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Path: utzoo!watmath!watcgl!dmmartindale
From: dmmartindale@watcgl.UUCP (Dave Martindale)
Newsgroups: net.video
Subject: Re: converting film to video
Message-ID: <2432@watcgl.UUCP>
Date: Sun, 15-Apr-84 13:58:20 EST
Article-I.D.: watcgl.2432
Posted: Sun Apr 15 13:58:20 1984
Date-Received: Sun, 15-Apr-84 23:37:28 EST
References: <299@vortex.UUCP>
Organization: U of Waterloo, Ontario
Lines: 23

The film chains which transfer film to NTSC video do not usually show
some frames once and some twice.  NTSC uses 30 frames per second, but
60 fields per second.  The film chain will hold one frame of the film
in position for 2 fields (=1 TV frame) and then hold the next film
frame in position for 3 fields (=1.5 TV frame).  The net result is
24 film frames/sec matches 60 TV fields/sec, while the motion isn't
much disrupted.

However, any home videotape that I've seen which started out as a film
seems to have every 4th film frame recorded on two successive TV frames,
with one TV frame for each of the other 3 film frames.  This gives
a frame rate match again, but I would expect the motion to be less
smooth since some frames are held for twice as long as others, compared
with the 3:2 ratio of the system described above.  I couldn't see any
problem at full speed, though.  Anyone know why this system is used?
The only thing I can think of is that in stop-frame operation, each
TV frame comes from a single film frame and so would be a stable image.
Using the 2:3 method causes 2 of every 5 TV frames to be made up of
two fields which came from different film frames - these would have
very pronounced flicker or jitter if displayed in stop-frame.

The Europeans have none of these problems, since they use 25 frames/sec
for both film and video.