Help for SBOXFLT

PURPOSE:
SBOXFLT applies a 2-d convolutional high-pass box filter to an input image
by taking the local mean of all pixels contained within a prescribed window 
centered at each pixel of the input image, with reflection performed at image 
boundaries.  Each input value is replaced with the difference between the 
input and the local mean, plus a constant DC-level offset of 128. The filter 
weights are equal to one within the box.  The degree of high-pass filtering 
applied is controlled by the box width and length which may be specified.
A lowpass option is available which replaces each input value with the
calculated local mean.

EXECUTION:
SBOXFLT invokes BOXFLT2 with the specified parameters.  See help for BOXFLT2
for the complete list of defaulted parameters used by BOXFLT2.

Examples:
	sboxfltx  INP  OUT  NLW=21  NSW=451

	This example performs a high-pass filter of size 451 samples by 21
	lines on the input. Reflection is performed at image boundaries.

	sboxfltx  INP  OUT  NLW=21  NSW=451 'lowpass

	This example performs a low-pass filter of size 451 samples by 21
	lines on the input. Reflection is performed at image boundaries.

Mode of handling boundaries:
		a = pixel (1,1)		b = pixel (1,NS)
		c = pixel (NL,1)	d = pixel (NL,NS)
			+-------+-------+------- 			| d   c | c   d | d   c |
			|       |       |       |
			| b   a | a   b | b   a |
			|-------|-------|-------|
			| b   a | a   b | b   a |
			|       |       |       |
			| d   c | c   d | d   c |
			|-------|-------|-------|
			| d   c | c   d | d   c |
			|       |       |       |
			| b   a | a   b | b   a |
			+-------+-------+------- 				RELECTION
OPERATION:
SBOXFLT applies a 2-d convolutional high-pass box filter to an input image
by taking the local mean of all pixels contained within a prescribed window 
centered at each pixel of the input image, with reflection performed at image 
boundaries.  Each input value is replaced with the difference between the 
input and the local mean, plus a constant DC-level offset of 128. The filter 
weights are equal to one within the box.  The degree of high-pass filtering 
applied is controlled by the box width and length which may be specified.
A lowpass option is available which replaces each input value with the
calculated local mean.

WRITTEN BY:  
COGNIZANT PROGRAMMER:
REVISION:  Made Portable for UNIX   Richardson(CRI)  31-Oct-94