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Extracting quantitative information from movie film and video recordings has always been a difficult process. The Galatea motion analysis system represents an application of some powerful interactive computer graphics capabilities to this problem. A minicomputer is interfaced to a stop-motion projector, a data tablet, and real-time display equipment. An analyst views a film and uses the data tablet to track a moving position of interest. Simultaneously, a moving point is displayed in an animated computer graphics image that is synchronized with the film as it runs. Using a projection CRT and a series of mirrors, this image is superimposed on the film image on a large front screen. Thus, the graphics point lies on top of the point of interest in the film and moves with it at cine rates. All previously entered points can be displayed simultaneously in this way, which is extremely useful in checking the accuracy of the entries and in avoiding omission and duplication of points. Furthermore, the moving points can be connected into moving stick figures, so that such representations can be transcribed directly from film. There are many other tools in the system for entering outlines, measuring time intervals, and the like. The system is equivalent to "dynamic tracing paper" because it is used as though it were tracing paper that can keep up with running movie film. We have applied this system to a variety of problems in cell biology, cardiology, biomechanics, and anatomy. We have also extended the system using photogrammetric techniques to support entry of three-dimensional moving points from two (or more) films taken simultaneously from different perspective views. We are also presently constructing a second, lower-cost, microcomputer-based system for motion analysis in video, using digital graphics and video mixing to achieve the graphics overlay for any composite video source image.
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