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From: cplai@daisy.UUCP (Chung-Pang Lai)
Newsgroups: comp.windows.misc,comp.sys.next,comp.sys.mac,alt.cyberpunk
Subject: Re: 3D display (Was: replacing the desktop metaphor)
Message-ID: <2459@daisy.UUCP>
Date: 17 Jan 89 19:51:42 GMT
References: <4362@pitt.UUCP> <257@gloom.UUCP> <5486@boulder.Colorado.EDU> <47308@yale-celray.yale.UUCP> <3670@tekig5.PEN.TEK.COM>
Reply-To: cplai@daisy.UUCP (Chung-Pang Lai)
Organization: Daisy Systems Corp., Mountain View, Ca.
Lines: 70

In article <3670@tekig5.PEN.TEK.COM> danm@tekig5.PEN.TEK.COM (Daniel Milliron) writes:
]One known problem with 3-D displays that is noticed only by non-average
]people is that the images are created/recorded assuming a particular eye-
]spacing.  While my friends with average eye-spacing are impressed by 3-D
]movies, I see them out of focus because my eyes are set slightly farther
]apart than the norm (but not unattactively ;-), causing the left and right
]images to blend incorrectly.  I know of no existing technical fix for
]this phenomenon, but if, in the case of computer images, the 3-D image is
]computed dynamically, then the eye-spacing could simply be an adjustable
]parameter of the algorithm.
]

I think your problem can be corrected by choosing another sitting position.
You are out of luck if you have to look thru a binocular type 3-D viewer.
If you still have problem, then I think it is not related to your 
"eye-spacing".  It is something else that I will discuss below.

If you imagine how your brain is being deceived of the 3-D image, you may
understand what your problem was.

When the two versions of the same image (one for your left eye and the other 
for your right eye) are spaced such that the lines of sight to these images 
are parallel, your brain will perceive that the image comes from the 
infinitive.  When the lines of sight are converging, your brain will perceive 
that the image is close by.  When the lines of sight are diverging, your brain 
is confused.  

On the display, if the left image is on the left of the right image, the object 
is perceived at a distance farther than the screen.  If the left image is
on the right side of the right image, your eyes have to cross to blend the
images and hence perceived as closer than the screen.  For wider spaced eyes, 
the image should appear closer because the lines of sight are more converging.
You can compensate this by using the effect of perspective (distant objects 
appears smaller,) the same pair of close images appears less apart which causes
the lines of sight to cross less when you sit farther away.  Hence in a 3-D 
movie theater, the nearer you sit from the screen, the more exaggerated the 
3-D effect will be.  Of course, there is a limit.  For instance, just focus on 
your finger and bring it closer until you touch the tip of your nose.  Up to 
certain distance, your eyes fail to see clearly.  I usually sit at the back 
because I cannot bear the eye strain when the images appears too close to me.
Furthermore, for images that are farther than the screen (i.e. left image on
the left of the right image), sitting too close will force your lines of sight
to go diverging in some cases, which your brain cannot inteprete.  In either 
case, you should always stay back when viewing a 3-D image.  In fact, wider
eye space is more suitable for 3-D viewing.

Another mechanism that your brain used to tell the distance is how hard your
eye muscles focus your lens.  3-D movie cannot trick your brain on this.  The
projection is always focused on the screen.  Some people cannot decouple the
two mechanisms.  The lines of sight tells the brain that the image is at five
feet while the focusing tells the brain that it is at 60 feet or whatever the
screen distance is.  For some people, the eyes automatically converge or look
straight ahead based on the lens focusing.  When the focus is at the screen
distance, they have no way to converge their lines of sight to blend the 
two images at a much closer distance.  If staying further away does not solve
your problem with 3-D display, this is more likely the reason than your 
eye-spacing.  I am very good at decoupling these two mechanisms.  I know 
because in many occasions I found myself sharing at void space without 
focusing at any place. :-)

I think the best 3-D display should beam projection directly into the eye balls.
The computer can purposely projects the images in front or behind the retina,
so that your eyes are forced to focus the lens in addition to converging the
lines of sight.

-- 
.signature under construction ...

{cbosgd,fortune,hplabs,seismo!ihnp4,ucbvax!hpda}!nsc!daisy!cplai    C.P. Lai
Daisy Systems Corp, 700B Middlefield Road, Mtn View CA 94039.  (415)960-6961