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Stereogram FAQ
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Stereogram FAQBrought to you by Stuart InglisGeneral Questions[1] What is a SIRDS/Stereogram/Hollusion/SIS?[2] Terminology [3] How do I see them? Everyone else can see them.... [4] Where can I buy the posters from? [5] How can I generate them myself? [6] Which books/papers should I read? [7] What is a SIRTS/Ascii-Stereogram [8] Where is most of the discussion about SIRDS? [9] Internet locations for material (lots of pictures!) [10] Stereogram History
Subject: [1] What is a SIRDS / Stereogram / Hollusion / SIS?Have you walked through a mall lately? These days, as you wander past most of the poster shops, there will be a large group of people staring at the same poster with surprisingly weird expressions on their faces. Some will be in the initial stages of denial or rejection---they will be concentrating, some slowly rocking their heads backwards and forwards, searching for an image that they have never seen before. Others will be grinning from ear to ear, pointing at the poster, chuckling with their friends that a member of their group hasn't seem them yet. "Come on Bill, come on!", they cry and as Bill gets increasingly more frustrated he concentrates harder and harder, until finally (if he's lucky) he sees a true 3D image, without the need for special glasses or equipment. These pictures are known as Single Image Random Dot Stereograms (SIRDS), or Single Image Stereograms (SIS) depending on whether the picture contains random dots as a base for the 3D effect, or a repetitive pattern. Unfortunately, each commercial company has labelled them differently. Shop owners generally don't know what you mean, unless you say "Hollusion" or one of the many other specific names.
Stereogram Mechanism-- Cristian Alb (luminita@poincare.mathappl.polymtl.ca)Disclaimer: All the opinions and ideas presented in this [article] are mine and are the result of my own reflections on the subject. Purpose: This document wants to provide an easy understanding of the mechanism of 3-D perception related to stereograms. Due to the fact that it is the result of genuine thinking, I hope that this document provides a more intuitive approach to the subject. What is a stereogram ? In this document I refer to stereogram (though, single image stereogram would be more correct) as being something like the image that follows:
/=-- Y+-z-/=-- Y+-z-/=-- Y+-z-/=-- Y+-z-/=-- Y+-z-/=-- Y+-z-/=-- Y+-z-/=-- Y+-z *wm @m@w *wm @m@w *wm @m@w *wm @m@w *wm @m@w *wm @m@w *wm @m@w *wm @m@ O@=*+z @:/O@=*+z @:/O@=*+z @:/O@=*+z @:/O@=*+z @:/O@=*+z @:/O@=*+z @:/O@=*+z @: :*/- :m: *:*/- :m: *:*/- :m: *:*/- :m: *:*/- :m: *:*/- :m: *:*/- :m: *:*/- :m: )*/O@-Y|- )*/O@-Y)*/O@-Y)*/O@-Y)*/O@zO@)*/O@z zO@)*/O@zO@)*/O O@zO@*/O O@zwO@*/ *):O*zO((@*):O*zO*):O*zO*):O*zO*):O*mO*z):O*mO(O*z):O*(O*z):+:O*(O*):+:O*()O*): m))@z@-+m~m))@z@-m))@z@-m))@z@-m))@z*@z@-m@z*@z@@@-m*@z@@@m@-m*@z@@m@-m*@z @@m@ z:+*O-mm*Yz:+*O-mz:+*O-=O-mz:+*O-=O-mz:+*O--mz:+***-mz:+*)***-mz:+****-mz:-+*** m@: @:~+( m@: @:~m@: @: @:~m@: @: @:~m@: @: @m@: @: @m@/@: @: @m@/@ @: @m@+/@ @ -+(*m- o-)-+(*m- -+(*m-Om- -+(*m-Om- -+(*m-Om-+(*m-Om-+-+(*m-Om-+-+*m-Om-+|-+*m m*m |== *m*m |=m*m |=m*m |=m*m |=m*m |=m*m*m |=m*m*m |=m*m+*m + YY/ + ) + YY/ ++ YY/ ++ YY/*Y/ ++ YY/*Y/ ++ Y*Y/ ++-+ Y*Y/ ++-+ YY/ ++-+* YY/ zY=) w ~/YzY=) w zY=) w zY=) z) w zY=) z) w zY=z) w zmzY=z) w zmzY=) w zmz|Y=) + oY*:+:ow+ oY*:++ oY*:m*:++ oY*:m*:++ oY*:m*:+oY*:m* *:+oY*:m* *:+Y*:m* *z:+Y* @ z++ *zo)@ z++ *@ z++ w+ *@ z++ w+ *@ z++ w+ *z++ w+ + *z++ w+ + *++ w+ +* *++ ()=ww+ *O()=ww+ ()=ww+-w+ ()=ww+-w+ ()=ww+-w+ =ww+-w+w+ =ww+-w+w+ ww+-w+w=+ ww z +wO z +z + +z + +z + + + = + + = + + = ( + o +@~@= ozo +@~@=o +@~@+~@=o +@~@+~@=o +@~@+~@=+@~@+~@~@=+@~@+~@~@=@~@+~@~z@=@~ )(w=++ +~z)(w=++ +~z)(w=++ +~z)(w=++ +~z)(w=++ +~z)(w=++ +~z)(w=++ +~z)(w=++ +~ mz- O @ =mz- O @ =mz- O @ =mz- O @ =mz- O @ =mz- O @ =mz- O @ =mz- O @If you stare at this image by trying to focus on something behind the image, you will be able to see, after some-time, a 3-D scene with the letters F Y I detaching from the background. (If you read this document on a monitor it is easier to focus on your image reflected on the screen in order to get the 3-D illusion. If you read this document on paper, try to put a glass in front of it and do the same thing.) To understand the mechanism which allows you to get this peculiar effect, we should take a look at the process of vision. The feeling of "depth" that you get by looking
at a statue instead of looking at a photo of the same statue, is due
to the fact that the human body has two eyes. In the above example with the statue, we need just one eye to get the general shape of the statue. A humble photo does the same. It is the second eye that provides some "extra" information. This extra information is the "depth" of the various parts of the statue. In fact a "photo" gives just a bi-dimensional (x,y) representation, to get the third dimension (z) you need some "extra".
y
| |---------
| z | Photo |
| / | |
| / ---------|
|/_______ x
By having two pictures of the same object, taken
by two different positions, which is the case of the human eyes, you can
get the "z" coordinate to that object. It is a simple geometrical question.
In fig.1 we assume that there are 2 objects, X and Y which are at the same height (y) and different depths (z) and positions (x)
|------------------------------------------------------------| | Fig.1 | | z | | y | | | Y \ | | | \|_____x | | | | | | | | | | | | X ^ | | | | | | | | | | | (o) (o) | | watching | | left-eye right-eye direction | | (depth) | |------------------------------------------------------------|In fig.2 are shown the kind of "pictures" that each eye gets: (fig.2L -left eye, fig.2R -right eye; the '+' marks the center of each picture)
|------------------------------| |-----------------------------| | Fig.2L | | Fig.2R | | | | | | | | | | | | | | X Y + | | X Y + | | | | | | | | | | | | | | | | | |------------------------------| |-----------------------------|As you can notice the 'X' shifts more than the 'Y' from one picture to another. This is an indication that the X object is 'closer' than Y.
