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.