P3D More on 3D video projection

["Xal razutis" <razutis@xxxxxxxxxxx>]

No reason to convert slides to the lower-res. digital formats (Allan Wodds' 
post) when 3D slide projection technology is perfectly sufficient for the 
task.

No reason to complain about lower-res. video (or digital video) (Greg 
Wageman) when the basic arithmetic of photo resolution versus video 
resolution is part of the inherent differences between the two.

One could complain that 'photo 3D' is limited to static representations(!) 
whereas the motion-picture video standards have sacrificed image resolution 
for convenience of limited-bandwidth distribution.


A motion-picture image (let's use 16mm film as an example) requires less 
resolution (per frame) to convey the content (perceived detail).
Blow up single frames of 16mm or 35 mm film and see the grain 'difference' 
between what appears and what is.

Distribution via digital (and web) means is part of 'getting the message 
out'.  Purists may despise low resolution, as is their right, but unless one 
has access to their very own IMAX 3D theater, along with the large-format 
dual-projection systems, the argument of high and low resolution will never 
be resolved to the satisfaction of all.

For my purposes, 3D video is portable, mailable, presentable, and cheap (in 
comparison to film).  It is there to convey a very different content: motion 
in space and the aesthetics and kinaesthetics of that content.

Re: Phillips' question:

>
>What exactly is a de-mux box and how does it work?
>


Andrew Woods can provide a technical description of his de-multiplexer (and 
multiplexer) units, but basically, a field-sequential 3D tape signal (of any 
guage) is input via VCR into the de-mux box, and the left-eye image channel 
is separated from the right-eye image channel along with (what I assume) is 
line-doubling (filling in the missing odd or even lines).  The result - two 
video channels/signals - are fed to two video projectors which are aligned 
(superimposed) on a silver screen for FLICKERLESS viewing via standard 
polarizing glasses.

I've used both LCD projectors (eg. Sharp) and Barco high-end high-gain 
projectors.  Since the two channels are in sync and independent of each 
other (at projection) the latitutde of projector types and adjustments is 
wide.  Any pair of projectors that work in your teaching or presentation 
space will work here.

Silver screens are either assembled from Da-Lite material (6 foot wide rolls 
which can be sewn together and mounted) or made by using a silver-aluminum 
(acrylic) house paint.  The trick with paint is careful application, 
inspection under illumination by polarized light (to correct defects).  
Choice of paint varies.  I take a flashlight (with polarizer) and glasses 
into a paint store - a real 'eccentric' sight for fellow shoppers - and 
illuminate dry samples of the paint to determine 'efficiency' in reflecting 
polarized light.  Efficiency is pretty obvious when you look at the 
polarized reflection with glasses.  Some brands are better than others, some 
types of paint better than others, etc.

The Woods de-mux (de-multiplex) box  is by far the cheapest working model 
that I have found. It previously retailed for around $1 thousand US, as 
opposed to over 2500$ US for the Santa Barbara Nu-View company de-mux box, 
and even more from other suppliers (3DTV).

As distinct from the VREX single video-projectors, the two-projector system 
delivers (I think) superior 'resolution' and higher gain. There's nothing 
wrong with the VREX projector (I've given my take on their  horrible 
glasses) except that it is pricey and not adequate for large-screen (12 - 
15' diag.) public projections.

Except for extremely high-end models, LCD video/data projectors do not 
typically work for field-sequential tape as a stand-alone item (they are 
unable switch cleanly between fields due to inadequate rise/decay time of 
the LCD panels) if one was to use them as a single 'monitor' but as a pair 
(after de-mux) they are perfectly adequate.  There is no flicker to worry 
about, and no need for shutter glasses.

Al Razutis


Visual Alchemy
razutis@xxxxxxxxxxx
razutis@xxxxxxxxxxxxxxx
web: http://www.alchemists.com/
film-3D-video-holography-VRML


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