Re: Broadcast SL3D

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Sat, 24 May 1997 20:42:47 -0500
>From: P3D William Carter  <wc@xxxxxxxxxxxx>
>Subject: Re: Broadcast SL3D

>John Roberts asks:

>>How could an observer without shutter glasses fail to notice a flickering
>>effect?

>The easy answer is, since one viewable image is carried on one set of scan
>lines, and another viewable image is carried on the other set, and, since
>the two sets composite into a standard 2-D flattie, you wouldn't be any more
>likely to get flicker than you'd normally expect to find on the trailing
>edge of some moving object. 

>The real world answer is, in the early days of my video SL3D, I was getting
>some flicker. It would be noticeable where I had allot of contrast, like
>with lens flare. I think I corrected those problems by improving the sync.
>Kind a like you may see with titles on the "big screen", where the shutter
>and pull-down are a little off and you get smear. But, I've also been
>running at 120 Hz for quite awhile now.

OK, so the 120 Hz would account for the lack of flicker. If by "smear" you
mean horizontal ghosting, it sounds like that's where the 3D information is
encoded - in high-contrast high-displacement situations, if you ran it at
60 Hz interlace (30 Hz frame rate) and viewed it without shutter glasses, it
would appear to flicker.

Thought experiment - if you use sequential-field SL3D to display a collection 
Received: by bobcat.etsu.edu; id AA21735; Mon, 26 May 1997 23:08:29 -0500
Date: Mon, 26 May 1997 23:08:29 -0500
Message-Id: <3.0.1.32.19970526235909.006a6b84@xxxxxxxxxxxxxxx>
Errors-To: 3d-moderators@xxxxxxxxxxxxxxx
Reply-To: photo-3d@xxxxxxxxxxxxxxx
Originator: photo-3d@xxxxxxxxxxxxxxx
Sender: photo-3d@xxxxxxxxxxxxxxx
Precedence: bulk
From: photo-3d@xxxxxxxxxxxxxxx
To: Multiple recipients of list <photo-3d@xxxxxxxxxxxxxxx>
Subject: PHOTO-3D digest 2079
X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
X-Comment:   The Stereoscopic Image (Photo-3D) Mailing List  
Status:   

of white squares, sides vertical with respect to the screen, some far away and
some much closer to the lens, with a black background, and the depth/aperture
adjusted so that with shutter glasses you can perceive the distances of the
squares more or less accurately, then if you try to view the screen *without*
the shutter glasses, some or all of the white squares will appear to be
stretched out horizontally into rectangles, the absolute amount of stretch
on the screen being a function of the distance of the white squares from the
lens, or else the white squares will exhibit a horizontal ghosting effect,
and/or some degree of flicker. At 120 Hz I would expect the ghosting to
predominate for this high-contrast scene, though if there's not a pattern
in the background it might just appear that the squares are stretched out
horizontally.

As you mentioned, it may be possible to choose situations (lower contrast,
etc.) where this effect would not be so noticeable. But then for broadcast
TV, you have the same problem the anaglyph and Pulfrich guys traditionally
have - persuading the people making the show to use the effects correctly.
The minute you tell them to avoid vertical lines with sharp contrast, they'll
rush out and start making plans to depict the Parthenon lit up at night. :-)

I've never seen SL3D photographs - the discussions on P3D make it sound
like they may be very worthwhile for many situations. I'm willing to allow
that a video version with shutter glasses may produce very nice effects,
but I strongly suspect that under actual NTSC broadcast conditions, it will
be likely to produce very noticeable artifacts when viewed *without* the
glasses. In other words, sequential field SL3D video may be great for
people who have the receiving equipment, but I'm still skeptical of the 
ability to broadcast it over the airwaves and expect nobody to notice. :-)

John R


------------------------------