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If the stereo images are relatively distorted and must be transformed 
before complete registration can be achieved, local parallaxes will still 
remain within the superimposed image area and the sign and magnitude of the 
corresponding error signals will vary from point to point within this area. 
Under these conditions the parallax analyzer will deliver fluctuating error 
signals having an average value of zero but having instantaneous values and 
polarities representative of the parallax existing in the area being scanned 
at any instant. 
The fluctuating parallax signals from the parallax analyzer are called 
composite registration error signals and contain the information necessary 
to direct the transformations which must be applied to the images in order 
to achieve complete registration. The registration analyzer receives the 
composite registration signals from the parallax analyzer and X and Y 
reference signals from the raster generator. From these four inputs the 
registration analyzer computes 10 error signals, each of which is a measure 
of the correction needed in each of the 10 prime first- and second-order 
transformations already described. 
Signals from the raster generator when applied to the cathode ray tubes 
of the viewer and the flying spot scanners produce a square scanning raster 
in each case. The transformation circuits develop AX and AY signals 
which, when added to the signals from the raster generator, modify the shape 
of the rasters on the flying spot scanner tubes. Since the raster on the 
viewer tubes remains square, the imagery as seen by the operator suffers 
transformations complementary to the change in the shape of the flying spot 
rasters. 
The AX and AY signals delivered by the transformation circuits are 
under the control of the 10 transformation error signals from the registration 
analyzer. If no registration error exists, then all error signals will be 
zero and the AX and AY outputs from the transformation circuits are also 
zero. Under these conditions the flying spot rasters remain square and no 
transformation of the imagery as seen by the operator results. If, however, 
registration is incomplete, then one or more prime transformation error sig 
nals will be present and a corresponding set of AX and AY signals will 
be generated by the transformation circuits. These signals, when added to 
the signals for a square raster, will produce on the face of the flying spot 
scanners a transformation of the type required to produce registration. 
Here, again, transformations will be applied to the left and right scanning 
rasters equally but in opposite senses. 
The operation of the parallax analyzer, registration analyzer, and trans 
formation circuits is described later in the paper. Since the operation of 
these circuits and the ability to detect parallax in two dimensions are tied 
up intimately with the nature of the scanning pattern employed, we will con 
sider first and in some detail the characteristics of scanning patterns and 
their relation to the nature of the image information to be utilized.