Automation in motion - computer-assisted video systems for motion analysis

Science News, April 6, 1985

The swimming of fish, the flexing of a runner's foot, the movement of a robot reaching foir a tool are all examples of motions the researchers want to analyze. In many cases, the analysis is still done by filming the action, projecting the images on a screen and manually measuring changes in position from one frame to the next -- a tedious, time-consuming process. Now, motion analysis is speeding up with the introduction of sophisticated, computer-assisted video systems that automatically track and tabulate the trajectories of moving objects.

In the ExpertVision system developed by Motion Analysis Corp. of Santa Rosa, Calif., a video camera views, for example, a group of microscopic organisms flitting about in a drop of water. An electronic device, which reads 2,000 different shades of gray, converts each incoming, analog picture into a digital image that shows only the outlines of the objects of interest. Everything darker than a certain gray level, selected according to the contrast between the objects and their background, is represented by a one; everything lighter than that is a zero.

At 60 frames per second, the video processor tracks up to 250 separate moving objects at the same time, providing a list of coordinates for all of their outlines. A computer program organizes these data by linking the coordinates into groups that represent individual objects. A researcher can then ask for anything from a simple plot of a particular particle's path to a complex statistical analysis.

"The key to bringing an instrument like this to product status," says William G. Hand, one of the company's founders, "was the development of high-speed supermicrocomputers." These machines were needed so that computations could be done quickly enough to allow convenient motion analysis. The imageprocessing softwere itself, however, conceptually hasn't changed much, says Hand. It was first developed more than a decade ago by John O.B. Greaves when he was a graudate student at the University of California at Santa Barbara.

"The system can be used in virtually any application in which motion is a factor," says company president Sue W. Smith. One system, for example, is now being used by a shoe manufacturer to improve the design and performance of its running shoes. Another, at the University of California at Davis, tracks the motility of sperm in human fertility studies.

A rival motion analysis system, SELSPOT II developed by Selective Electronic, Inc., in Valdese, N.C., uses a different method for capturing the initial images. Infrared light-emitting diodes are attached to a number of points on, say, the head of a golf club or the body of a dancer. The diodes flash on and off in predetermined sequences. A special camera, which detects only diode-generated light pulses, automatically registers the coordinates where the light strikes. The system easily determines the location of the point on the moving object from which the light initially came. These data go to a computer where the motions can be analyzed in detail.