Sextractor for dummies - METU Astrophysics

30 CHAPTER 7: SE INPUT: THE CONFIGURATION FILE
This is the description from the SE manual v2.3:
NONE: No weighting is applied. The related WEIGHT IMAGE and
WEIGHT THRESH (see below)parameters are ignored.(quick toggle so
you can see if including the weight image has any effect)
BACKGROUND: the science image itself is used to compute internally
a variance map (the related WEIGHT IMAGE parameter is ignored).
Robust (3 -clipped) variance estimates are first computed within the
same background meshes as those described in x12. The resulting
low-resolution variance map is then bicubic-spline-interpolated on the
y to produce the actual full-size variance map. A check-image with
CHECKIMAGE TYPE MINIBACK RMS can be requested to examine
the low-resolution variance map.
MAP RMS: the FITS image speci ed by the WEIGHT IMAGE le name
must contain a weightmap in units of absolute standard deviations (in
ADUs per pixel).
MAP VAR: the FITS image speci ed by the WEIGHT IMAGE le name
must contain a weightmap in units of relative variance. A robust scaling
to the appropriate absolute level is then performed by comparing this
variance map to an internal, low-resolution, absolute variance map built
from the science image itself.
MAP WEIGHT: the FITS image specified by the WEIGHT IMAGE file
name must contain a weight-map in units of relative weights. The data
are converted to variance units (by definition variance / 1=weight), and
scaled as for MAP VAR. MAP WEIGHT is the most commonly used
type of weight-map: a flat-field, for example, is generally a good approximation
to a perfect weight-map.
In fact, if you want to work with Weight maps (since you think you have something
that might be used as a weigth map), please read section 7 in the official
manual.