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

Threshold+ is an enhancent version of a normal Threshold, it converts
images to black and white.

The + now is that it includes a kind of smoothing function to get rid of
quantization noise and isolated pixels. The smootheness is variable.

The algorith used for smoothing is very simple but also very fast.

 PERMSSN    UID  GID    PACKED    SIZE  RATIO     CRC       STAMP          NAME
---------- ----------- ------- ------- ------ ---------- ------------ -------------
[generic]                 6993   10708  65.3% -lh5- 04e8 Jul 18  1999 plugins2/Threshold+.pss
[generic]                 2740    7136  38.4% -lh5- 38aa Jul 25  1999 Threshold+.guide
---------- ----------- ------- ------- ------ ---------- ------------ -------------
 Total         2 files    9733   17844  54.5%            Jul 25  1999