Hyperstereo

"Hyperstereo" refers to a stereo image which uses a larger than normal stereo base (the distance between the left and right lenses). Recall that "normal" image separation is about 65 mm, so anything further apart than this is, by definition, hyperstereo.

Usually this is obtained by using two camera separated by a greater than normal distance, or by using a single camera, making two images separated by more than the normal distance. Depending on the subject, this distance can be tens or even hundreds of meters apart. This gives a stereo effect to objects like mountains which are far enough away that normally you would perceive no depth.

STEREOPSIS

To understand why this is not possible we need to consult some theory. The ability of extracting depth information from our binocular vision is called Stereopsis. One of its conditions is related to the fact that our eyes have a certain distance to each other.

Now, if we look at an object in this image the blue dot both our eyes will immediately turn towards the object, leading to a vision of the object in both retinas, resulting in one single vision for both eyes.

The lines represents the distance between us and the object. The horizontal blue line is relative to what is called baseline in the context of stereoscopy, i.e. the distance between our eyes, or the distance between the two camera lenses. Of course our eyes are round not half spheres as shown here for simplicity, but the closer the object the greater the difference between the position of the blue dot in the two images

One could assume that every object which is as far away from us as this would cause a single vision. But this is not true. The object has two positions one for each eye.

Those different positions on the retinas cause a double vision which enables our brain to sense the distances of objects. We also use additional techniques such as comparison of size, movement, etc. to enhance that sense, but we can ignore that for this discussion of stereopsis.

Note that this is only the theoretical horopter. There also exists an empirical horopter and a certain neuronal tolerance, summarised in the so called Panum’s fusional area. But we will just focus on stereopsis.

Unfortunately, the double vision method works only for close objects relative to the base distance of our eyes.

If the relative distance of the dot from our eyes (Y) to the base distance (X) becomes greater the former double vision of the blue dot transforms into a single vision. This means stereopsis is not possible anymore and we are thus not able to sense the different distances of the object as it is seen in two eyes — we are just too far away now.

If a stereo picture is taken of a large, distant object Y such as a mountain or a large building using a normal base X it will appear to be flat. This is in keeping with normal human vision - it would look flat if one were actually there although our brains will make it 3D; but if the object looks flat, there doesn't seem to be any point in taking a stereo picture, as it will simply seem to be behind a stereo window, with no depth in the scene itself, much like looking at a flat photograph from a distance.

This problem affects stereoscopic photography more than in real vision. If you want to take a photo of something that is just too large to fit entirely on your lens — like a building, a mountain, a landscape or a city panorama — the only way is to get farther away from the subject Y and thus loose the stereo effect. Furthermore, we sometimes wish to get closer to particular object but we can’t — like a ship on the sea, an animal or the clouds.

We could conclude that it’s just impossible to sense depth in distant clouds. But obviously clouds are also as three dimensional as is a mountain this is because our brains fill in the detail. Luckily, even in photography, we are not only able to bring back the depth, we are also able to make it visible in a way that we have never seen it before by changing the base distance X.

This is called Hyper Stereo!

HISTORICAL HYPER STEREOS

Hyper stereoscopic photography is no new discovery, but was used for the same purpose as today as it was in the 19th century:

Steve Cushing Impresionist Fine Art Photography

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