In privaten Zirkeln und zunehmend auch ungeniert in der Öffentlichkeit greift man immer Öfter zu den Bildern, die etwas MysteriÖses in sich verbergen. Die Bilder zeigen verschiedenste, auf den ersten Blick eher unspektakuläre;, Tapetenmuster, die sich - bei "richtigem" Schielen - wie von Zauberhand in 3D-Bilder verwandeln. Mitunter bilden sich vor den plakatgrossen Bildern in Warenhäusern starrende Menschenklumpen. Ab und zu ertÖnt dann der Aufschrei: "lch seh's!", kommentiert von den Stereogramm-Profis mit einem lässigen "...ist doch leicht" und von den Ungläubigen;, die immer noch nichts sehen mit "...so ein BlÖdsinn;". Die Wahrheit: über 90 Prozent der Betrachter sind, wenn auch überwiegend erst nach einigem Training, in der Lage, die den Stereogrammen innewohnende dreidimensionale Wirkung zu erkennen.
Ein Alter Hut!
Der englische Physiker C. Wheatstone untersuchte den Effekt der
Querdisparation, das heisst, die Verschiebung zwischen dem
Bildeindruck des rechten und des linken Auges bei der Betrachtung
eines Gegenstandes, bereits um 1838. Mit Hilfe eines neuen Apparates
namens Stereoskop, das den Augen zwei Teilbilder getrennt
zuführt;, gelang ihm der Nachweis, dass das menschliche Gehirn
die räumlichen Informationen einer Szene unter anderem aus
dieser Querdisparation rekonstruiert. Wheatstones Erkenntnisse fanden
schnell den Weg in Wissenschaft und Technik: Bis heute nutzen
Archäologen;, Bodenkundler, Raumfahrer und Nachrichtendienste
Stereoskope zur räumlichen Visualisierung. Aber nicht nur in der
Forschung fanden Wheatstones Erkenntnisse Anwendung. Um die
Jahrhundertwende ergÖtzte sich so manches Mitglied vornehmer
Herrenclubs mit Hilfe von in edlem Mahagoni und Messing gearbeiteten
Stereoskopen an den räumlichen Reizen entblätterter
SchÖnheiten.;
Stereo - oeretS
Neue Erkenntnisse bei der Untersuchung von Raumwahrnehmung
führten auch zu neuen Techniken der Bildgenerierung. Inzwischen
gibt es eine ganze Reihe von MÖglichkeiten zur Erzeugung von
Stereogrammen, die sich im wesentlichen in der Darstellung und der
Zuführung der Bilder zu den Augen unterscheiden: Anaglyphen-
oder Siebverfahren beruhen auf der unterschiedlichen Einfärbung
oder Polarisation, aber der gleichzeitigen Darstellung der Bilder.
Eine Brille mit unterschiedlichen Gläsern filtert für jedes
Auge den richtigen Anteil der Bildinformation heraus. Bekannte
Beispiele für diese Technik finden sich in Kinofilmen aus den
fünfziger und sechziger Jahren, ("polarisierte Version von "Bei
Anruf Mord", rotgrüner Version von "Das Ungeheuer aus der
Lagune") aber auch in jüngster Zeit am Bildschirm.
Tachistoskopische Darstellungen versetzen die Bilder in der Zeit.
Eine Shutterbrille schliesst das Blickfeld jeweils für eines der
beiden Augen, das andere sieht derweil das korrekte Bild. Einige
VirtualReality-Systeme arbeiten nach diesem Prinzip. Beim klassischen
Spreizverfahren führt eine Optik (Stereoskop) die einzelnen
Bilder den Augen im richtigen Sehwinkel zu.
Das Autostereogramm
Der Effekt der Autostereogramme wurde vor über drei
Jahrzehnten von einem Mitarbeiterder Bell-Laboratories, Bela Julesz,
entdeckt. Der geneigte Betrachter kann nun ohne jede Sehhilfen
auskommen. Autostereogramme fassen die Abbildungen für linkes
und rechtes Auge in einem einzigen Bild zusammen. Obwohl ein
Autostereogramm verwirrend und kompliziert erscheint, sind die Regeln
zur Erzeugung relativ einfach. Zur Veranschaulichung stelle man sich
zwei Punkte P1 und P2 im Raum vor, die vor dem Betrachter in gleicher
HÖhe über dem Horizont liegen, aber sowohl vertikal als
auch in der Tiefe nicht dieselben Koordinaten haben (Abbildung weiter
unten). Beim Betrachten dieser recht einfachen Szene sieht sowohl das
linke als auch das rechte Auge je zwei Punkte, was man durch Zuhalten
des jeweils anderen unmittelbar einsieht. Von Ausnahmesituationen
abgesehen, in denen man besser aufs Autofahren verzichten sollte,
sind nur zwei Punkte zu erblicken. Dies liegt an der Fähigkeit
des Menschen, die beiden unterschiedlichen Bildeindrücke
für linkes und rechtes Auge zu einer dreidimensionalen
Wahrnehmung zu verschmelzen.