where "dx.hrz.hhh ( A, '+')" means distance (on the horizontal axis) in the hhh picture from object A to origin/center. Furthermore, with good approximation we can say that any objects with the same 'shift' are at the same "depth" (z) In the same way, the eyes forward to the brain two slightly different pictures. It is the brain that must "compute" a 3-D representation of the scene. The difficulty is to know which pairs must be associated to "compute" the z-coordinate. In the example above it's easy to assume that the 'X' from each picture is associated to one 'X' object. The same goes for the two 'Y'. But the images that the brain gets to compute, can be quite complicated. What if there are more X-s and Y-s in each picture ? How does the brain establish the "couples" for which to calculate the shift/depth ? A clue is that each pair must be on the same height (y). Which means that the brain should not try to associate spots, patterns that are located at different heights. But that is not enough ! The 'brain' can make mistakes in this process of designation of pairs! It is that which make possible the 3-D feeling that we get from stereograms. The simplest stereogram that we can get is something like-this: _______________________________________________________________ | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | | * * * * * * | |-------------------------------------------------------------| Column:1 2 3 4 5 6Using the same procedure as in the beginning of this document you should be able to see the same '*' columns but "somewhere behind" this document. In fig.3 (Left/Right) I have represented the kind of pictures that the eyes forward to the brain when looking at the preceding stereogram. (notice '+', the center)
|-------------------------------| |-----------------------------|
| : : : : :Fig.3L | |: : : : : Fig.3R |
| : : : : : : | |: : : : : : |
| : : : : : : | |: : : : : : |
| : : : : : : | |: : : : : : |
| : : +: : : : | |: : : : + : |
| : : : : : : | |: : : : : : |
| : : : : : : | |: : : : : : |
| : : : : : : | |: : : : : : |
| : : : : : : | |: : : : : : |
|-------------------------------| |-----------------------------|
column:
1L 2L 3L 4L 5L 6L 1R 2R 3R 4R 5R 6R
Normally the brain will associate the columns in
the following way:
but it can happen that the brain does the following
association:
Remember: All columns look alike ! Of course it is possible that the brain makes
other associations of these kinds:
It can be noticed that by choosing a diferent association of columns the "shift" between the images of the objects changes. As a result the "depth" of the perceived objects changes. In the association 1L-2R, 2L-3R,... the shift is reduced -> the "depth" increases -> the columns seem somewhere behind. Is it possible to determine exactly the power of the brain in matching complicated images ? I thought, some time ago, what would happen if we put someone in front of a large panel situated at a convenient distance (so that the eyes are relaxed) and the panel is full of randomly disposed spots. The spots should be all alike and in very great number, very small but big enough to not became a uniform gray. The brain should be overwhelmed by the great number of matches that it must try. What will happen ? The person will get dizzy ? get a headache ? Or will the person be forced to see just a gray fog ? Subject: [2] Terminology
Subject: [3] How do I see them?Most Stereogram pictures are usually generated so that if you look at (converge your eyes on) a position twice as far away as the picture, and focus on the picture, generally after a few minutes you see a surprising 3D image! Most people find this extremely difficult for the first time. You have to focus on a point which is different from where you are looking. This is known as "de-coupling" your vision process. Instinctively people focus at the same point they are looking at, and this is the main obstacle in seeing images of this type. This is why most posters come with a reflective surface such as glass or plastic covering them---if you try to look at your reflection you will be looking at a point twice as far away as the actual poster. It has been noted by almost everyone that while this sometimes helps beginners see the 3D effect for the first (and perhaps even the first few) times, experienced viewers to not need any help like this, and indeed the reflection is usually very distracting and decreases the quality of the 3D effect. There are many ways to teach this de-coupling to either yourself or to others, including (in almost no particular order): NOTE: It