A PROCEDURE FOR THE CALCULATION OF BACKGROUND IN IMAGES

We present a routine that calculates the sky level of images. This rou tine is general in the sense that it can be applied to any image, inde pendent of the instrument with which it was obtained, to get a reliabl e value for the sky background. This is achieved by optimizing the par ameters of the calculation to give the best result for every frame. We compare the routine to other sky-calculating routines, and obtain sim ilar or more reliable results with our routine in all cases. The routi ne is currently implemented as a FORTRAN program within VISTA image-pr ocessing software, and it may be provided as a stand-alone FORTRAN pro gram after some minor changes.