Befindet sich nun zwischen Betrachter und den beiden Punkten eine durchsichtige Folie, so kann man auf dieser die Schnittpunkte der Strahlen von beiden Augen zu beiden Punkten markieren. Wenn jetzt P1 und P2 aus der Szene entfernt werden, und nur die Folie mit den vier projizierten Punkten in ihr verbleibt, so sieht der Betrachter nach wie vor das gleiche: Vier vordergründig erscheinende oder zwei räumliche Punkte. Eine solche Folie liefert damit ein Minimal Autostereogramm.
Nun besteht eine Szene im Normalfall aber nicht nur aus zwei Punkten. Dennoch lassen sich komplexere Szenen nach dem gleichen Prinzip erstellen. Für jeden Punkt einer 3D-Vorlage liegt fest, wohin seine Abbildungen auf die Folie fallen. Damit diese Abbildungen tatsächlich berechenbar bleiben, muss man die Szene in endlich viele 2D-Punkte aufrastern. Die Tiefeninformation der ursprünglichen Szene darf dabei aber nicht verlorengehen. Als LÖsung des Problems bieten sich sogenannte Tiefenbilder an, in denen jedem Pixel eines Rasterbildes ein Tiefenwert in Form von Farbe oder Helligkeit zugeordnet ist. Je heller eine Bildstelle des ursprünglichen Tiefenbilds ist, um so näher erscheint dieser im Stereogramm dem Betrachter. Deshalb sind normale Bilder für Stereogramme untauglich, da die Helligkeitsinformation in diesen nichts mit der räumlichen Abstufung der Objekte zu tun hat. Die meisten wirkungsvollen Tiefenbilder werden darum meist in 3D-Computer-Programmen erzeugt.
In order to view 3D stereo images you must have two eyes that work together as a coordinated team. Believe it or not, people with glass eyes have actually asked why they can't see anything in those darn Magic Eye 3D pictures. Sorry, two working eyes are definitely required. Check your equipment before continuing.
Looking in the mirror to make sure you have two eyes is not an adequate inspection of your 3D viewing equipment. If you are having trouble seeing 3D, the first thing you need to do is find out whether you have binocular vision and stereo vision . You've got to have stereo vision to experience depth perception and 3D illusions.
Less than five percent of the population have severe visual disabilities that make stereo vision extremely difficult or impossible. This group includes those who have lost an eye or those with severe amblyopia (lazy eye) or strabismus (eye turns -- "crossed eyes" or "wall eyes").
Consider testing your own binocular vision with The Framing Game . It's worth checking because binocular vision problems are more common than you think. At least 12% of people have some type of problem with their binocular vision.
Keep in mind that many people (even those with amblyopia and strabismus) can learn to use both eyes together with the help of vision therapy
Two Eyes = Two Separate Views!
Human beings generally come equipped with two eyes and one head. Make
sure you have these necessary parts before attempting to see 3D.
Unlike horses, humans have two eyes located side-by-side in the front of their heads. Thanks to the close side-by-side positioning, each eye takes a view of the same area from a slightly different angle. The two eye views have plenty in common, but each eye picks up visual information the other doesn't. Have you ever compared the different views of your right and left eye? The Eye Hop Game lets you do just that.
Two
Eyes = Three Dimensions (3D)!
Each eye captures its own view and the two separate images are sent
on to the brain for processing. When the two images arrive
simultaneously in the back of the brain, they are united into one
picture. The mind combines the two images by matching up the
similarities and adding in the small differences. The small
differences between the two images add up to a big difference in the
final picture! The combined image is more than the sum of its parts.
It is a three-dimensional stereo picture.
The word "stereo" comes from the Greek word "stereos" which means firm or solid. With stereo vision you see an object as solid in three spatial dimensions--width, height and depth--or x, y and z. It is the added perception of the depth dimension that make stereo vision so rich and special.
Stereo Vision Has Many Advantages
Stereo vision--or stereoscopic vision --probably evolved as a means
of survival. With stereo vision, we can see
WHERE objects are in relation to our
own bodies with much greater precision--especially when those objects
are moving toward or away from us in the depth dimension. We can see
a little bit around solid objects without moving our heads and we can
even perceive and measure "empty" space with our eyes and brains.
If You've Got Stereo Vision, Count Your
Blessings!
According to the web site of the American Academy of Opthalmology,
September, 1996: "many occupations are not open to people who have
good vision in one eye only [that means people without stereo
vision]"
Here are a few examples of occupations that depend heavily on stereo vision:
Here are just a few examples of general actions that depend heavily on stereo vision:
Are You Sure You've Got Stereo Vision?
It's hard to know what you're missing, if you've never had it. Do you
see with both your eyes? Are your two eyes similar or different in
sight?
This Is Just A Test -- of Your Stereo Vision
System
Are both your eyes turned on and working together as a team?
Try this easy test and find out if you are a good candidate for 3D
viewing. It's The Framing Game and it only takes a
minute!