is generally easier to see Stereograms under bright light. I have been told this is because you eye relies less on focus under harsh conditions. Another point, to see stereo images, you need to have "passable" use of both eyes. If you wear glasses try with and without them on. Some short-sighted people can see them easier without their glasses on (if they get closer to the picture). The pull-back Hold the picture (or move your face) so your nose is touching the picture. Most people than can not possibly focus with something this close to their eyes, and they will be content with their inability to focus. With the picture up close, pretend that you are looking straight ahead, right through it. Now slowly pull the picture (or your face) away while keeping your eyes pointed straight ahead. If you do this slow enough, an image usually appears when the picture is at the correct distance. The reflection As mentioned above, with a reflective surface it is sometimes a lot easier to converge your eyes in the correct position. You simply focus on your nose or some central reflection in the picture, and wait until you focus on the image. The drunk-eyes This method is used to describe the feeling of the process of deconverging your eyes. It is very much like being drunk or having "staring-eyes". Your eyes don't look at the object, but rather through it. This state is common to some in the morning before the coffee caffine fix. The wall, or the finger Hold the picture so that it is half between you and a wall. Look *over* the top of the picture towards the wall, and focus on something such as a picture hook or mark. While keeping this "gaze" either slowly lift the picture or lower your eyes while keeping them converged on the wall. A similar approach (but for cross-eyed viewing) is to stand arm's length away from the picture and put your finger on the picture. While slowly pulling your finger towards your face, keep looking at your finger, you will notice the picture becoming blurry, and at an intermediate position you will (eventually) see the 3D image. The see-through Photocopy the picture onto a transparency. Then focus through the transparency onto something twice as far away. This is similar to (The wall, or the finger) above except now you don't need to change the position of your gaze. Wide-Eyes This method involves building a device to widen your interocular distance, as well as allowing the adjustment of the convergence of your eyes. It's so simple, you almost don't have to be there!. I have had a look through such a device, and the results were very good. (diagram pending...) Cheating... To cheat, photocopy the image onto two transparencies, then overlay them and carefully shift them horizontally so they are about an inch or two out of alignment. Somewhere around this position you will see a rendition of the image. Obviously in 2D not 3D, but you will at last finally believe there is "somethere in there." And if you're still having difficulty, this
comment by jhakkine@cc.Helsinki.FI (Jukka Hakkine), may apply to you: But don't dispair, don't give up until you're tried for at least a month!
Subject: [4] Where can I buy the posters from?For those who do not have a local SIRDS distributor (i.e., the poster cart at the mall), here are a few companies you may be able to order from.
------------- Infix Technologies ------------- $20 Earth (mercator projection of the Earth's
altitudes) These prints are 18x24 inches. Retail price for the 18x24 inch prints is $20 plus $3 s/h. Utah residents add 6.25% sales tax. Wholesale and distributor discounts are available. Quotes for custom work are also available. Cost and minimum order varies, based on content. PO Box 381
------------- Inner Dynamics, Inc. ------------- (Distributors) Glow in the Dark Poster Series - $22 (size: 18" X 24")
Retail prices (USA) stated above plus $3 S&H (USA) - call for overseas S&H. Ohio residents add 5.5% sales tax.
------------- Altered States ------------- 92 Turnmill St,
------------- N.E. Thing Enterprises ------------- Send a catolog request to: Subject: [5] How can I generate them myself?There are many fine programs for generating SIRDS out there in the Internet. The following programs are available from ftp://ftp.cdrom.com/pub/stereograms/stereograms Here is a list of the ones I currently know about:
Subject: [6] Which books/papers should I read?
