Most 3D in the home works in a very different way to cinema 3D installations. So far, most 3D TVs use a system requiring ‘active’ glasses. These use liquid crystals to alternately flash their left and right lenses transparent and opaque. This is kept in sequence with flashing pictures on the TV screen, so that each eye sees only the particular frames that it is supposed to.
But most cinemas use the RealD 3D, system. The glasses aren’t active, but passive. That is, nothing in them changes. Instead, all the action happens in front of the projector lens. An active polarising overlay sits in front of the lens and applies polarisation to the picture, switching between so-called clockwise and counter-clockwise polarisation in time with the projector flashing up left and right eye frames. The same sort of effect can be achieved with two projectors with permanent polarising filters, but that’s quite a bit more expensive.
We won’t get into this polarisation stuff too far here. All you need to know is that light waves have a characteristic twist. But some twist clockwise, some the other way. Special filters can be used to allow only one or the other to go through. An active filter on the front of a projector lets the clockwise twisting light of the right-eye view through for an instant. The right lens of the passive eyewear only admits clockwise-twisting lights, so that’s the only picture that eye sees.
So the difference between the home and the theatre is that the cinema uses cheap glasses, and an expensive active polarisation rig in front of the projector. Makes sense, since the glasses are cheap enough to sell to cinemagoers. In the home, the left and right eye images are flashed in sequence and active glasses are used to separate them.
LG has new 3D TVs out using a polarisation filter on the TV and passive polarised glasses, but this is not the same as the cinema system. Passive polarisation is used on front of the TV, with half the pixels of the TV polarised for clockwise-twist, and the other half for anticlockwise. This seems to work quite well, but comes at a cost: each eye sees only half the resolution because every second pixel is opaque to it.
Now Samsung has announced a deal with RealD which should yield TVs that work like the cinema system. Whenever you’re watching 3D material an active polarising filter over the front of the TV screen would come into operation. You’d need only the same passive – and inexpensive – RealD 3D glasses that you use in the cinema, but get the full resolution of the TV screen.
This sounds promising, but we’ll have to wait and see if this system proves more economical than the current shutter-eyewear systems.