of Microprocessors

CONTROL SEQUENCE DISPLAY AND EDITING 361
UNEDITED
CURVE
EDITED CURVE
WITHOUT
INTERPOLATION
EDITED CURVE
WITH
INTERPOLATION
100% ~
0%-/[ cE~D'ITT I1"-
-I INTERVAL'-
~I
TRANSITION
INTERVAL
Fig. 11-8. Interpolation window
copied to another curve over a specified interval. Contours could also be
swapped or even called up from a library of contours that had been successfully
used earlier. Note that these are nonreversible functions. The editing
software should have provisions for saving the status of things before a
nonreversible function is performed.
At this point, a potential problem is seen. These editing changes can
result in a discontinuity at the boundary between edited and unedited portions
of the curves. What is needed is a method of interpolation so that the
boundary transitions are smooth. Figure 11-8 should be helpful in visualizing
how such interpolation might be done. A key concept is the idea of an
interpolation window. An interpolation window is itself a curve that varies
between 0% and 100%. In use, it is applied to two curves; the original
unedited curve and the edited but not interpolated curve. The result is a
third, interpolated curve that actually consists of a weighted sum of the first
two curves. In effect, the interpolation window specifies how to weight the
sum. At the 0% points, the result is equal to the unedited curve. At the 50%
points, the result lies midway between unedited and edited curves. At the
100% point, it is all edited curve. As can be seen, interpolation considerably
smooths the transition between unedited and edited segments.
In use, no single interpolation window shape is ideal for all situations.
One variable is the width of the transition interval relative to the edit
interval. Another is the shape of the transition interval itself. Although the