From: rick@tekig1.PEN.TEK.COM (Fredrick Wilson)
Newsgroups: alt.3d
Subject: Re: How do I generate the two views for a 3d image (LCD glasses)
Date: 1 Sep 92 01:09:27 GMT
Organization: Tektronix, Inc., Beaverton,  OR.

>In article <BtpExz.4t3@ie.utoronto.ca> drascic@ie.utoronto.ca (SpIke) writes:


>What you mean by "stereo window" is not clear.  There certainly is no
>standard terminology for such things.  I would appreciate a definition.

By "stereo window" I mean something very similar to your "Display Surface."
I think of it as a window in a wall.  Objects are viewed through this
window.  The objects can be well behind the window, at the window,
or protruding through the window toward the viewer.  Objects in front
of the window should never have their edges cut by the window.

I have seen "window" refered to like this in books and at an NSA convention.

I set my window by deciding what object in the picture I want to
have AT the window.  Usually it is the nearest object, usually
it is at the bottom.  Sometimes I want something to come through
the window at me so I pick something behind that object.  I then
crop the left and right edges of both the left and right views so 
the selected object is the same distance from the edges in both views.
(Both views are now the same width, too.)
The stereo window is now set.

Parallel-view photos have a little extra on the left side of the left view,
and a little extra on the right side of the right view.  This techique takes
those off and gives the window a very sharp, realistic appearance.

>I'd also appreciate whether you are speaking about photographic, computer
>graphics, video, or all three.  You've made no distinctions that I could
>see.

Most of my experience is with single-lense photography.  Some with 
computer graphics.  The concepts should apply to all forms.  If I 
take a photo of a video, and then digitize the photo, and add 
digital graphics to it, it's all the same.


> and experiments
>conducted here at the University of Toronto and elsewhere have shown that
>properly designed converged camera setups can produce an image that is
>highly pleasing to the viewer, even for long periods of time.

Yes, if the convegence angle is small (less than a few degrees), and
the subject is appropriate.  I took converged photos for about a year,
wondering why some worked and some didn't.  Then I took one of a 
water faucet on the side of a house.  The straight lines in the siding
on the house were impossible to view properly, and painful to try to view.
That convinced my to take parallel pictures and let my eyes do all the
converging.


>>Convergence error can be compensated for to some extent by rotating
>>the images (and cropping again) but you can only fix part of
>>the picture at a time.  You can't fix the whole picture at once without
>>fancy image processing.
>
>This will work for computer graphics, but not for video.

It works for photography too, but it's better to take the originals
so they don't have to be rotated.  I agree that rotating your
swiched video views on a monitor would be a royal pain.  We probably
make something here at Tek in either the TV group or the stereoscopic
monitor group that is capable of it, but I'm sure most people would
rather not have to use it.


>>You have a choice.  Good stereo with a little of the edge cropped off,
>>or painful convergence error.  I used to do the latter, now I do the
>>former because it's more pleasing to view.
>
>"Painful"?  Hmm.  All blanket statements are incorrect, including this one.

If I had a scanner I could show you what I mean with the faucet photo.
It HURTS to look at that sucker.  Less convergence would be less
painful, but would also have less stereo effect.  To get the same
amount of stereo effect back it would take seperating the cameras
in a parallel fashion.


>>The effects of the "convergence error" can be controlled by choosing your
>>camera separation and field of view (i.e. focal length).  
>
>>BTW, I don't mean to be confrontational.  I'm just trying to help you
>>understand what I think you are missing.
>
>Your last paragraph IS confrontational, I'm afraid.  Personally, I find I
>learn a lot more from people who are trying to state their own case clearly.

I'm sorry if I wan't clear enough.  The original question was: Should
I use method 1 or 2 or 3?  I said that method 2 was best because you
don't have to "control" your "convergence error" because there is none.
I didn't expect anyone to argue the merits of method 3.




      Rick   Wilson             Rick Wilson       Cross-eyed STEREO
      --------------           --------------
     |       O      |         |      O       |
     |    O         |         |     O        |    rick@sable.pen.tek.com
     |              |         |              |    Tektronix
     \    _     O   |         |\    _  O     |    Beaverton, Orygun
     |\  /      _   |         | \  /   _     |
     | \/   \  /    |         |  \/\  /      | 
      --------------           --------------      
Newsgroups: alt.3d