Preliminary processing of images.
You must have the frames with a dark current and flat field for preliminary
processing of the images. The dark current taken with the same time of exposition
and at the same temperature as the CCD image, but with a shutter closed.
The flat field is necessary for the account of
the variations in the sensitivity of pixels. The image of a flat field obtain
at uniform light-striking of a field of sight. For example, it can be a frame
of a twilight sky.
If you want to take into account these effects, make the following:
1) Open the frame with a flat field by 
.
Press 
. In the
dialogue choose a frame with a dark current. There will be a subtraction of the
dark frame from the flat field.
Save the flat field on the disk by 
.
2) Open a frame (or frames) with observed
objects.
Subtract the dark current by 
.
3) Apply the flat field by 
.
Note If several files are open, a dark current and flat field will apply for all.