Stereoscopic display techniques



At Eyes, JAPAN three-dimensional videos are shot with 2 identical cameras mounted on a frame to ensure their adjustment which simply record two movies: One for the left eye and one for the right eye.


Two important terms are stereo base and sweet spot. Stereo base is, simply put, the space between the lenses of the cameras, like the eye distance. We usually use 7.7 cm. The sweet spot is the distance to the camera lens where the 3D effect is most apparent. The sweet spot depends on the stereo base as well as on the type of camera lens used. Therefore it requires a bit of testing to find the sweet spot for a new set-up.


Display techniques using glasses:

Active stereo: This is actually a quite old method to display 3D images which originates in the 1980's. It's the most popular though, since it can play high resolution movies. The display screen quickly alternates between the left eye view and the right eye view displaying the movies. Therefore special "active shutter" glasses are needed to view the three-dimensional movie. The display has a maximum refresh rate of 120 Hz, therefore being able to display a smooth 60 Hz frame rate for each eye. A minor drawback is, that the necessary glasses are rather expensive (~US$ 500)

Passive stereo: In front of the display a polarization filter is placed which rotates the polarization layers for the left eye to 90° to the left (even line numbers) and for the right eye to 90° to the right (uneven line numbers). Because all lines in the movie with even numbers are for the left eye and all uneven for the right eye this is an interlaced method. In contrary to the aforementioned method, passive stereo uses much cheaper glasses (~US$ 2). The drawback is that the vertical resolution is only half the original resolution due to the interlacing.


Display techniques without glasses:

Parallax Barrier: This is also some kind of "filter" which has to be placed in front of the display to allow the viewer to get a three-dimensional impression of the movie. Basically, it is a barrier with different slits in it so the viewer's left eye and right eye only see the pixels of the component movie thats supposed to be viewed by that eye. The big advantage of this is that no additional glasses are needed and it works even with displays up to 200", but the viewer has to sit in a well-defined spot in front of the display for the parallax barrier to work correctly.

Lenticular: In this method the display is a huge array of small lenses which route the light from each pixel a special way so it meets the eye for which that particular pixel was meant for. This makes the technology much more expensive than Parallax Barrier. Another drawback is the display size, which is very limited and no match to Parallax Barrier.