THE FRAMING GAMEIn order to see 3D your brain has to use the visual information
from both eyes. If the two eye views are too different and cannot be
matched up, the brain will be forced to make a choice. It will reject
all or part of the information from one eye. The brain can suppress
or turn off visual information it cannot use. The Framing Game can
tell you whether both your eyes are TURNED
ON at the same time. The illustration to the left
demonstrates what should happen.
SUCCESSFUL?
Both your eyes are ON and you are an
excellent candidate for 3D viewing fun. Continue with this guide and
enjoy!
PROBLEMS?
This demonstrates the different angles of view of your two eyes. It's also a chance to check whether your eyes see equally well. Is one image blurrier than the other? Is there a size difference between the images? Does one image seem more comfortable or reliable than the other?
The Logical Approach to Seeing 3D
-- Understand Where to Aim Your Eyes --
Normally,
if you look at or read something on the computer monitor, you aim
your eyes directly at the surface of the monitor. We're assuming
you've already mastered this technique (you've probably had plenty
of practice). If you use normal viewing to look at 3D images at
this site, you just won't see 3D.
With
the parallel method (a.k.a. the Magic Eye method), the lines of
sight of your eyes move outward toward parallel and meet
in the distance at a point well behind and beyond the image.
That's why it's called parallel viewing. When you
parallel-view, the muscles inside your eye that control the
focusing lens relax and lengthen.
Another
method for 3D viewing is called cross-viewing or the cross-eyed
method. You aim your eyes so that the lines of sight of your eyes
cross in front of the image. When you cross-view, the muscles
inside your eye that control the focusing lens contract strongly
and shorten.
The Language of 3D VisionVISION: The act of perceiving
visual information with the eyes, mind, and body.
BINOCULAR: Of or involving both
eyes at once
BINOCULAR VISION: vision as a
result of both eyes working as a team when both eyes work together
smoothly, accurately, equally and simultaneously.
STEREO VISION: (stereopsis or
stereoscopic vision): a byproduct of good binocular vision vision
wherein the separate images from two eyes are successfully
combined into one three-dimensional image in the brain.
BINOCULAR DEPTH PERCEPTION: a
result of successful stereo vision the ability to visually
perceive three dimensional space the ability to visually judge
relative distances between objects a visual skill that aids
accurate movement in three-dimensional space.
BINOCULAR VISION DISABILITY: A
visual defect in which the two eyes fail to work together as a
coordinated team resulting in a partial or total loss of binocular
depth perception and stereoscopic vision. At least 12% of the
population has some type of binocular vision disability. Amblyopia
and strabismus are the most commonly known types of binocular
vision disabilities. AMBLYOPIA ("lazy
eye"): a visual defect that affects approximately
2 or 3 out of every 100 children in the United States. Amblyopia
involves lowered visual acuity (clarity) and/or poor muscle
control in one eye. The result is often a loss of stereo vision
and binocular depth perception. Vision therapy can benefit this
condition, but early detection can be vital. If the weak eye
misses critical development during childhood, its vision cannot be
corrected to 20/20 acuity with lenses. A consultation with an
optometrist or opthalmologist who offers supervised vision therapy
is recommended with this condition.
STRABISMUS ("crossed eye" or "wall
eye"): affects approximately 4 out of every 100
children in the United States. It is a visual defect in which the
two eyes point in different directions. One eye may turn either
in, out, up, or down while the other eye aims straight ahead. Due
to this condition, both eyes do not always aim simultaneously at
the same object. This results in a partial or total loss of stereo
vision and binocular depth perception. The eye turns may be
visible at all times or may come and go. In some cases, the eye
misalignments are not obvious to the untrained observer. A
consultation with an optometrist or opthalmologist who offers
supervised vision therapy is recommended with this condition.
VISION THERAPY: (also known as
vision training): therapy involving exercises which are aimed at
improving visual skills such as, eye teaming, binocular
coordination and depth perception, focusing, acuity (clarity of
sight), and "hand-eye" or "vision-body" coordination. Vision
therapy can involve a variety of procedures to correct
neurophysiological or neurosensory visual dysfunctions. Practiced
by optometrists, ophthalmologists and vision educators.
ORTHOPTIC THERAPY: a restricted
form of vision therapy which teaches only the abilities of eye
teaming and visual acuity and does not treat other visual
dysfunctions that may be addressed in other types of vision
therapy. This therapy first became popular in Europe in the 1900s.
David Wells, M.D., an ophthalmologist at Boston University, is
credited with introducing orthoptics to the U.S. in 1912. Still
practiced by optometrists, ophthalmologists and orthoptic
therapists.
BEHAVIORAL OPTOMETRY: an
international branch of optometry that specializes in the practice
of vision therapy. Behavioral optometrists will sometimes consider
how environmental, nutritional and/or behavioral factors affect
visual health.
OPTOMETRIST: a doctor of
optometry who diagnoses and treats visual health problems as
dictated by state law. In most states, optometrists are licensed
to examine visual health, prescribe glasses and contact lenses,
fit special devices for vision-impaired individuals, treat some
eye diseases, prescribe some drugs and perform vision therapy.
OPHTHALMOLOGIST: A doctor of
medicine (M.D.) specializing in diseases of the eye and
surgery.