flatcombine

        input = @flats.lis      List of flat field images to combine
      (output = "flat.imh")     Output flat field root name
     (combine = "average")      Type of combine operation
      (reject = "avsigclip")    Type of rejection
     (ccdtype = " ")            CCD image type to combine
     (process = no)             Process images before combining?
     (subsets = yes)            Combine images by subset parameter?
      (delete = no)             Delete input images after combining?
     (clobber = no)             Clobber existing output image?
       (scale = "median")       Image scaling
     (statsec = choose it)      Image section for computing statistics
        (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 (neg
       (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)
       (pclip = -0.5)           pclip: Percentile clipping parameter
       (blank = 1.)             Value if there are no pixels
        (mode = "ql")