BooksIn an attempt to make the autostereogram illusion understandable to everyone, I was the lead author of a book titled, "Hidden Images: Making Random Dot Stereograms", published by Que (ISBN 1-56529-994-9). The book takes a practical, application-oriented approach to understanding the illusion. To date, "Hidden Images" is available in English and Spanish versions. We've included a piece of software with the book called POPOUT-LITE, allowing the reader to easily create his own images using only Windows Paintbrush to create depth images. POPOUT-LITE has received many excellent magazine reviews in Europe, and has won an award for outstanding shareware. Bob Hankinson "Stereogram" "Principles of Cyclopean Perception" "Magic Eye: A New Way of Looking at the World"
"Magic Eye II: Three Dimension Trip Vision" "Das magische Auge" (German version of "Magic
Eye")
"Stereo Computer Graphics and Other True 3D
Technologies" "Random Dot Stereograms" "Human Stereopsis. A psychological Analysis"
PapersB. Julesz and J.E. Miller, (1962) "Automatic stereoscopic presentation of functions of two variables" Bell System Technical Journal, 41: 663-676; March.R.I. Land and I.E. Sutherland, (1969) "Realtime, color, stereo, computer displays" Applied Optics, 8(3): 721-723; March D. Marr and T. Poggio, (1976) "Cooperative computation of stereo displarity" Science, 194: 283-287; October 15 D. Marr and T. Poggio, (1979) "A computational theory of human stereo vision" Proceedings Royal Society of London, B204: 304-328 Science, 194: 283-287; October 15 G.S. Slinker and R.P. Burton, (1992) Journal of Imaging Science and Technology, 36(3): 260-267; May/June D. G. Stork and C. Rocca, (1989) "Software for generating auto-random-dot stereograms", Behavior Research Methods, Instruments, and Computers 21(5): 525-534. H.W. Thimbleby and C. Neesham, (1993) "How to play tricks with dots" New Scientist, 140(1894): 26-29; October 9 H.W. Thimbleby, S.J. Inglis, and I.H. Witten, (1994) ftp://ftp.cs.waikato.ac.nz/pub/SIRDS in press. C.W. Tyler and M.B. Clarke, (1990) "The Autostereogram" SPIE Stereoscopic Displays and Applications 1258: 182-196 C. Wheatstone, (1838) "Contributions to the physiology of vision. Park I. On some remarkable, and hitherto unobserved, phenomena of binocular vision" Royal Society of London Philosophical Transactions 128: 371-394 C. Wheatstone, (1838) "Contributions to the physiology of vision. Park II. On some remarkable, and hitherto unobserved, phenomena of binocular vision (continued)" The London, Edinburgh, and Dublin Philisophical Magazine and Journal of Science, series 4, 3: 504-523
Subject: [7] SIRTS/Ascii StereogramsFor people without graphics displays, or simply like having a 3D .signature, you can create a stereo effect using repetitive characters. Text Stereograms (not random) -- the following by Dave Thomas (dthomas@bbx.basis.com)
O O
n n n n n n n n n n n n n n n n
f f f f f f f f f f f f f
e e e e e e e e e e e e e e e e
a a a a a a a a a a a a a
a a a a a a a a a a a a a a a a
r r r r r r r r r r r r r
r r r r r r r r r r r r r r r r
g g g g g g g g g g g g g g g g g g g g
r r r r r r r r r r r r r r r
e e e e e e e e e e e e
a a a a a a a a a a
t t t t t t t t t
>>><<<<>>>><<<<>>>><<<<>>>><<<<>>>><<<<>>>><<<<>>>><<<<>>>><<
d d d d d d d d d
e e e e e e e e e e
p p p p p p p p p p p p
t t t t t t t t t t t t t t t
h h h h h h h h h h h h h h h h h h h h
-- the next few are by DR J (me90drj@brunel.ac.uk)Look for his new upcoming Text Stereogram Guide---out soon!
/^\ /^\ /^\ /^\ /^\
####################################################################
####################################################################
_/ #### _/ ####\ _/ #### \ _/ #### \ _/#### \
/ ## \__/ ## \__/ ## \__/ ## \__/ ## \
____ ## ____ ## ____ ## ____ ## ____ ## ____
/ \## / \ ## / \ ## / \ ## / \ ##/ \
| 2D |# | 2D |## | 2D | ## | 2D | ##| 2D | #| 2D |
| or |# | or |## | or | ## | or | ##| or | #| or |
| 3D |# | 3D |## | 3D | ## | 3D | ##| 3D | #| 3D |
| ?? |# | ?? |## | ?? | ## | ?? | ##| ?? | #| ?? |
| | | | | | | | | | | |
-------- -------- -------- -------- -------- --------
\\\\\\\\ \\\\\\\\ \\\\\\\\ \\\\\\\\ \\\\\\\\ \\\\\\\\
\\\\\\\\ \\\\\\\\ \\\\\\\\ \\\\\\\\ \\\\\\\\ \\\\\\\\
\\\\\\ \\\\\\ \\\\\\ \\\\\\ \\\\\\ \\\\\\
/^\ /^\ /^\ /^\
_ / \ _ / \ _ / \ _ / \ _
/ \_ \_ / \_/ \_ / \_ / \_ / \_ / \_ / \_
/ \ \ / \ \ / \ \ / \ / \
__/ \ __/ \ __/ \ __/ \ __/ \
xx \ /xx \ xx \ \ xx / \ xx / \ xx
x XX x \_ x XX \ x x XX \ x x XX \ x x XX _/ \ x XX
X XX-x-x-XxX--X XX-x--x-XxX-X XX-x---x-XxXX XX-x----x-XxX XX-x-----x- X XX
XxXX X XxX XxXX X XxX XxXX X XxX XxXX X XxX XxXX X Xx XxXX
XXxX __X XXxX __X XXxX __X XXxX __X XXxX __ XX
XX XX XX XX XX XX
__XX ______XX ______XX ______XX ______XX ______XX
(Cactii modified from a drawing by Chris Pirillo)
\ . \ . \ . \ . \ .\ \.
