MOPEX User's Guide - IRSA

OUTPUT
MOPEX User’s Guide
Generated Fits Files (*_minback.fits): The background subtracted, individual images.
DISCUSSION
This module is required if you plan to use Bright Object Masking, and carries out a median
background subtraction before running the Detect module to detect the bright objects in the
frame. The background-subtracted images are not used for later mosaicking.
With the default Median option, the program computes a background value using the median
of a running rectangular window of Window X by Window Y pixels, after omitting the
Outliers / Window highest pixels. This is done for each pixel so can be very slow.
If Use SExtractor background estimation is set, the module switches to the Sbkg background
estimation based on that of SExtractor (Bertin and Arnouts, AASupp 117, 393, 1996). The
image is divided into Panels with size given by Window X, Y. In each Panel, iterative clipping
is used to find a single estimate of the background in the Panel. You can optionally median
filter the Panel background values, e.g. to avoid ones where bright objects skewed the
background estimate. The median filter size is given by SExtractor background filter size. It
then interpolates the Panel values to find the background at each pixel. This is much faster
than calculating the median of a big window at each pixel.
Both background estimates generally give reasonable results, but if the data volume is large,
the Sbkg option is strongly recommended as it is much faster. It also does not require an
estimate of Outliers / Window.
4.3.6 Overlap Modules: Detect
Command Line Equivalent: run_detect
Default Output Directory: /Detect-overlap
De pe nds On: Initial Settings; Med Filter
Important Notes: Including this module does not automatically apply Bright Object Masking.
The resulting bright object detection maps are only used if the Mask Bright Object box is checked
in the Mosaic Interpolate module.
Overlap (overlap.pl) 37
Overlap Modules