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From: cwr%SCH-Gila@sri-unix.UUCP
Newsgroups: net.sf-lovers
Subject: high frame rates / strobing
Message-ID: <12408@sri-arpa.UUCP>
Date: Fri, 6-Apr-84 21:20:00 EST
Article-I.D.: sri-arpa.12408
Posted: Fri Apr  6 21:20:00 1984
Date-Received: Sun, 22-Apr-84 09:30:51 EST
Lines: 30

From:  Craig W. Reynolds <cwr at SCH-Gila>

    Date: 1 Apr 84 21:36:54-PST (Sun)
    From: hplabs!tektronix!uw-beaver!cornell!vax135!floyd!clyde!watmath!wa
    From: tcgl!dmmartindale @ Ucb-Vax
    Subject: Re: high-speed film
    ... With 60 frames/sec, motion would be a lot smoother.  Does it use
    a single-blade shutter in the projector?  That would get rid of the
    double-image effects seen when something moves rapidly.

I think Showscan uses a single bladed shutter.  The 60 hertz frame rate
does make the motion look better, higher sampling rates allows higher
frequencies in the motion with less noticable strobing.  On the other
hand, higher frame rates do not make the problem (temporal aliasing) go
away, any more than using more pixels (higher resolution) on a display
screen makes the "jaggies" (spatial aliasing) go away.  It merely
reduces the amplitude of the error.

BTW: the correct solution to the strobing problem is to use "long" (on
the order of a frame time) "time exposures" to allow the image to
integrate, to properly blur on the film.  Unfortunatly for real cinema-
tographers, this means that the camera must do its close-shutter/pull-
down-film/open-shutter cycle in zero time (a mechanical impossibility).
And in fact, preferably the exposure periods of two sequential frames
would overlap to some extent (sort of a "cross dissolve") which -- since
the camera has only one frame behind the lens at a time -- is a logical
impossiblity.

Luckily, this is not a problem for people who make movies by computer
simulation...