Magazine article American Cinematographer

TIME CODE ON FILM: Kodak's Transparent Magnetic Coating for Film

Magazine article American Cinematographer

TIME CODE ON FILM: Kodak's Transparent Magnetic Coating for Film

Article excerpt

Kodak recently announced a development which may have a revolutionary impact on the use of motion picture film. They have devised a method whereby it is possible to coat the base of the film with a transparent magnetic coating which can be used for recording time code. What this means is that motion picture film can be "frame addressable" by computer, i.e. a computer can read transport device with absolute frame accuracy.

The implications of this development are far reaching and may have a significant impact on the current trend towards the use of videotape as a production medium instead of film. Kodak has not actually started manufacturing film with the magnetic coating on it, but they have demonstrated that they can do it if there is a sufficient demand for it. They are now hoping that equipment manufacturers will design the components necessary to take advantage of the technique.

The coating consists of iron oxide particles (gamma ferric oxide) dispersed in a cellulose acetate similar to the base of the film. It is less than 8 microns (or .2 mils) thick and is applied over the entire surface of the base side of the film during the manufacturing process. Because the coating is a cellulose acetate there would be no problem with chipping or cracking or peeling off the base of the film. The iron oxide particles themselves are Vi micron long and 1/1 Oth micron wide and there are approximately 9 billion of them per square inch. Since the coating is on the base side of the film, it has no effect whatsoever on the exposure of the film. It does add transmission density of less than 0.15 to the film however which must be compensated for in printing. In essence the coating acts as a very light neutral density filter in printing or projecting.

The coating is essentially the same as the iron oxide coating used in magnetic recording tape except that it is in a transparent binder and the density of the particles is low enough to make the oxide transparent. It responds to magnetic fields in the same way as conventional magnetic tape but because of its much lower density its output is approximately 56 db lower than magnetic tape. This means that it can record digital data or an audio signal with a fidelity comparable to that of a telephone. It is not designed to record a sound track, but it could conceivably be used for voice cues of some sort. Anything recorded on it can be erased just like a recording on magnetic tape.

There are two ways in which data could be recorded on the track. With a 75-mil record/playback head in contact with the coating, it can record more than 266 bits of data per inch or at least 100 bits per frame on a track outside the picture area. This is well in excess of the amount of data required for an 8 digit SMPTE time code number for each frame of either 16mm or 35mm film. secondly it would be possible to record and play back a similar amount of data without having the head touch the surface if the entire width of the film were used for recording.

NO CLAPSTICK

The ability to record time code on film as it is being exposed in the camera would, first of all, eliminate the need for clapsticks. If a time code generator were feeding time code to the camera and the audio recorder simultaneously, there would be a running sync reference throughout every scene. …

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