RE: 3D SPEX (and LCS in general)

[P3D Greg Marshall <greg.marshall@xxxxxxxxxxxxxxx>]

John Urbanic wrote:

>I haven't had the chance to keep up in this forum as much as I would like,
>but if Greg Marchall's otherwise well-informed reply (sounds like he's been
>around awhile) reflects the current conventional wisdom in this group, I
>have a pleasant surprise.  Greg stated the rather overlooked fact that:
<snip>
>NO, NO, NO!  You can look at my companies "3D Theory" section on our Web
>pages (www.neotek.com), but basically, as Greg noted, you can get just about
>any monitor to go to 120Hz if you keep the total bandwidth (i.e. resolution)
>the same.  This is the basis of the system that we have been selling to
schools
>(Universities, Colleges and now High Schools) for years.  You CAN NOT get a
>high-quality display if it flickers, and it will flicker in a normal room on
a
>normal monitor if it is not at least 120Hz
<snip>
>The way we do that is to include hardware which "synch-doubles" or adds an
>extra vertical refresh signal to the video cards signal.  This allows the
>monitor to refresh at twice the old rate without changing the bandwidth, or
>total resolution of the signal as delivered from the video card.
<snip>

Excuse me, I should have known John would jump on this opportunity to
extol the virtues of "sync-doubling".  But I'll repeat what I said
before:  Sync
doubling is no magical solution - you can describe it a few different
ways but
the bottom line is exactly what you said:  ...you keep the total
bandwidth
the same.  You don't want it the same - you want it to double (same b/w
for each eye).  In other words, sync-doubling gives you only half the
vertical
resolution. Now this is fine and very useful for some applications, but
it's no 
break-through technology.

>Greg also has some other astute insight:

>> (2) Stereo images on CRTs exhibit ghosting due to the
>> long exponential decay of the phosphors.  This can be solved
>> very easily by changing the phosphor composition.

>OR, and this is a big OR, reprocessing the image to mute the problem
>chromal boundries.  Actually, it is a little more complex than that as the
>real problem isn't the absolute phospher persistance, but the imbalance in
>persistance between phosphers.  By doing some image processing to mute
>this appropriatly (say a high parallax, vertical edge with a large contrast
>change on the worst chroma), this problem can be eliminated in all but
>pathological cases

Agreed.  I've done some testing of this technique with less than
spectacular results, but I haven't had that much time to work on it.
I'm
sure you have done much better.  Of course, it detracts from the
overall dynamic range of the image and requires considerable
processing for each image.  How well does your technique work with
varying phosphors?  I've encountered quite a range in differential
decay rates on various monitors.

>> CRTs will eventually be replaced by various flat panel displays
>> which (guess what?) are even more problematic for stereo!

>If these were LCD's you would be right, but the future at this point seems
>to be all Digital Micro Mirror (the Texas Instruments technology that has
>quickly begun to dominate the projection market; it is used by most of the
>major Japenese vendors) which is even more stereo-friendly than CRT's.  It
>is a great time to be doing high-quality stereo work!

>John Urbanic

Good point, I'd forgotten about DMM.  This is important because this
technology will probably replace commercial film projectors.  However,
considerable advancement and cost reduction is needed before it can
be used for "personal" displays.  These devices already use an enormous
amount of bandwidth to modulate intensity via time division - doubling
that to provide stereo would undoubtedly cause some TI engineers to
pull their hair out in frustration!

The likely candidate for future TV displays is fluorescent, which I have
to admit I know nothing about.  But I suspect it has similar b/w
limitations.

Greg Marshall



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