These techniques are similar to the stereo viewing techniques in that no glasses are
required but you have to train your eyes to view them. Some sort of special processing
of the image is required to create one.
In 1844 Sir David Brewster discovered that in repeating patterns with small differences
a three-dimensional effect can be seen. But it wasn't until 1979 that the first Stereogram was
produced by Christoph Taylor on an Apple II. Stereograms were commercialized in the USA in
1990 and fast became a craze, which has all but died out.
Stereograms come in two flavors,
the pattern stereogram - which looks like wallpaper, and the random dot stereogram - which
doesn't look like anything. Stereograms are just pictures with their content scattered in such a
way that they look 3D when one eye looks through one particular part of the image and the other eye looks
through another part. The algorithm for generating a stereogram is long and complex and I wont
bother describing it here.
Above is an example pattern stereogram from Magiceye Inc.
Like most stereograms, this is viewed with the parallel viewing
method (you look through the image). Pick out two objects in the picture that are standing next
to each other. Now make your eyes focus through the screen so that your two objects merge into one.
If one object is above the other tilt your head slightly left or right. Once the
objects are perfectly aligned then with any luck your eyes will focus correctly on the 3D image.
Don't be suprised if you can't see it. I have great difficulty getting it myself. If you can align the objects but
it still looks blurry then this is because your eyes are pointing in the right angles, but the pupils of your eyes are not
focusing correctly. This is your conscious mind getting in the way, try
and convince yourself that the blurry image is actually farther away from you than the screen, imagine focusing
on something far away, and hopefully your eyes will bring the blurry 3D image into sharp focus.
The repeating pattern of these stereograms gives you the clue as to how they work. Really the pattern
need only repeat once, aslong as you have two images you can look though them and see a single
3D image in the distance.
Hidden Image Stereogram
Here is another example, this time the dots that make up the stereo image appear random when
viewed normally. But if you focus through the picture the dots will not appear random, they will
make up a stereo image. These images are generated on computer using a depth map to determine how
to scatter the dots, only computing power makes these sort of Stereograms practical to produce.
Did you see it? no? don't worry, I can't see those things either. I still remember
a British comedian called Jasper Carrot talking about Stereograms, and how he couldn't see the them
and how left out it made him feel around his friends...
Friend: Can you see it?
Friend: Come, you must be able to see it..
Friend: Come on, are you stupid or something? its the statue of liberty, can't you see it?
Carrot: Errr.. umm.. yeah.. err yes I can see it.
Friend: You can ?
Carrot: Errr, yeah yeah, its the statue of liberty.
Friend: Can you see the taxi?
Carrot: Err, yeah yeah.
Friend: There isn't one! hahahahah
The text on the Magiceye books claim that 85-90% of people can see them, hmmm.
Magic Carpet is the only PC game I know of that has a real-time stereogram option. And I don't
know of anyone who actually got used to playing it that way. The problem with stereograms is
that they are simply too much of a hassle to learn to view.