Generations of spectaclesSeveral technologies now exist beyond those things that required spew buckets and seasickness tablets. They can be generically categorised as active and passive. Active 3D glasses have some communications or interaction with the display you are viewing, while passive technology simply sits on your head, and that is about it. No wires, cables or communications. Within active and passive type glasses, there are several different ways to create the illusion of 3D.
Active:* LCD Shutter glasses.* Head mounted display glasses.
Passive:* Linearly polarised glasses.* Circularly polarised glasses.* Infitec glasses.* Complementary colour anaglyphs.
Active 3D technology is the most prevalent in home and scientific/visualisation markets, and seemingly will be the choice of the next generation 3D push for consumer dollars. With Nvidia and ATI actively putting investment and research into the technology, one can assume that it's set to become a mainstream sales channel. LCD shutter glasses are used in Nvidia's current Geforce 3D Vision kit, as well as the high-end professional-stereo products used in the Quadro line of GPUs. The technology works on the basis of alternate frame sequencing and time division multiplexing (TDM). The LCD containing glass becomes dark when a current is applied, but when the current is taken away, it's transparent again. A timing signal is sent via IR, BlueTooth or Wireless 802.11x in synchronisation with a frame lock generator from the image being viewed on the display in front of the user. The glass darkens over one eye, then the other, in synchronisation with the frame rate of the display (generally 120Hz or above). The display itself provides a slightly different perspective for each eye, which is alternated one frame for the left eye, one frame for the right - shot or composited with two separate cameras. For this reason, films such as those destined for 3D are composited/rendered in 48 FPS, rather than the standard 24.
Similarly, in other active 3D systems, the head mounted LCD display close to the eyes, uses a combination of the binocular effect and alternate frame sequencing to achieve a 3D representation or sensation. The head mounted LCD however has been often associated with headaches and motion sickness.
Passive systems sound less cool (let's face it, nobody wants to be passive about anything these days. If we were more passive, there might be less war), but they have benefits and abilities that active systems do not.
Linearly polarised glasses act upon two images laid upon each other slightly offset or superimposed through orthogonal polarising filters in a projector. The glasses the viewer is wearing also contain orthogonal polarising filters, and because of this, and the angle at which the light from each image hits the lenses in the glasses the viewer only sees one image per side of the glasses, and as a result, formulates the now familiar binocular effect of depth. The disadvantage here is that because linear polarisation works exclusively upon the angle of light entering an object, tilting the head or moving destroys the illusion.
Issue: 137 | June, 2012