Ways to see 3D
In the chapter How 3D Works we learnt that 3D vision and the perception of depth is one of the consequences of having two eyes and brain’s wonderful capacity to create 3D image from two slightly different images of the same object.
So how is that 3D reality we live in recreated in 3D movies and games?
Every 3D technology relies on the stereopsis – ability of brain to create a 3D image upon left and right image from the eyes. So every 3D technology is trying to make each eye see the image it is supposed to see at the same time (or nearly the same time) as the other eye sees its image.
The most effective 3D method before digital age was anaglyph method. Usually two projectors were needed: each projected an image with either red or blue filter (or red / green combination). The paper glasses with red and blue foil for each eye then blocked out the images for each eye, so the 3D effect was created.
The method had many drawbacks: two projectors were needed, the synchronization of them was a big problem and the color of the movies was problematic to say the least. Anaglyph methdo and is considered a history – at least for cinema and consumer electronic world.
Digital projectors are usually capable of projecting the stereo images in a frame-rate that is high enough to recreate the 3D effect with single projector setting. It turns out, however, that most of the passive systems do require dual projector setting due to tremendous loss of light.
The term passive systems nowadays usually applies to systems that use different polarization to separate the stereo images. At the projector either electro-optical modulator or rotating filter wheel is used – filters have different polarization characteristics. To make sure each image makes it into the right eye, viewer wears glasses where each glasses lens has different polarization: one eye has left circular polarization, the other right circular polarization.
There are many disadvantages to passive system: polarization of the light can only be preserved with the silver screen (in case of cinema exhibitors this means a big investment and inability to move a 3D system to other hall in a multiplex), passive systems have significant problems with ghosting (“objects” in a movie having a ghosty shadow) and usualy they require dual projector system to prevent the loss of light.
Read more about the active shutter 3D technology in the chapter XPAND 3D.
