on the idea of using RLM for attempting a reconstruction of the astronomical target in a domain broader than that of the detected image. Even if, in general, the reconstruction outside the image domain is not reliable, this approach, in a sense, is letting RLM to choose the appropriate boundary conditions and, as a consequence, the reconstruction inside the domain is considerably improved. We propose a simple implementation of this approach, allowing a reduction of its computational burden. Numerical experiments indicate that it is possible to obtain excellent results. Extensions and applications of the method are briefly discussed.

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Posted by: admin, on 11/1/2006, in category "2005"
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Authors: B.Anconelli, M. Bertero, P. Boccacci, M. Carbillet, and H. Lanteri
Abstract: In previous papers we proposed methods and software for the restoration of images provided by Fizeau interferometers such as LINC-NIRVANA (LN), the German-Italian beam combiner for the Large Binocular Telescope (LBT). It will provide multiple images of the same target corresponding to different orientations of the baseline. Therefore LN will require routinely the use of multiple-image deconvolution methods in order to produce a unique high-resolution image. As a consequence of the complexity of astronomical images, two kinds of methods will be required: first a quick-look method, namely a method that is computationally efficient, allowing a rapid overview and identification of the object being observed; second an ad-hoc method designed for that particular object and as accurate as possible. In this paper we investigate the possibility of using Richardson-Lucy-like (RL-like) methods, namely methods designed for the maximization of the likelihood function in the case of Poisson noise, as possible quick-look methods. To this purpose we propose new techniques for accelerating the Ordered Subsets - Expectation Maximization (OS-EM) method, investigated in our previous papers; moreover, we analyze approaches based on the fusion of the multiple images into a single one, so that one can use single-image deconvolution methods which are presumably more efficient than the multiple-image ones. The results are encouraging and all the methods proposed in this paper have been implemented in our software package AIRY.

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Posted by: admin, on 11/1/2006, in category "2005"
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Authors: B.Anconelli, M. Bertero, P. Boccacci, and M. Carbillet
Abstract: In the framework of the methods we introduced for the restoration of images of Fizeau interferometers such as the Large Binocular Telescope, we propose an algorithm which is able to super-resolve compact stellar objects such as a binary system with an angular separation smaller than the angular resolution of the telescope. The method, which works also in the case of a monolithic mirror, is based on a simple modification of the Richardson-Lucy (RL) method or of the Ordered Subsets - Expectation Maximization (OS-EM) method for image deconvolution. In general, it consists of three steps: the first one requires a large number of RL-iterations, which are used to identify and estimate the domain of the unresolved object; the second one is a RL-restoration initialized with the mask of the domain. These two steps can provide a super-resolved image of the stellar system but the photometry of the stars may not be correct. Therefore their positions are derived from the result of the first two steps while their magnitudes are estimated in a third step by solving a simple least-squares problem. In order to show that the method can work in practice, we use (simulated) adaptive-optics-corrected point spread functions (PSF), both in the case of a monolithic and in the case of a binocular telescope, and we investigate mainly the case of binary systems. We analyze the limitations of the method in evaluating the angular separation and the relative magnitude of the two stars. The results we obtain are quite promising.

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Posted by: admin, on 11/1/2006, in category "2005"
Views: this article has been read 7923 times