Re: 3D Video

[P3D Andrew Woods <andrew@xxxxxxxxxxxxxxxxxxxxx>]

jgore@xxxxxxxxxxx asked:
> What I want to know is if they are using the same technology that 
> 3DTV is using? If I buy one, can I use the tapes from the other 
> place?  Do they all use the same kind of tapes? I'd really like to 
> know before I give 
> 3DTV $145 for their 3D Theater package. 

There are three types of 3D Video tapes I have heard are on the market - 
they are (1) pulfrich (2) anaglyph and (3) field-seqential (uses LCD shutter
glasses).

The Best and most effective technique is number 3.  Full colour 3D images
albiet with some flicker.  
NTSC (or PAL) video consists of a sequence of 60 (or 50) images per
second.  These images are called fields.  field-sequential 3D video uses
alternate fields to display the left and right images of a 3D image.
i.e. LEFT-RIGHT-LEFT-RIGHT-.....
The image sequence is viewed through a pair of LCD shutter glasses.
When a left image is displayed on the screen the left shutter in the glasses
goes clear and the right shutter goes black - therefore only the left image
sees the left image.  The reverse happens when a right image is displayed.
Therefore the left eye sees 30 left images per second (25 for PAL)
and the right eye sees 30 right images per second (25 for PAL).
The reduction in the image frequency is the reason for the flicker.

The black box they refer to drives the LCD shutter glasses in synchronisation
with the images displayed on the TV.  Typically the black box plugs into
the video output of your VCR.  A small "plug pack" power supply provides
power for the black box.  The glasses then plug into the black box.

The only incompatability between field-sequential systems is that some
use the reverse image polarity.  That is, the tape is recorded as
RIGHT-LEFT-RIGHT-LEFT rather than LEFT-RIGHT-LEFT-RIGHT.  Some boxes
(e.g. the 3DTV box) have a polarity switch so that you can view box
polarities correctly.

To view Pulfrich and Anaglyph tapes you only need a cheap pair of 
cardboard glasses - therefore there is no extra cost on top of the video
tape for a special black box and glasses.   Therefore the tapes you mention
are unlikely to be the Pulfrich or Anaglyph formats.

> Also, I have a pair of shutter glasses for my computer which I use to 
> play Descent-2. I have to stop about every 30 minutes or I feel a 
> strain in my eyes. Some programs allow changing all the 3D parameters
> so it matches your eyesight better. I'm assuming you have no control 
> at all with 3D videos. Does anyone have the 3D Theater from 3DTV?
> Does it hurt your eyes to watch it for long? Is it worth the $145 ?
> 
> Any information on 3D video would be apreciated........

The only control you have with 3D video tapes is the size of your TV and
if you only have one TV you don't have much control...  :-)

Truly, 3D video tapes can be done well and then they can be done badly 
(very badly in some instances).  The two killers are vertical parallax
and excessive horizontal parallax - as with other forms of 3D.
Ideally vertical parallax (vertical separation between common points)
should be zero.  Horizontal parallax is what gives the 3D image the
3D.  Everyone's limit of horizontal parallax is different and also
depends upon screen size and viewing distance.
So in short, fatigue will depend upon the actual video tape.

Generation of 3D video is usually done with a pair of genlocked video 
cameras and a 3D multiplexer.  The multiplexer receives the input of the
two video cameras and outputs a field-sequential 3D video signal.  It is
basically just a very fast switch which selects odd fields from one
camera and even fields from the other camera.  The output can then be
recorded on a standard VCR or viewed directly on a monitor.

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