Jose's in front/behind questions

[T3D Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Mon, 16 Dec 1996 17:48:35 -0800
>From: T3D Jose comments:
>
>>Jose':  >And that the scene will also never be seen in full depth.
>> 
>> Larry:  What is meant by *full depth*? I'm acquainted with stereo
>> scenes and consider that I've seen the *full depth* but I think I don't
>> understand your reference here.
>> 
>
>Jose: I meant full depth as seing in the same scene, simultaneously,
>images as close to you as your accomodation allows, and as far as the
>horizont [minimum   8-)].
>We know there is a circle whose radius put a limit on the distance
>between corresponding points in a stereo pair.  This is not a problem in
>a natural scene because the observer's eyes converges toward the object
>being focused, discarding also the presence of double images in front or
>behind.    

************  It is important to realize that the 3D experience is a
strongly relativistic one. There is another circle that is important and
that is the circle of one's attention within an image (variable). Images
tend to be somewhat abstract and as such don't convey a full scene in any
case due to field of view etc. The actual scale of depth in a stereo image
is flexible depending on whether or not it was photographed with infinity in
the scene, and how close the closest objects are. If the edge of the scene
were not there, you could indeed have the *full* range as you defined it. It
only requires that the closest aspects are themselves surrounded by areas
that are within a resolvable distance by comparison. Typically it is
difficult to have what you are calling a full range of depth because of the
need for corresponding transitional areas, all limited by the edge of the
image. 

It is also possible to enhance the depth factors by the use of computers.
For example a scene with a person fairly close and the background is the
horizon in the distance. Due to camera optics and such, the scene tends to
flatten out towards infinity. The personal reality in the scene is more
likely to seem deeper to the direct senses because they are compiled from
more information. This is from either moving one's head or walking slowly.
This provides a sense of infinity going off forever instead of ending in a
flat wall. It is possible to take such a photo and stretch the infinity
factors relative to the closer elements and create more of a sense of
infinity in the more distant parts of the image. This is as close to *full*
as seems possible with photos. And one must keep these adjustments within
the physical reach of the viewer.

>.................snip...........................
>
>Jose': I am "crossed viewer", visited some of your figures, but they
>come very slow to me.  I do not know why crossed viewing can not allow
>images behind, parallel in front, but my aim is related to classical 3D
>cinematography, although I am interested also in the present techniques.
>The latter must in the end give the same result, I think.
>Seems to me that it is not possible one subject being well in front of
>the scene, while other goes very far behind, and the observer can choose
>which one of both to see.

************  It is because of crossover of the eye paths. Crossed viewing
puts the center of depth for a scene in front of the screen because that is
where both eyes see corresponding parts of the image. Parallel viewing does
the same thing but definitely behind the scene. With a different
presentation format, the scene can be centered depthwise on the actual
screen so that the image takes place both in front of and behind the screen.
This is true with anaglyphic views, interlaced views, projected polarized
views and some stereogram type views. It also has to do with placement of
the stereo window. My multi-dmensional stereograms exist both in front of
and behind the screen as well as passing through the actual screen. It
requires an understanding of the image format and the learning of precise
control with the eyes so as to actually follow the coincidence of pattern
through this full range. The reason other images don't do such a thing is
that it's difficult to follow and each stereo image has it's own range of
relative depth. This is still a rather full range.

One of these days I will animate my MDS Pyramids so that some kind of color
cueing allows the viewer to be taken on a tour through all available levels
in them. In reality they contain coincident levels that go outside the
limits of physical movement of the eyes. I have used optical devices to
resolve these deeper layers. In practice one travels through as much of it
as can be seen within one's own personal range of eye movement and
coordination. If you haven't explored this in my pyramids before, the
difficult challenge is to be able to resolve the stereogram 3D structure all
the way to the screen. Since the eyes want to jump to the more readily
available 2D screen image, this last bit of pattern closest to the screen is
the most difficult but is attainable with practice. The deeper parts are a
function of your own eye's ability to go beyond parallel or to go ultra-crossed.