\ . \. . \ . . \ . .\ . \. . \ . .
\\ . \\ . \\ . \\ .\\ \\ \\
\\ . \\ . \\ .\\ \\ \\ \\.
\\. \\ . \\ . \\ . \\ . \\ . \\
* . * . * . * . * . * . *
. . . . . .
. . . . .
. . . . . . . . . . .
. . . . . .
. . . . . . . . . . . . .
___/~\_/\____/~\_/\____/~\_/\____/~\_/\____/~\_/\____/~\_/\____/~\_/\_
_/~~\_ _/~~\_ _/~~\_ _/~~\_ _/~~\_ _/~~\_ _/~~\_ _/~~\_
. . . .
. . . .
+ + + + +
. . . .
* * * *
. . . .
. . . .
+ + + +
* * * *
. . . .
. . . .
. . . .
+ + + + +
. . . .
. . . .
* * * *
. . . . .
. . . .
+ + + + +
. . . .
* * * *
. . . .
* * * *
. . . .
. . . .
+ + + +
. ' . '
. ' * . ' * .
. . .
. ' . '
_' ____________________ ' ____________________ ' _
|____|~~ _ |____|~~ _ |____|
_ _
' = ' =
/ /
. -- ,.. / . -- ,.. /
,` '; ,` ';
.,.__ _,' /'; . .,.__ _,' /'; .
.:',' ~~~~ '. '~ .:',' ~~~~ '. '~
:' ( ) . ; ):;. :' ( ) . ; )::;.
'. '. .=----=..-~ .;' '. '. .=----=..-~ .;'
' ;' :: ':. '" ' ;' :: ':. '"
~~~~~~ (: ': ~ ;) ~~~~~~~ (: ': ~ ;) ~~~~~~~~~
'~ \\ '" ./ '~ \\ '" ./ '~
~ '" '" ~ '" '" ~
Subject: [8] Where is most of the discussion about SIRDS?Most of the discussion about SIRDS has taken place in alt.3d . A lot of people would like to see the death of SIRDS, both due to the overwelming number of people asking FAQ's, and simply because there is much *much* better 3D out there than this! Usually people post requests for information to newsgroups such as comp.graphics...unfortunately these people sometimes get flamed, get told it is *impossible* to draw them...if this has happened to you read alt.3d , viva la difference.
Subject: [9] Internet locations for material
Subject: [10] Stereogram History-- Robert Raymond, Mirages -- Moab, UtahUpdated: 28-June-1994 with comments from Jukka Hakkinen (jhakkine@cc.helsinki.fi) Updated:15-Mar-1996 (Stuart Inglis)
-- A few historical comments by jhakkine@cc.helsinki.fi Julesz also mentions that there had been some prior attempts to make RDSs (Aschenbrenner, C.M. (1954) Problems in getting information into and out of air photographs. Photogramm.Engng. 20, 398-401) but without a noticeable succes because the pictures had been hand cut. Because the methods had been so crude there was a good possibility that these pre-RDSs contained monocular depth cues. Julesz created his stereograms with a computer so they were very precise and the possibility of monocular cues was nonexistent. Naturally the leading researchers at the time (Ogle & Wakefield (1967) Vision Research vol.7, 89-98) did not believe that it was possible and the notion of depth perception without monocular cues remained controversial for a long time. Ogle & Wakefield (1967):
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