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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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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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