IMCOMBINE

        input = "your spectrum list"     List of images
       output = ""     output image name
     (headers = "")             List of header files (optional)
     (bpmasks = "")             List of bad pixel masks (optional)
    (rejmasks = "")             List of rejection masks (optional)
   (nrejmasks = "")             List of number rejected masks (optional)
    (expmasks = "")             List of exposure masks (optional)
      (sigmas = "")             List of sigma images (optional)
     (logfile = "STDOUT")       Log file\n
     (combine = "average")      Type of combine operation
      (reject = "minmax")       Type of rejection
     (project = no)             Project highest dimension of input images?
     (outtype = "real")         Output image pixel datatype
   (outlimits = "")             Output limits (x1 x2 y1 y2 ...)
     (offsets = "none")         Input image offsets
    (masktype = "none")         Mask type
   (maskvalue = 0.)             Mask value
       (blank = 0.)             Value if there are no pixels\n
       (scale = "median")       Image scaling
        (zero = "none")         Image zero point offset
      (weight = "none")         Image weights
     (statsec = "")             Image section for computing statistics
     (expname = "")             Image header exposure time keyword\n
  (lthreshold = INDEF)          Lower threshold
  (hthreshold = INDEF)          Upper threshold
        (nlow = 1)              minmax: Number of low pixels to reject
       (nhigh = 1)              minmax: Number of high pixels to reject
       (nkeep = 1)              Minimum to keep (pos) or maximum to reject (ne
       (mclip = yes)            Use median in sigma clipping algorithms?
      (lsigma = 3.)             Lower sigma clipping factor
      (hsigma = 3.)             Upper sigma clipping factor
     (rdnoise = "0.")           ccdclip: CCD readout noise (electrons)
        (gain = "1.")           ccdclip: CCD gain (electrons/DN)
      (snoise = "0.")           ccdclip: Sensitivity noise (fraction)
    (sigscale = 0.1)            Tolerance for sigma clipping scaling correctio
       (pclip = -0.5)           pclip: Percentile clipping parameter
        (grow = 0.)             Radius (pixels) for neighbor rejection