If two point-sources are close together so that their images overlap, the
detection algorithim for detecting point-sources will either fail to detect
one or both. However, the detection algorithm for detecting extended sources
will either pick up the missing object or detect both as a single extended source.
An extended source may consist entirely of pixels below the detection threshold,
and therefore will not be detected, even though the source is clearly visible on the
image. The parameter nsigma controls the detection threshold and, if necessary,
this can be decreased from its default value of 2 to the minimum allowed value of 1.
Please note that using this value may significantly increase the execution time..
