The dark frame map contains all non-uniformities across the CCD surface. It will be shifted additively by CAL_offsetCorrect with the offset available either from CCF ADUConv or as the output of rgsoffsetcalc.
The dark frame will be stored in parameterized form in CCF DarkFrame on a per node basis. The functional form is
with parameters to and to that are available from CCF DarkFrame.1
Modifications of the dark frame due to light leaks from imperfections of the Al-filter will be included.
This routine is mainly used by CAL_gainCorrect to obtain the local offset at the position rawX & rawY.