Level 2 Help for BOXFLT2

NSW is the width in pixels of the box filter.  It must be less than
twice the image width in pixels and defaults to 11.

NLS is the length in lines of the box filter.  It must be less than
twice the image length in pixels and defaults to 11.

FILTER=HIGHPASS specifies that the output is to be the highpass, rather than
the lowpass, version of the input, i.e., OUT = IN - LOW + DCLEVEL.
The default is lowpass filtering.

Specifies (for highpass filter) the constant to be added to the 
difference (IN-LOW) in the highpass output image.  Default is 128.

Specifies image handling at image boundaries.  Setting EDGE=CYCLE or 'CYCLE
causes the program to treat the image as if it wrapped around at boundaries
in both directions.  'LCYCLE and 'SCYCLE cause wrap-around in the line and
sample direction only, respectively.  'EXTEND causes the edge pixel to be
repeated for all locations beyond the boundaries. The default is for the 
program to reflect the image at the boundaries.