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.