P3D Re: eidetic and Pulfrich?

[wier@xxxxxxxxxxxxxxxxx (Bob Wier)]

>The problem with thinking of it as a memory model is that you could watch a
>30-minute movie with continuous Pulfrich effect, and see stereo the whole
>time. For the view from the eye with the dark lens, you would have to be
>"storing" the view all that time without consciously seeing it, then
>"recalling" it a fraction of a second later.
>
  Ah yes - there is some ambiguity there with regard to the editker results.
I was making some assumptions based on the article (bad move, probably)
that in adults, the visual playback capability would be limited in time
- much like persistance of vision, but from a different source. Thus
when the movement stopped, the projection effect would still be operating,
but with static images, the stereo effect would drop out.

One thing which wasn't mentioned in the article would be whether in non-RDS
situations if the eidtic memory still functioned in stereo. That is,
whether people could project and explore stored images in stereo (assuming
they had originally viewed it that way) as opposed to flats..

(Tangent - do people *dream* in stereo? I'm *pretty* sure I do, but am
not 100% - I know for sure I dream in color)

>model. One of the important issues in an electronic design is "skew" - the
>relative timing (or delay) among two or more signals. If you have two signal
>paths with intermediate stages, with identical logical design, but one path
>is built using (for instance) 74S series logic, and the other with 74LS
>series logic, then the signals along the path using the 74LS logic will arrive
>at the destination significantly later than the signals on the 74S logic

One of the exam questions from my digital logic classes I taught in
Arizona: - Why would you want to put two NOT gates in series when they
cancel each other out? Answer: they cancel each other logically, but
can be used to equalize skew with other multiple level gate logic
in the system to prevent glitches and race conditions - it's amazing
how many students didn't seem to catch that...

The visual skew question is pretty interesting. I believe that some animal
visual systems are optimized to detect movement, but are relatively
insensitive to static scenes. Having different skew rates between the
images of the lighter/ darker lenses might well be very significant. And of
course leading edge and trailing edge skew might both be involved (since
the afterimage of a bright scene persists longer than that of a dimmer
scene). It might also have some ramifications as to why some of the
pulfrich stuff back in the spring (3rd rock) worked pretty well, and other
did not. The 60 frames/second scan of NTSC might give you a pretty narrow
"window" (to coin a phrase :-) where the P effect would work well (vis a
vis contrast/brightness/hue/saturation) given the necessity to match up
with the average human stereo perception system.

(Another Tangent question - did anyone/everyone get their copy of the 3rd
Rock tape - did it look better/worse/same on tape vs over the air?)

>
>Pulfrich question: if you make a traditional 3D movie with polarized or LCS
>glasses (instead of Pulfrich glasses), but display one view much darker than
>the other one, does the Pulfrich effect still work? It seems to me it would,
>but it would be interesting to hear whether it's actually been tried. If
>it does work, it would be interesting to find out what happens when 2-camera
>stereo and the Pulfrich effect are used *in combination*.
>
>John R

Yet Another tangent -

As I've mentioned here before, some years ago after I got ahold of a
pair of the SEGA glasses, I did some experimenting with switching rates
on the LCS panels. In order to determine how fast I could run them, I
fed the output of an audio square wave generator to one side, and fed
the the other side thru a NOT gate. Looking at a display of the wave
on a scope was interesting. The glasses would block various parts
of the waveform as they turned on/off. The turn on skew was pretty bad -
I would not see the rising edge hardly at all. As the trace proceeded to
the right, it would gradually fade in and I'd see the trailing edge just
fine. But of course, I'd be missing the leading edge on the other eye.
So it occurred to me that when looking at the turn on/turn off waveform,
you'd need to run it at several multiples of the actual switch rate (this
is in addition to the MUCH higher oscillator freq required). You'd
probably want to overlap the turn off of one eye and the turn on of the
other eye by some amount determined by the switch speed of your LCS
(particularly given that the "game quality" LCS have relatively slow
switch speeds). You'd not want to overlap so much that you got lots
of ghosting,though.

I know that some people who are deeply involved in this type of design
read the list, but they might not be able to comment :-)

THANKS

   ====== wier@xxxxxxxxxxxxxxxxx ======
  1:19 PM Friday, December 26, 1997
   keeper of the Photo-3d and Overland-Trails
       mailing lists and other stuff
     (currently in Ouray, Colorado)



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