Two separate CCD camera data acquisition systems have been built 
in the section (figure VI-A,B). The first is a stereo monochromatic image 
acquisition system in which the cameras are precisely synchronized to 
individual pixels. Synchronization is essential for metric processing of 
stereo images of dynamic processes. Currently, this system has a single 
shot frame grab mode and a slow serial link to a remote computer. It will 
be useful for acquiring small format test data. 
The second CCD camera unit is more complex and was designed for 
field data acquisition of Moire scoliosis screening data. It is capable of 
storing about 5 frames per second onto a 10 MB disk cartridge unit. The 
cartridges are removable, providing essentially unlimited storage of 
images in the field. The system operates like a digital polaroid camera. 
The image is previewed on a display then, when the desired frame is 
selected, it is recorded on disk. After being recorded, the image can be 
reviewed at once without off-line processing. This system is quite robust 
and portable even in its prototype form. It has realtime custom image 
processing hardware to perform image enhancement and symmetry correlation 
analysis. An estimate of symmetry is used to obtain an automatic trigger 
for recording the image, thereby performing a rudimentary automated data 
acquisition control function. 
3.0 SYSTEM FOR REALTIME PHOTOGRAMMETRY : APPLICATION SOFTWARE 
The system for realtime photogrammetry is used for two purposes: 
the automatic measurement of three-dimensional coordinates of object 
points for industrial applications, and the evaluation of the performance 
of CCD cameras. 
For the automatic measurement of targetted object points, a 
program which combines image processing, pattern recognition, and 
photogrammetric algorithms has been developed. The program, named OBJECT, 
is described in the block diagram [Figure VII]. There are eight processing 
steps, the first six of which are performed mostly by dedicated hardware 
and in real time. The system requires 10 to 20 milliseconds to perform 
these six steps on each target. The results are two sets of image 
coordinates, one from each camera, ready for matching and photogrammetric 
processing. The last two steps require 50 to 60 millisecond execution time 
for each object point. Some of the program operations are described below. 
For noise reduction, a sequence of images is taken, instead of 
only one, and averaged. Also the bias frame (or the dark-exposure frame) 
is subtracted from the scene image frame to remove built-in noise. 
The enhancement process is needed to emphasize important features, 
such as targets or edges, and suppress the others. Operations required for 
this purpose are a variety of linear and nonlinear filters and point-by- 
point mapping operations. The system has about fifty library filters and 
mapping functions to choose from. 
In the image segmentation process, the enhanced image is converted 
into a binary image for easier feature extraction. The threshold required 
for this operation may be different in different parts of the image, 
depending on the light conditions. Therefore, the image is divided into 
windows and a threshold is selected for each window separately. This 
operation requires histogramming each window and is carried out entirely 
by dedicated hardware. 
The result of the segmentation process is an image composed of 
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