Re: Viewing System of Choice (IMAX)

[P3D Andrew Woods <andrew@xxxxxxxxxxxxxxxxxxxxx>]

John W Roberts wrote:
> an old message
> [Andrew Woods, November 12, 1995] stated that the regular polarized system 
> doesn't work well on the domed screen of a SOLIDO theater, and I had the 
> impression that the LC shutter glasses are mainly used in SOLIDO theaters.

The explanation I received from Gordon Harris (Manager of Film Technology
at IMAX) was that polarisation doesn't work too well in the IMAX DOME
(OMNIMAX) theatres.  Therefore the LC shutter glasses must be used
to achieve 3D in the domed theatres (and this is called IMAX Solido).

In the IMAX theaters (huge flat screen), 3D can be achieved either by
polarising the left and right views and the viewers wearing polarising
glasses OR using the LC shutter glasses system.

The IMAX theatre in Vancouver Canada uses the passive polarising glasses
technique.  The IMAX theatre in New York uses the LC shutter glasses.

Gordon Harris also said that although the passive glasses are cheap,
they are easily damaged and easily stolen.  In contrast, the LC shutter
glasses are more expensive, but they last longer, are much harder to steal,
and also allow the installation of the small speakers (one over each
ear) for the PSE (Personal Sound Environment) system (which significantly
increases the reality of the sound field).

In one demo of the PSE, I was listening to a tennis match taking place 
somewhere in front of me and a voice kept on whispering over my shoulder.
Yes, I did look over my shoulder to see if someone was really there.  :-)

John R also wrote:
> I found that the high speed shutter setting on mine wasn't much use for
> 3D.

I get quite annoyed at the inappropriate use of the high speed shutter
setting of video cameras in supposedly professional broadcast/television
footage (usually sports).  The high speed shutter is really only useful 
if the footage is going to be analysed field-by-field for a slow motion 
replay.  In normal full motion playback, it just adds a certain jerkyness 
to fast motion.  For 3D, the same thing if not worse would occur.

It should be said, just to clear up any possible mis-understanding,
that the shutter speed setting of video cameras has nothing to do with
the field rate of the video camera.  The field rate will always be 
60Hz for NTSC or 50Hz for PAL (unless you have a non-standard video
camera)

With regards to the discussion of temporal sequencing of 3D images (at
the camera and the display).  Following John R's description of the IMAX
system, here is a similar description of the possibilities for 50/60Hz
Video.  Where: L1 L2 are fields 1 and 2 from the left camera, etc.

Left camera:    L1 L2 L3 L4 L5 L6 L7 L8 L9 
Right Camera:   R1 R2 R3 R4 R5 R6 R7 R8 R9

ALTERNATIVE 1:  L1 R1 L3 R3 L5 R5 L7 R7 L9
ALTERNATIVE 2:  L1 R2 L3 R4 L5 R6 L7 R8 L9
ALTERNATIVE 3:     R2 L2 R4 L4 R6 L6 R8 L8

ALTERNATIVE 2 is the system used by the Toshiba camera and all other
standard field-sequential 3D video systems that I know of.
Date: Sun, 12 Jan 1997 22:38:31 -0600
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ALTERNATIVE 1 is the system that John thinks would produce more realistic
motion.
ALTERNATIVE 3 is principally the same as ALTERNATIVE 1 except that
instead of the left fields being the dominant field, right fields are
the dominant field.

I personally believe that ALTERNATIVE 2 is the better system because the
display presents the stereoscopic images in the same temporal sequence 
as they were captured.

I guess at this point we should both run off and perform some real
experiments in our own laboratories - but that will have to wait.
Anyone know of some firm evidence.

Andrew Woods.


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