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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.
Next: Removing consistent image faults
Up: ESP Extended Surface Photometry
Previous: Local background value determination
ESP --- Extended Surface Photometry
Starlink User Note 180
Norman Gray
Mark Taylor
Grant Privett
27 January 2000
E-mail:ussc@star.rl.ac.uk
Copyright © 2002 Council for the Central Laboratory of the Research Councils