Another use for 3D TVs

It seems that just about every manufacturer is planning to launch 3D-capable TVs this year. Most of them use high frequency refresh rates, synchronised with LCD shutter specs, to present a different image to each eye: the screen is actually switching between two images extremely quickly, and each lens on the glasses switches between dark and clear so that the left eye only sees image 1, and the right eye only sees image 2. Let’s get that 100% clear: the left eye for all the viewers sees image 1 while the right eye is blanked out, then a fraction of a second later the left eye is blanked and the right eye sees image 2. Persistence of vision deals with the discontinuity in the images, just as it does with a regular TV.

That’s great… except that there isn’t a great deal of 3D content to watch at the moment. Most people will use their expensive new 3D TVs to watch predominantly 2D content for the time being. It seems a shame to waste all that image switching tech and LCD glasses… but perhaps there’s another use for technology: showing two different TV programmes at once.

Consider the following theoretical 3D TV: It has a single main remote control which has all the features you’ll never use, but comes with a second mini-remote which lets you change channels, select AV inputs, and adjust the volume of the second headphone socket. Second headphone socket? This imaginary TV has two separate headphone sockets, to go with the twin tuners that are built-in. The frames from one tuner or AV input are interlaced with the frames from the second, so that the TV is constantly switching between the two images at a high frequency.

The LCD glasses are also slightly modified with a 3-way switch to select between “3D”, “Programme 1” and “Programme 2”. This just changes the way in which they synchronise with the TV. In 3D mode they operate as described above, alternating between which eye is clear and which is dark. In the other two modes both eyes operate synchronously, so that both eyes see image 1, but are blanked from image 2 (or vice versa).

This setup means that two people can watch different programmes on the same TV at the same time by setting one pair of glasses to “Programme 1” and another to “Programme 2”, and donning a pair of headphones. It’s not hard to imagine a pair of kids playing a videogame, with the sound coming from the main speakers, while a parent or guardian watches a film using headphones. Want to check that the kids are playing something appropriate to their age? Just flick the switch on your glasses to see what they’re watching.

I have to admit that I haven’t used a pair of LCD shutter glasses, so I don’t know how much shadowing of the second image will be visible, but I would imagine it is likely to be acceptable for day-to-day use. It will probably also depend on the content – trying to watch a dark and moody horror film while the second programme is displaying a brightly coloured game will probably show more of a shadow than two images of similar brightness. But if it means being able to watch something different to your partner without having to become a social pariah, banished to “the spare room”, then it’s probably worth a little bit of ghosting.

Update, 22nd July 2010: It looks like someone at Sony had the same idea. Their patent was originally filed in 2006 though, so I can’t claim prior art.


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