There are two old fashioned techniques for viewing the two photos taken
from a stereo camera. These techniques have been known about since 1833 when
Sir Charles Wheatstone created a stereo viewing machine. These
pictures can be seen with the naked eye and I will show you how.
This technique I find the easiest. Below is a cross-eyed image, its the same Quake
picture that we saw earlier.
To assist you, I have placed a yellow dot in each picture. The idea is to make yourself
go cross-eyed so that the two dots join and form a third dot in between them which is closer to you. Below
is a diagram of what you should make your eyes do.
Go as cross-eyed as you can, then gradually let it out until both dots
meet. Tilt your head slightly left or right until they are perfectly aligned and
then allow your eyes to adjust and relax in the new position. After the two dots are
perfectly aligned try and relax - let your eyes roam around the picture, but only a little, and keep your focus on the center dot.
Your eyes are now looking at the correct place as if the object is closer to you, your pupils are also focused
as if the object is closer to you also. This isn't the case because the images are really on the surface of the screen. You
want your eyes to be pointed as if the object is closer to you, but your pupils to focused on the screen farther away.
The focusing of your individual eyes is mostly a subconscious process. Just keep the middle dot aligned, relax as best you can, and wait a few
minutes. You should see the stereo image in focus within a couple of minutes. If you still can't
see anything, then rest your eyes before trying again as going cross-eyed like this can cause
eye strain and even temporary short-sightedness.
Parallel Viewing Technique
Here is a parallel pair of images. It's the same Quake picture we saw earlier, only the images
are reversed. To see this, the viewer does not go cross eyed. Instead the right eye looks through
the right picture and the left eye looks through the left picture.
To see a single 3D image you must force your eyes to focus on a focal point
beyond the screen. To prevent eye-strain, I recommend that you print this
picture off if you intend to spend any time on this technique. Below is a
diagram of what you need to make your eyes do.
You will probably find this very difficult. For assistance, try putting a piece of paper
between the two pictures and up to your nose. This this will prevent each eye from looking
at the wrong picture. You can also use the
yellow dots as guidelines. You must focus your eyes stereoscopically to get the two dots to split and join in the middle
to form a third dot in the distance. The pupils of your eyes will focus in the distance too but you
don't want this to happen, instead you want the pupils of your eyes to focus on the screen as this is
where the actual picture is.
If you still can't get it, then don't worry, I can't either - and I had my
eyes checked and the optician said they were perfect. This is just a very tricky thing
to do because you are asking your visual system to perceive an object as being both far
away and closer to at the same time.
One limitation of this technique is that the content of the two pictures can't be too far
apart, and therefore the pictures must remain small, if they are two far apart then you
eyes will have to do this.
I saw one guy on TV who could make his eyes to this. I don't recommend practicing
it though :). By the way, viewing machines for these kinds of images contained lenses to magnify the
image so they don't look so tiny.
Stereograms, which I will mention later, are a variation of this.
There are numerous different type of machines that show a stereo pair of images to the viewer.
The most popular kind is probably the "View Master" which most of you have probably seen in
These machines are basically an assisted version of the parallel viewing method. They contain
lenses to magnify the image and make sure that each eye only looks at the image it was meant to see.