Subject: Sega glasses tech info

From: "Sean Wall, x3736" <[email-masked]>
Date: Mon, 8 Mar 93 17:00:25 EST

Hello,

        I'm looking for anyone who has information on how LCD shutter
glasses (like the Sega glasses) operate.  I've got a good idea about
how they do, but since I'm putting this information in a technical
paper, I'd like some confirmation.  Any takers?

-Sean

([email-masked])

---

From: Mark Kenworthy <[email-masked]>
Date: Tue, 9 Mar 93 07:55:33 PDT

>paper, I'd like some confirmation.  Any takers?

Sean - I do not own any such glasses, but the principles are very
simple.  Each side of the glasses has an independent LCD shutter.  Note
that LCDs with no current applied are clear, and become opaque when
current is applied (actually, it may be visa-versa, but I think this is
correct).  The LCD shutters are just one large LCD cell, as opposed to,
for example, a LCD computer display, which has thousands of cells used
as pixels.  Current is applied alternately to one shutter then the other
so that only one eye can see the computer display at a time.  The
shutters are synchronized with the vertical retrace of the video
display.  So, every 60th of a second (assuming a 60hz video signal), the
shutter on one eye goes closed and the other goes open.  The display
device is swapping the displayed information every 60th of a second
also, presenting a scene computed from the viewpoint of the left eye
during one frame and the right eye's viewpoint the next frame.  With the
two independent viewpoints, the 3D effect is generated.  Since the
persistence of images in the retina/brain is a very long time (100ms -
200ms), the observer only notices a reduction in overall intensity, due
to the half duty cycle on each eye.

Other miscellaneous info:

The "switching" time for an LCD is about 5ms, so actually the LCDs need
to be turned on and off prior to the vertical interrupt to get the
switching to occur prior to the start of scanning the next frame.  I do
not have any references on this, but this should be easy to find.

If the eye did not have the long retina/brain persistence, our current
display technology (monitors) would not work at all.  The pixels on a
display only stay lit for around 200 microseconds (a few scan lines). 
The only reason we see a complete display is the persistence of the
scanned image in the retina/brain.

Papers on persistance of image:

D. Allen Allport
"Phenomenal Simultaneity and the Perceptual Movement Hypothesis"
Brit. J. of Psych., v59p395-406, '68

D. Allen Allport
"Temporal Summation and Phenomenal Simultaneity Experiments with the
Radius Display"
Quaterly J. of Exp. Psy, v22p686-701

Joyce E. Farrell, Geo Sperling, and M. Parel
"The Visible Persistence of Stimulation in Stroboscopic Motion"
Vision Research, v30p921-936, '90/6

Hope this helps!

	- Mark -

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| Mark Kenworthy       |    "It's always something"    |
| [email-masked]    |     Roseanna Roseannadanna    |
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