SIMBAD references

We present an algorithm for achieving background consistency in overlapping images. The algorithm consists of two main steps. First, the images are interpolated to a common grid. Second, the cumulative pixel-by-pixel difference between the overlapping areas of all pairs of images is minimized with respect to the unknown constant offsets of the input images. The images are corrected by adding the computed offsets. Optionally, detection and masking of bright objects in the images can be performed prior to minimization. This option is especially useful for images with a high density of cosmic-ray hits. We use simulated data to optimize the algorithm in order to achieve a trade-off between the speed of execution and the quality of the background matching. We also show several examples of the application of this algorithm to real Spitzer data. The algorithm has been implemented and successfully used by the Spitzer image processing package MOPEX (Makovoz & Khan) and deployed by the Spitzer automated pipeline.