The SXT vignette function was determined from pre-launch calibration data obtained
at White Sands Missile Range (WSMR) and was further refined using flight data.
The vignette function is approximated by two non-concentric cones. The
routine SXT_VIGNETTE computes the SXT vignette function for a given SXT
image as described in the scalar SXT 
as follows:
IDL> vignette = sxt_vignette(index) ; SXT Index should be a scalar
IDL> vignette = sxt_vignette(array)
IDL> vignette = sxt_vignette(index,energy)
If 
is given then 
and 
0, 1, or
2, for full, half and quarter resolution. The second argument, 
will specify whether to use the low-energy results (derived from C-K and
Al-K test data) or the high-energy results (derived from Ag-L test data).
SXT_VIGNETTE is called by SXT_OFF_AXIS to correct SXT images. A quick
summary is available by typing:
IDL> help_vignette ; Display SXT vignette function