[opendtv] Re: The Plain Geometry of Stereoscopic 3D

  • From: Mark Schubin <tvmark@xxxxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Tue, 09 Mar 2010 12:04:31 -0500


On 3/9/2010 11:09 AM, Manfredi, Albert E wrote:
Mark Schubin wrote:
Next comes screen size. In a movie theater, it is possible to adjust
the IPD for the screen size, either to a desired mean or, perhaps,
to a maximum, so that no viewer needs to diverge (an unnatural eye
movement), no matter how distant the object displayed.

In theory, at least, the same could be done in a TV set. "Knowing"
its screen size, a processor could adjust the 3D accordingly. I am
not aware, however, of any TV set doing so. So, if a broadcaster
transmits one signal that might be displayed on screens ranging
from a 1-inch mobile phone to a 152-inch plasma, the IPD will vary
accordingly, outside the control of the broadcaster.
I don't get how 3D TV can work WITHOUT such a scheme.
Well, on behalf of the 3DTV proponents, if you choose an IPD for the largest screen, then no one will have to diverge on any screen size. If you choose an IPD for a movie screen, then uncorrected cinema material on any size TV screen will not cause divergence. There might be a giant's eyes effect, but (depending on viewing distance), one of the strongest human visual depth cues is stereopsis (the different views for the left and right eyes), and those are created in shooting, not display. The muscular convergence might not indicate the desired depth, but the stereopsis will. Whether that cue conflict will cause discomfort, as the accommodation-convergence conflict does, remains to be seen.


I also don't understand how one can create the effect of focusing on infinity, when the 
eyes are essentially parallel, when viewing the image on a 1" screen. Maybe I'm 
missing something, but doesn't the screen have to be wider than the 2.5" IPD, to 
create the two images at all possible ranges?
Same issue, smaller screen: the stereopsis (created in shooting) can come through; the convergence can't.

Personally, I find 3D on tiny mobile screens reminiscent of children's plastic rulers with lenticular 3D scenes on them.

TTFN,
Mark



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