Retrofitting TVs for 3D

Reader Sam emailed me with a very interesting question:

Your review of a 3D TV on Monday was very interesting. I have an LCD HD TV which handles 1080p 50Hz inputs,  as would most, if not all, HD TVs. It would be a simple matter to synchronise polarising glasses to alternate frames with a simple set top box, which should be a lot cheaper than a full HD compatible unit. Why can’t 3D TV be presented in such a manner?

Actually, I was reporting on the Panasonic 3DTV launch, rather than doing a formal review. But back to the question.

The problem is that in order to synchronise the shutters in the glasses to the display of frames on the TV, information from inside the TV is required. The device suggested would only know about the signal being fed into the TV.

The various TV technologies are quite variable in how long they take to organise and process the signals prior to displaying them. Some manage it in a few tens of milliseconds. High end Philips TVs take about 200 milliseconds, or one fifth of a second. There’s no way an external device could know this.

Both Sony and Panasonic at their respective launches made bit of a thing about how their technology reduced ‘cross talk’ between the eyes by switching more cleanly and precisely than competing technologies. Whose is better I don’t know. What I do know is that it is clearly an issue if they both felt compelled to talk about it. Given that with a 50 hertz system each eye is receiving its picture for just 20 milliseconds, even a drift of a millisecond or two would probably be fatal to the effect.

I suppose one could have some kind of delay knob on the device, but that’s a level of complexity I’m sure everyone is keen to avoid.

Oh, one more thing: there are differences between the plasma and LCD versions of the 3D shutter glasses, due to the fact that LCD displays are polarised while plasma ones aren’t.