Stereoscopic technology

Stereoscopic technology

How is it made

All the technologies of 3D-video use the same principle: the video is recorded from two positions separated by a distance equal to the average distance between the centers of human eyes (60 - 70 mm). As a rule, it's done with two cameras attached to the special rig (Fig. 1) , or with special 3D-camera with two lenses.

Стерео камеры

Fig.1. Tripod for a stereo camera

In case of creating an animated movie, a double rendering of the scene is done - with two cameras corresponding with viewer's eyes.

There is also the technology of creating three-dimensional images by distorting the original video frames to obtain 2x frames corresponding to the left and right cameras.

How we see it
Through a century of development of 3D-cinema we discovered several technologies that allow us to watch videos in 3D.
It should be noted that the stereoscopic technology - the one that allows us to see three-dimensional images on the flat screen - is often called 3D-technology, even though it also involves the entire sphere of computer graphics, which is used to create animated movies and special effects .
Further we will be using the term 3D-video to refer to stereoscopic video.
Currently several stereoscopic technologies are being developed around the world, each of which has its pros and cons. However, each of these technologies use the founding principle of 3D-video - separate images being given to each eye.

Anaglyph technology

Fig.2. The operating principle of anaglyph system

Two superimposed images are being projected to the screen: one in red tones, the other - in cyan. Glasses must also have lenses of the same color. Cyan image can only be seen through the cyan lense, and red - through the red one.
There are other types anaglyph pairs:
red - blue

Technology Pros: low cost, easy to use - no special monitor or projector required.
Cons:  color irregularities often occure,eyes get fatigued fast, requires the use of two projectors.
Anaglyph system (color separation) is actively used in 3D pictures, showcasing short movies at exhibitions, etc. It is hardly used in movie theaters anymore and is replaced by other technologies.

  Infitec (Dolby 3D)

This technology is an evolution anaglyph system.
It is based on the color separation within the range of colors (color waves) (Infitec comes from the words «Interference filter technologies» - technologies associated with the interference effect). Different colors are used for different eyes (as in anaglyph technology), but they are not separated into two colours but into strips within the spectrum of those colors, which allows for much better stereo quality.
This technology requires the use of special glasses with filters, which are hard to produce due to the whole range of colors used.These glasses have a relatively high cost, and that is one of the main disadvantages of the technology.
However, in comparison with the polarization technology (which will be discussed below), this method allows you to save on the cost of the screen (it doesn't require silvered or aluminized screen) which is why the technology is widely spread in 3D-cinemas.

Polarization technology

It is based on the polarizating separation of light waves. Polarized light waves oscillate in perpendicular to their proliferation and appropriate filters are able to transmit light with a specific angle of inclination of the plane of polarization. For example, the linear polarization filter for the left eye is polarized at a 45 ° angle, and the right - at 135 ° angle. They are polarized perpendicular to each other, which means that one misses half of light waves. This way, each lense will let through only the image directed for one eye.
Technology Pros: High quality 3D-effect, the use of one projection system for a large number of viewers, the most convenient solution for long 3D-movies.
Cons: slight imperfections in the separation of images due to the scattering properties of the screen, 3D-stereoscopic technology equipment requires space to install, the complexity of the installation of the equipment, a special 3D- screen.
Application: 3D-Cinema, big 3D shows, exhibitions and activities for science and education, for complex projects .

Polarization technology is used in IMAX 3D and RealD theaters.

IMAX 3D technology uses linear polarization. RealD 3D technology uses circular polarization of light. This technology is similar to the IMAX with the difference that the circular polarization allows to avoid ghosting during small lateral head tilts.

Active shutter technology

This technology uses an alternate displaying of the images, made for each eye and synchronised shuttering of the eyeglass lens, so that each eye sees a frame meant for it. Due to the inertia of the human eye, an illusion of a solid three-dimensional image is created.

Active shutter pros: high image quality, easy to install and configure, is supported by many manufacturers, availability, the best solution domestic use, the ability to integrate complex 3D-systems.
Cons: special requirements for 3D-equipment (high frequency of 3D-display/3D-projector - 120 Hz), expensive 3D-glasses, is inconvenient for mass events.

Lenticular lense technology

Does not require special glasses, but is also based on the principle of stereoscopy for monitors and TVs. Images for each eye are separated with a special film applied to the monitor screen, that possesses certain optical properties. Microlenses refract the image at different angles so that a person in a particular viewing area receives different images for the left and right eyes.
The technology is still in its infancy, because the generated 3D-effect is obtained only when the person is in a particular viewing area. Nevertheless, experts predict the technology could be used in such crowded places as railway stations, supermarkets, exhibitions, etc.