More sort thoughts
Late last night when I should really have already headed to bed I had some more thoughts on the median filter and played a bit with a batchers sort generator.For a 9 value median, rather than do a full 9 element sort, one could just do an 8 element sort and then attempt to insert the final value into the middle. The insert which only must be valid for the centre value only takes 2 additional
cas steps. But an 8 sort takes quite a few fewer steps than a 9 sort, and even then 2 are redundant for finding the median. In short, this allows a 9 element median to be calculated in only 19
cas operations rather than 22.
For larger sorts one can probably repeat the process further.