For creating one or more sky illumination correction frames the command ( SKYCOR/CCD) is available. Similar to other corrections, sky frame frames will first be processed according to the processing keywords ( SC_SCAN, SC_TRIM, SC_PXFIX, SC_BSCOR, SC_DKCOR, SC_FFCOR). After this calibration step, the command will smooth the reduced sky frame(s).
Input for the command can be either a single sky frame, or the CCD reduction
table containing a column with sky frames. Output can, obviously, a single
illumination frame, or a list of illumination frames. In the later case
these frame names will be stored in the column :IL in the reduction
table. It that doesn't exist yet it will be created. Default input and
output are taken for the keywords CCD_IN and CCD_OUT,
respectively. Smoothing parameters are taken from the the IL_...
keywords, which are listed in Table 
.