EDP Sciences
Free access
Issue
A&A
Volume 401, Number 2, April II 2003
Page(s) 797 - 807
Section Physical and chemical processes
DOI http://dx.doi.org/10.1051/0004-6361:20030137


A&A 401, 797-807 (2003)
DOI: 10.1051/0004-6361:20030137

A robust algorithm for sky background computation in CCD images

F. Patat

European Southern Observatory, K. Schwarzschild Str. 2, 85748 Garching, Germany
(Received 24 October 2002 / Accepted 24 January 2003)

Abstract
In this paper we present a non-interactive algorithm to estimate a representative value for the sky background on CCD images. The method we have devised uses the mode as a robust estimator of the background brightness in sub-windows distributed across the input frame. The presence of contaminating objects is detected through the study of the local intensity distribution function and the perturbed areas are rejected using a statistical criterion which was derived from numerical simulations. The technique has been extensively tested on a large number of images and it is suitable for fully automatic processing of large data volumes. The implementation we discuss here has been optimized for the ESO-FORS1 instrument, but it can be easily generalized to all CCD imagers with a sufficiently large field of view. The algorithm has been successfully used for the UBVRI ESO-Paranal night sky brightness survey (Patat 2003).


Key words: techniques: photometric

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