Combining Bias Frames

Combination of the bias frames is straight forward: filters used and integration times do not play a role, and in most cases the bias frames can be treated with the same weight. The default keyword setting for the bias combining is displayed in Table 3.4.

 

Table 3.4: Keywords for combining bias calibration frames

Keyword	Content	Default	Description
CCD_IN	input name	?	table of input frames
BS_TYP	descriptor value	*	exposure type to check, if any
BS_SIG	yes|no	no	create sigma image
BS_MET	comb. method	maxrej	type of combining operation
BS_DEL	yes|no	no	delete cal. frames afterwards
BS_STA	mean|median|mode	mode	correct. by Mode/Median/Mean
BS_EXP	yes|no	no	scale by exposure time
BS_SCA	yes|no	no	scale by MMM
BS_OFF	yes|no	no	add offset from MMM
BS_WEI	yes|no	yes	use a weighted average
BS_SEC	area	[<,<:>,>]	area for finding MMM
BS_RAN	real,real	-99999,99999	valid pixel range
BS_CLP	real	3.,3.	low/high sigma clipping factor
BS_NUL	real	NULL(2)	value for rejections