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EO. PARALLAX
SIGNAL REGISTRATION SIGNAL
REGISTRATION | ERROR SIGNAL PARALLAX
ANALYZER
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—O PARALLAX
IMAGE SIGNAL
SIGNAL
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ANALYZER [—*—O sicNAL
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MULTIPLYING | y. O vELOCITY
CORRELATOR SIGNAL
Figure 8. Correlation Unit
1. A shaft position representing terrain slope
for contour steering. (T.S.D.)
2. Avoltage representing terrain slope magnitude
(T.S.M. signal), used to control size of the
scanning pattern.
Nature of Image Signals — Figure 9
Any image is made up of areas differing
in density and separated by boundaries. It is
the boundaries that produce signals useful for
alignment purposes. The first curve shows the
ideal waveform produced by an infinitely small
scanning spot crossing perfectly sharp bound-
aries. The spot is assumed to be moving across
a bright band on a dark background, giving first
a positive and then a negative boundary signal.
The second curve shows the smoothing effects
of spotsize and image unsharpness. The signals
from the photo-cells are filtered to reduce both
high-frequency quantum noise and low-frequency
signals from large image detail. The effect of
filtering is shown in the third and fourth curves.
-—DARK— —--—— LIGHT ——— — DARK—
I
IDEAL BOUNDARY
WAVEFORM
EFFECT OF FINITE
SPOT SIZE
EFFECT OF LOW
PASS FILTER
|
|
1
EFFECT OF HIGH & LOW
PASS FILTERS
I
|
Figure 9. Boundary Waveforms
AUTOMATIC STEREO (Appendix)
RIGHT SIGNAL O
LEFT SIGNAL O
IMAGES MISALIGNED
MISALIGNMENT:
zi
5
Figure 10. A simple Multiplying Correlator
Multiplying Correlator — Figure 10
The multiplier is an electronic circuit that
provides an output signal approximately pro-
portional to the product of the two input signals
at any instant.
When the left and right optical axes are
aligned to corresponding points in the images,
the scanning spots cross corresponding image
boundaries simultaneously to give the conditions
shown in the first set of waveforms. Since the
boundary signals in both channels have the same
polarity, the multiplier outputis always positive.
The low pass filter smooths the output to pro-
vide a more or less steady signal.
When parallax is present, the scanning
spots cross corresponding image boundaries at
different times. The resulting boundary signals
reach their maximum values at different times
as shown in the second set of waveforms, giving
a smaller product or output signal. The output
of a multiplier is zero if either input factor is
zero, therefore greater parallax than that shown
could give zero output.
Registration Discriminator — Figure 11
The figure 11 illustrates a simple regis-
tration discriminator using a quadrature network
and a multiplier. A study of the waveforms will
show that the polarity of the output depends upon
which image signal is leading in time. The out-
put is therefore, a registration error signal.
In summary, the action of the registration
discriminator is as follows:
1. Under conditions of perfectregistration of the
images with the optical axes, the output is
zero.
2. With moderate misalignment, the output will
be positive or negative depending upon which
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