This is one of my plugins for ArtEffect2/3+.

Rank-Order-Filters are a known family of filters including: Minimum, Maximum
and Median. This plugin can be each of them and anything between.
It is much faster than ArtEffect's Minimum, Maximum and Median and has
more functionality.

The filter sorts all the colors around the filtered pixel by brightness and
takes the color at the user selected rank.

 PERMSSN    UID  GID    PACKED    SIZE  RATIO     CRC       STAMP          NAME
---------- ----------- ------- ------- ------ ---------- ------------ -------------
[generic]                11081   19712  56.2% -lh5- 3b4c Jul 25  1999 plugins2/RankOrder.p2m
[generic]                11147   19868  56.1% -lh5- 0668 Jul 25  1999 plugins2/RankOrder.p2n
[generic]                11077   19700  56.2% -lh5- f4ce Jul 25  1999 plugins2/RankOrder.p4s
[generic]                 3019    7772  38.8% -lh5- 7f93 Jul 25  1999 RankOrder.guide
---------- ----------- ------- ------- ------ ---------- ------------ -------------
 Total         4 files   36324   67052  54.2%            Jul 25  1999