Xref: utzoo comp.graphics:6891 rec.video:7529
Path: utzoo!utgpu!watmath!att!tut.cis.ohio-state.edu!ucbvax!agate!apple!well!nagle
From: nagle@well.UUCP (John Nagle)
Newsgroups: comp.graphics,rec.video
Subject: Frame rate (was: Re: HDTV and ATV Glossary (TN32))
Keywords: frame Showscan video
Message-ID: <13130@well.UUCP>
Date: 14 Aug 89 16:24:45 GMT
References: <120919@sun.Eng.Sun.COM> <121076@sun.Eng.Sun.COM> <12027@ulysses.homer.nj.att.com>
Reply-To: nagle@well.UUCP (John Nagle)
Lines: 27

In article <12027@ulysses.homer.nj.att.com> ggs@ulysses.homer.nj.att.com 
(Griff Smith) complains about TV frame rates.  This is a significant point.
The Showscan film work indicates that humans notice an improvement in 
motion representation as frame rates are increased above 24FPS, and that
humans cease to notice an improvement somewhere between 60FPS and 80FPS.
In Showscan, frame rates in the 60-80 range are combined with 70mm film
and a wide screen to provide what might be called "improved definition film."
The various HDTV systems use frame rates well below this threshold, and it
may turn out that a second round of HDTV improvement will be necessary
at some later date.

Even "large screen" television, though, tends to occupy only a small percentage
of the visual field.  Showscan does attempt to provide a screen large enough
to fill the visual field, given a stationary head position.  Motion strobing
effects are most noticeable near the edge of the visual field, where the
motion-detection functions of peripheral vision dominate.  So the proposed
HDTV standards will probably be good enough for the small screen.

What they won't be good enough for, though, are video goggles.  Video goggles,
as used by the virtual reality types, attempt to fill the entire visual
field.  When the wearer turns their head, the image must pan accordingly.
That panning operation should not generate visible artifacts.  We can thus
expect that virtual reality systems will require frame rates in the Showscan
range before the wearer is comfortable moving at high speed in the virtual
environment.

					John Nagle