Chapter I

Stereo 3D on computers

Creating a stereo image means first creating two flat images, i.e., a stereo pair: one image for the left eye and one for the right eye.
This is easy to achieve: you render one image with the observer in the left eye position, apply an horizontal offset to the observer position and then render the right eye image.
The offset is called the BASE in the stereoscopy vocabulary and is assumed to be the same as the inter-ocular distance (About 6.5 cm).
The base has to be increased or decreased relatively to the scale of the scene to have a significant stereo effect.
Obviously, you cannot use the inter-ocular distance to view in stereo a chemical molecule or a galaxy.
A typical average value for the base is 1/30 of the distance from the observer to the nearest object of a scene.

Why 1/30? If you stand in front of a window, which opens to a landscape to the horizon, you will notice that you cannot see clearly both the horizon AND the window itself if you stand within two meters away from the window.
When you are two or more meters away from the window, you can view all the scene comfortably from the nearest point (The window) to the infinity (The horizon).
This value of two meters depends on the person but is a statistical value.
The fact is that 6.5 cm (Inter-ocular distance) is about 1/30 of two meters.
So, if you take for the base the 1/30 of the distance from the observer to the nearest object of the scene, you're sure that you will see the full stereo image comfortably from the first point until the last.
You will also be able to see it with enough stereo sensation.
When the base is larger than the average inter-ocular distance, the resulting stereo is called hyper-stereo.
It gives you the sensation of looking at reduced models, as if you were a giant.
On the other hand, when the base is smaller than the average inter-ocular distance, the resulting stereo is called hypo-stereo.
It gives you the sensation of looking at enlarged models, as if you were a Lilliputian.

An error that needs to be avoided is making a stereo pair with converging viewing axes.
It appears natural to use convergence since eyes converge while they are looking at something, although it is not the right way.
When your eyes converge, the point at which they converge appears perfectly clear.
The fact is that everything else appears blurry but you don't notice it because you are used to it.
However, due to the accomodation reflex, when you look at something blurry your eyes will naturely adjust to it.
In a stereo image, all the image has to be clear to be viewed clearly at whatever point you look in the image. Converging on one point would make the image comfortable for all points before the converging point. However, this would be difficult for points after it to fuse.
By converging at the infinity, i.e., keeping viewing axes parallel, all the image will be easy to fuse.

Things become a little more complex when you want to see in stereo a stereo pair . . .
To fuse the two images you've produced in a stereo one, each eye must see only its own image.
Different solutions have been found over the years, mainly a result of the use of stereo pairs from stereo cameras used during the 50's and 60's.
You can use a lens stereoscope but you will have to transform your two images onto slides.
You can also use a mirror stereoscope (If you can find one . . .) but you will have to print your images.
It's possible to directly use the screen but that will divide the usuable surface on the screen into two; as you will have to display the two images side by side.
If you do not have stereoscope, you could train to "free-view" by crossing your eyes with the right view on the left and the left view on the right as many stereo enthusiasts do.
You will need time and patience as it is not totally obvious.

You can have a try with the stereo pair below : viewed in stereoscopy you'll notice that there is one ring not connected to any of its neighbours.

The best known solution is to write your own "SoftStereo" code.
Then, use LCD shutter glasses.

The trouble is that this solution is not adapted for your aim if you just want to make some stereo images yourself.
You can do this out of curiosity to see what it looks like by using your own computer and software you are accustomed to.

To do so in a cheap and quick way is absolutely possible, but, (Of course there is a but) there will be some restrictions about the kind of images you will be able to convert properly into stereo.
However, that will give you the opportunity to verify by yourself the interest to escape "flatland".