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

Average is a high-speed and -quality implementation of a standard
Average Blur. Average is different to Gaussian Blur, the smoothing effect
is stronger and not completely independent of direction.
It looks more refracted.

 PERMSSN    UID  GID    PACKED    SIZE  RATIO     CRC       STAMP          NAME
---------- ----------- ------- ------- ------ ---------- ------------ -------------
[generic]                 2828    7216  39.2% -lh5- b843 Jul 21  1999 Average.guide
[generic]                 9956   16448  60.5% -lh5- cfcf Jul 21  1999 plugins2/Average.p2m
[generic]                 9952   16456  60.5% -lh5- 6654 Jul 21  1999 plugins2/Average.p2n
[generic]                 9890   16372  60.4% -lh5- 2b1e Jul 21  1999 plugins2/Average.p4s
---------- ----------- ------- ------- ------ ---------- ------------ -------------
 Total         4 files   32626   56492  57.8%            Jul 25  1999