i 
end 
image matching and data extraction. An accompany- 
ing paper* describes the basic principles of optical 
correlators and discusses their application to photo- 
grammetric data processing, emphasizing the capabili- 
ties of these devices to process large image areas 
simultaneously. Since optical correlators avoid the 
process of scanning the imagery and converting it to a 
time-domain signal, they overcome much of the 
inherent speed-sensitivity limitation of flying-spot 
scanners. Figure 124 shows a comparison of the 
theoretical signal-to-noise ratio of comparable elec- 
tronic and optical correlators for low-contrast im- 
agery of high spatial bandwidth. Significantly, the 
optical correlator performance is independent of 
spatial frequency (within the frequency limit of its 
optical aperture, 280 line-pairs per millimeter), and 
the signal-to-noise ratio can be greatly superior when 
a laser power of greater than a few hundred milliwatts 
is used. A limitation of the present optical correlators 
is the difficulty of compensating for image distortion. 
The present systems compensate only for first-order 
distortion and require additional optical elements to 
introduce rotation and anamorphism. While there are 
a number of potential techniques for improving and 
simplifying distortion correction, much development 
remains to be done in this area. 
  
        
      
  
  
300 
Space- Bandwidth Limit 
100 1— : Region Ci 
Optical With Higher Power 
Correlator 
(100 MW Laser) 
36 + 
z 
o 
2 
S 
t€ 101— 
$8 
© Electronic 
T Correlator 
> 
$ s— 
o 
- 
3 
= 
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1 dl 
Contrast 
031— Modulation = 4% 
Average Density 
0 1 2 3 
o11— | | — 
0 0.1 0.01 0.001 
Average Intensity Transmittarice T 
Figure 12 Signal-to-Noise Ratio Performance of the 
Optical and Electronic Correlators 
AUTOMATION IN COMPILATION 
Scanning 
Signals Deflection 
Image Fourier Image x. wv and 
    
Plane 
  
Plane Transform 
Image 
Intensifi 
  
Input 
Photograph 
Figure 13 Camera-Tube Scanning System 
Another area of interest is the application of 
camera tubes to image scanning. The image dissector 
is of particular interest because it avoids the require- 
ment of the vidicon and the image orthicon for a 
highly regular scanning pattern and is fully as flexible 
as the flying-spot scanner in this respect. Figure 13 
illustrates some of the advantages of a camera tube 
system. Spatial filtering, employed before the scan- 
ning process, can be used to improve the contrast of 
the scanned image and to emphasize components of 
the imagery which contribute to the x-parallax deter- 
mination. The image intensifier is needed, in general, 
to provide sufficient light input to the image dissector 
to achieve a high signal-to-noise ratio. In the optimum 
system, the image intensifier and image dissector 
would also provide integration or smoothing of the 
electronic image analogous to that provided in the 
vidicon and image orthicon. The major barrier to the 
application of these techniques at the present time is 
that the basic components, the image intensifier and 
the image dissector, are not yet fully developed for 
this application. However, recent work at Bendix 
Research Laboratories in the application of the Chan- 
neltron®* miniature electron multipliers to these 
problems shows substantial promise. 
Other potential flying-spot scanner replacements 
might be mentioned, for example, the deflected laser 
beam, but each has fundamental limitations which are 
yet to be overcome. At present there is no alternative 
available which can compete with the flying-spot 
scanner and electronic correlator on all fronts. 
*S. J. Krulikoski et al, “Coherent Optical Parallel Processing.” 
1 This figure has been taken from an acompanying paper, “A Com- 
parison of Optical and Electronic Correlation Techniques," by D. C. 
Kowalski. 
(Q* Registered trademark, The Bendix Corporation. 
11