function get_res_offset, item
;
;+
;NAME:
;	get_res_offset
;PURPOSE:
;	Given an image resolution, return the value of the digital
;	offset for that resolution.
;CALLING SEQUENCE:
;	x = get_res_offset(index)
;	x = get_res_offset(roadmap)
;	x = get_res_offset(indgen(3))
;METHOD:
;	The input can be a structure or a scalar.  The structure can
;	be the index, or roadmap, or observing log.  If the input
;	is non-byte type, it assumes that the bit extraction had
;	already occurred and the "mask" is not performed on the input.
;INPUT:
;	item	- A structure or scalar.  It can be an array.
;OUTPUT:
;	returns	- The digital offset in DN for that resolution.
;HISTORY:
;	Written 12-Nov-91 by M.Morrison
;FUTURE OPTIONS TODO:
;	Optionally look at the exposure duration and adjust the
;       offset to compensate for dark current buildup.  Could even
;       look at the temperature
;-
;
lookup = [13.5, 30.0, 69.]
;
res = gt_res(item)
out = lookup(res)
;
return, out
end