.LP
These routines use two images to produce a single output
image.  They also may use a masking image to gate what is used 
from one of the input images.  The operations are arithmetic
operations performed on a pixel by pixel basis from the two
images.
.SH
SHORT DESCRIPTION OF ROUTINES
.IP "Addition -" 20
Add two images pixel by pixel.
.IP "Subtraction -" 20
Compute the difference (subtract) between two images pixel by pixel.
.IP "Multiplication -" 20
Multiply two images pixel by pixel.
.IP "Division -" 20
Divide two images pixel by pixel.
.IP "Absolute Difference -" 20
Compute the absolute difference between two images pixel by pixel.
.IP "Blend Images -" 20
Blend two images using X*image1 + (1-X)*image2, where X is the
blend ratio.