The fact that I exploited in these pyramids was that any pattern that exists
in parallel space has it's correlation in crossed space too. By providing an
image that is contiguous with the screen I provide a bridge for the two
modes to be combined in the one image. Relatively few have been able to
realize that this exists without being specifically told and painstakingly
directed on how to tour the full image. It seems most appropriate to your
question to point you to this type of image. There are two of them at the
URL below:

        http://3dzine.simplenet.com/3dwebscp/sgallery.html

Questions to ask yourself while viewing:

1. What level am I viewing? Count upwards as you go into the parallel areas
behind the screen. Consider the screen as 0. A level is perhaps defined as
the center depth for a particular central area to be in-focus.

2. Which level is easiest for me to access first? Is it level 2 or 3 or 4?

3. Which area is easiest overall, in front of the screen or behind the screen?

4. At which level is the ordinary pyramid manifest? (In parallel this is a
Top view as if you are an eagle flying directly over the pyramid.)

5. Can you converge the patterns all the tenuous way to the screen? This
requires the eyes to move very slowly, staying locked on each level of
continuous coincident patterns. Typically your eyes will jump from one layer
to another. There is coincident content at all levels in an infinitely
continuous flow with physical limits of eye movement the only outer limit.
You may at times have to jump over a void to get to the next *ramp-like* bit
of image, but the jump has both ends at identical depth levels.

6. How many levels exist between the ordinary pyramid and the screen surface?

7.  Can you see which levels have a surface that is itself structured in 3D
as opposed to a flat and smooth surface? (The two examples differ in this
regard.)

8.  How many levels deeper than the pyramid can your perception travel? If
you are having difficulty getting deeper than this, a hint: travel to the
base of the pyramid and hold onto it while picking up the tip of the next
level which will form in the center of the image given the time for your
eyes and mind to allow it. Think deeper, deeper...

9.  When in a deep level and holding, how many separate layer's edges can be
identified by allowing your perception to widen to the whole screen while
maintaining the same depth of focus? (even if it's accomadation to the eye,
it's focus for the mind) How wide can you go?

10. (Ultra Advanced) Can you notice the *edges* of your own perception as
the mind adjusts to the continuous flow of inter-relationship presented by
the eyes as you explore up and down the depths? You are constantly seeing
the same patterns except their relationship keeps changing. There is a
definite edge to the point at which your mind maps a pattern to one level or
another due to relativistic image processing in the mind's own processor.
This is the only exercise I know of that permits this glance at one's own
mind at work doing that which is usually considered unreachable and automatic.

Hints:

***  Learn to scan your eyes smoothly from the center to the edges at the
top or bottom and back again.

***  Learn to hold your view on one object point and to allow your awareness
to expand over the surfaces and depths available from that point. You will
find that you can *will* your DOF to change and hold the same central focus
point. Eventually you can smoothly slide your perception up and down the
ramps as if you were in physical contact with the surfaces. By that time
your stereo acuity is getting better due to precisely strengthened and tuned
eye muscles.

***  Stop and take a break any time you feel stress or tiredness. It may
take repeated attempts over time before you can accomplish all of the above.
_______________________________
>> Larry:   ....  Then the laser
>> scanning systems that project the image directly into the eye will have a
>> good chance to exceed whatever lenticulars may accomplish.
>
>Which system is that?. Please give me a reference.

*********  It was discussed recently on P3D and  Jacques Lajoie
<lajoie.jacques@xxxxxxx> provided the links.

http://www.hitl.washington.edu/projects/vrd/project.html

There is also a photography of a projecting vrd at:
http://www.nari.ee.ethz.ch/nari_lectures/bildkom/Studenten_Projekte/Sommer95=
/Projekt7/vrd.html

Someone else provided this link:
I think there's a link into another Washington site:
http://www.hitl.washington.edu/projects/vrd/sid-vrd.html

***  All very interesting...

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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

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