- Long_bsample is used (Nod & Shuffle uses mos_bsample) to define the background

- have to do each one individually
gm> gsex stgsgtN20040911S0116

- Found better traces if aperture width is changed to include wings, if needed (:upper, :lower or can change ap_width individually with 'y)

- Note: once an image has been processed with gsextract, it is necessary to delete the corresponding database files ("./database/") before re-reducing the image with different background subtraction parameters. Otherwise, the old parameter values in the database will silently override the user-specified values.

     (outprefix = "e")         Output prefix
     (refimages = "")          Reference images for tracing apertures
    *(apwidth = 2)           Extraction aperture in arcsec (diameter)
     (fl_inter = yes)          Run interactively?
     (find = yes)              Define apertures automatically?
     (recenter = yes)          Recenter apertures?
     (trace = yes)             Trace apertures?
     (tfunction = "chebyshev") Trace fitting function
     (torder = 3)              Trace fitting function order
    *(tnsum = 10)	       Number of dispersion lines to sum for trace
    *(tstep = 50)	       Tracing step
    *(weights = "variance")    Extraction weights (none|variance)
    *(clean = yes)             Detect and replace bad pixels?
    *(lsigma = 3.)             Lower rejection threshold for cleaning
    *(usigma = 3.)             Upper rejection threshold for cleaning
    *(background = "fit")      Background subtraction method
     (bfunction = "chebyshev") Background function
    *(border = 1)              Order of background fit
    *(long_bsample = "*")      LONGSLIT: backgr sample regions, WRT aperture
    *(mos_bsample = 0.5)       MOS: fraction of slit length to use (bkg+obj)
    *(bnaverage = -10)         Number of samples to average over
     (bniterate = 2)           Number of rejection iterations
     (blow_reject = 2.5)       Background lower rejection sigma
     (bhigh_reject = 2.5       Background upper rejection sigma
     (bgrow = 0.)              Background rejection growing radius (pix)