The X-ray vignetting function can be approximately removed with the
routine SXT_OFF_AXIS. Example calling statements are:
IDL> data_out = sxt_off_axis(index, data, index_out)
IDL> data_out = sxt_off_axis(index, data, /update_index)
IDL> vignette = sxt_off_axis(index, /vignette_only)
SXT_OFF_AXIS calls SXT_VIGNETTE to calculate the SXT X-ray vignette
function. See SXT Calibration Note 37 and the Instrument Guide of this
manual for more information. Two Vignette functions have been determined:
the high-energy function is applied to the Al12 and Be119 filters and
the low-energy function is applied to all other filters. Note that this
approach is somewhat approximate and care should be used when applying this
correction to SXT data.