      medianfilter output (fmin) (fmax)

      Read a series of image names from standard input.  The input images
      must all be the same dimensions, and are expected to correspond to
      matching pixels.  For each pixel, the data values are sorted.  The
      data values within the range (fmin) to (fmax) are selected, where
      (fmin) and (fmax) are fractions between 0 and 1, and represent the
      fraction of the sorted stack of pixels.  The mean of the selected
      data within this range is then calculated.  The output file consists
      of pixels with these output values.