Help for PIXSTAT


PURPOSE

	PIXSTAT is a VICAR applications program for calculating statistical
	quantities in local areas surrounding each pixel in an input image.
	The local mean, second moment, variance and standard deviation are
	quantities that may be obtained.

EXECUTION FORMAT

	PIXSTAT IN OUT [NLW,NSW,SCALE,OFFSET,CALC]

	where

	IN	is the input data set (VICAR labeled image).

	OUT	is the output image of the selected statistic.

	NLW	is the number of lines in the local area window.
		This number must be odd to insure a center line.
		The default value is 11. The maximum value is 129

	NSW	is the number of samples in the local area window.
		This number must be odd to insure a center sample.
		The default value is 11. The maximum value is 129

	SCALE	is the scaling factor that each output pixel will be
		multiplied by. The default value is 1

	OFFSET	is the constant which is added to each scaled pixel
		befor it is output. The default value is 0

	CALC    is a keyword selecting the statistic to be calculated.
		'MEAN, 'MOMENT, 'VARIANCE and 'SDEV (standard deviation)
		are the valid selections. 'SDEV is the default selection.

		All numerical parameters are integers.
OPERATION

	PIXSTAT performs a sliding window statistical analysis on an input
	image. An output pixel's position represents the center position of
	the window for the input image and its value represents statistics
	based on data within the window only. The window moves along one sample
	at a time and one line at a time until each pixel in the input has
	been at the center of the window. In other words statistics are 
	compiled for the local area around each and every pixel in the input
	image.

	The edge conditions are handled as follows. Any window positions that
	extend beyond the edge of the image are handled by using data from the
	nearest pixel on the image. This is not a reflection scheme like some
	sliding window algorithms have.

	Half word input results in half word output. Byte input results in
	byte output. This is automatic and requires no specification by the 
	user. Half word values that exceed the half word maximum integer value
	(32767) are set to 32767. Similarly byte values that exceed 255 are
	set to 255. Input images must have less than 4001 samples. There is
	no limit to the number of lines in the input.
EQUATIONS

	MEAN
		The mean is a result of the sum of all DN values in the 
		window divided by the number of pixels in the window.
		(the average of the DNs)
			WINDOWSUM / NPIXWNDO




	SECOND MOMENT
		The second moment is a result of the sum of the squares 
		of all DN values in the window divided by the number of
		pixels in the window. (the average of the squares of the DNs)

			DNSQRSUM / NPIXWNDO

	VARIANCE
		The variance is the difference between the second moment
		and the square of the mean.(average square - average squared)

			SECOND MOMENT - MEAN ** 2

	STANDARD DEVIATION
		The standard deviation is the square root of the variance.

			VARIANCE ** 0.5


Original Programmer:	Leo Bynum    March 1985
Cognizant Programmer:	Leo Bynum 
Revision		3	     May 1988