The median filter is a much used and sometimes misunderstood tool available to image processing specialists. It should now be clear to readers that the median is not an alternative filter to those described in this text. It is simply a special case, one of many options that might arise from the design techniques should it happen to be the optimum for that example.
The general filter described above is a rank selection filter in that the output value of the filter always corresponds to one of the inputs. The filter is unable to average or interpolate and this means that it does not produce simple blurring. However, filters with larger windows can give streaking effects in images. This will be addressed later in the chapter.
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