A DEVICE FOR SYNCHRONIZING BIOMECHANICAL DATA WITH CINE FILM

Biomechanists are faced with two problems in synchronizing continuous physiological data to discrete, frame-based kinematic data from films. First, the accuracy of most synchronization techniques is good only t o one frame and hence depends on framing rate. Second, even if perfect ly correlated at the beginning of a 'take', the film and physiological data may become progressively desynchronized as the 'take' proceeds. A system is described, which provides synchronization between cine fil m and continuous physiological data with an accuracy of +/-0.2 ms, ind ependent of framing rate and the duration of the film 'take'. Shutter pulses from the camera were output to a computer recording system wher e they were recorded and counted, and to a digital device which counte d the pulses and illuminated the count on the bank of LEDs which was f ilmed with the subject. Synchronization was performed by using the ris ing edge of the shutter pulse and by comparing the frame number imprin ted on the film to the frame number recorded by the computer system. I n addition to providing highly accurate synchronization over long film 'takes', this system provides several other advantages. First, having frame numbers imprinted both on the film and computer record greatly facilitates analysis. Second, the LEDs were designed to show the 'take number' while the camera is coming up to speed, thereby avoiding the use of cue cards which may disturb the animal. Finally, use of this de vice results in considerable savings in film.