Help for PIXGRAD

PURPOSE
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PIXGRAD calculates the magnitude (slope) and direction (azimuth)
of the gradient at each pixel within an image.  The image of slope
values is saved in the first output dataset, and the azimuth image
is sent to the second output.

The gradients are computed by examining the four adjacent pixels 
(left, right, above, below) to the point being evaluated.  From these
pairs of points, a line-direction and a sample-direction gradient is
computed. The composite slope and azimuth are computed by a
trigonometric summation of these two gradients.

Prior to rescaling, the slope is computed as degrees from horizontal,
while the azimuth is degrees East of North.  The default rescaling
maps the slope values to 0 DN for horizontal and 255 DN for vertical.
The default azimuth rescaling places North at 0 DN, East at 64 DN,
South at 128 DN, and West at 192 DN.

EXECUTION
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Execution is initiated by:

pixgrad INP (OUT1,OUT2) PARAMETERS


LIMITATIONS
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Input image must be no more than 10,000 samples wide.