Removing image contamination

  It is usually the case that any image containing a galaxy of interest will also contain a number of other objects such as galaxies, stars, cosmic rays or even image flaws. Those that fall on the image far beyond the apparent limits of the galaxy may be ignored, but those lying close to the galaxy of interest must be removed. The is because the profiling applications have been written under the assumption that the only sources of pixel count on the image are the one galaxy of interest and the image background noise. If an extraneous object lies within the outer, fainter, isophotes of a galaxy the software is unaware that the contaminated pixels contain contributions from an additional source and the profile generated is incorrect. For the purposes of ESP the contaminated pixels may be removed from the analysis by setting their values to bad.