.sp
.LP
These routines filter images in the spatial domain.
.SH
SHORT DESCRIPTION OF ROUTINES
.IP "Median (quick sort) -" 20
Perform a median filter on an image using quick sort to find the 
median value.
.IP "Median (histogram) -" 20
Perform median filtering on an image using a histogram to find
the median.
.IP "Sobel -" 20
Perform image differentiation by running two NxN weighted operators 
on an image (Sobel filter).
.IP "Gradient -" 20
Sharpen an image by differentiation (gradient).
.IP "DRF Edge Extract -" 20
Difference recursive filter.
Optimal filter for edge detection.
.IP "GEF Edge Extract -" 20
First derivative operator for symmetric exponential filter.
Edge detection using maxima of gradient.
.IP "SDEF Edge Extract -" 20
Second derivative operator for symmetric exponential filter.
Edge detection using zero crossings of 2nd directional derivative
along the gradient.
.IP "Speckle Removal -" 20
Reduce speckle noise from an image by using the Crimmins algorithm.
.IP "2D Convolution -" 20
Compute the two-dimensional convolution of a pair of images.
