3D TV FAQ: 2D answers to 3D questions

You've probably seen a 3D movie in the cinema, heard about the spangly new 3D TVs arriving this year, and may have even decided if you think the whole thing is worthwhile or not. But far from being new-fangled, 3D is as old as the hills. Well, as old as creatures with two eyes. So what makes the latest technology so exciting?

If you're still confused about what 3D is, how it works and how it's going to impact your living room, read our handy guide to all things in the third dimension.

How does 3D work?

3D vision in humans works by using our two eyes to see things from two slightly different angles. If you shut one eye, and try to pick something up from your desk, you might well find that it's a lot harder than with both eyes open. This is because the small distance between your eyes is what allows you to perceive depth.

In a TV, action happens on a single flat panel, with no depth information. So, to give the illusion of 3D, manufacturers use the skill of your brain in constructing 3D images from your two separate eyes to fool you into seeing 3D from their TVs. They do this by providing two slightly different perspectives to each eye, and getting your brain to turn that into 3D, in the same way it does with the real world.

What types of 3D TV are there?

There are two main types of 3D technology that are ready for you to use now. Commonly known as 'active' and 'passive', the two types deliver a similar effect, but have massive differences in the production cost, and how it is passed on to you, the consumer.

Active-shutter 3D is going to be the way most people end up seeing 3D in their homes. With this technology, the TV is basically the same as your current one, but with some increased performance to make the 3D look as good as possible. To see 3D, you'll need a special pair of glasses that contain a system that shuts off the light to first one eye, then the other.

While the glasses are blocking light to one eye, the TV is showing an image to the other eye, then the process switches, and the TV shows a separate image, shot at a slightly different angle, to your other eye. This synchronised shuttering basically provides a Full HD video stream for each eye, each very slightly different. Because your brain is translating two separate signals from your eyes all the time, it's fooled into seeing 3D.

The passive system, by contrast, uses a very simple set of glasses. These use circular polarisation to provide each of your eyes a different image from the same source. In cinemas, this works because two images are projected on to the screen in quick succession. They appear at a rate of 144Hz through a special filter that adds polarisation, alternating between the left and right eyes, 72Hz for each.

Translating the passive system for home use would produce much more expensive televisions. These would need to have a panel fitted in front of the LCD or plasma panel that alternated in time with the left and right images. LG is using this system in its 3D TV for pubs.

The cost of producing the glasses for polarised 3D screens is virtually zero, which is why you're sometimes allowed to keep the glasses after the movie ends. This is not true in Dolby 3D cinemas, which use a third system with moderately expensive glasses. As you can imagine, with active-shutter glasses being sold for £100 a pair, if a cinema were to use this system, it would kitting out its screens prohibitively expensive.

_{Polarised glasses are ideal for pubs and cinemas, because
they're cheap to produce.}

In terms of domestic 3D, there's only really one kind of 3D that hardware manufacturers are pushing, and that's active shutter. This system works for hardware companies because it's very cheap for them to implement. It doesn't add an awful lot to the cost of their TVs, because the glasses do most of the work. The consumer is expected to shell out the £100 or so, which keeps costs down for those people who don't want the 3D feature.

Which type of 3D TV is better?

For home use, active-shutter 3D is preferable for one main reason: resolution. Using this system, it's possible to get a full-resolution, 1080p image to the viewer for each of their eyes. With a polarised system at home, you would only see half the TV's 1080p resolution. This is because half of the 'lines' on the screen will be displaying the image for one eye, the other for the other eye. Although this wouldn't be ideal for Blu-ray, it works well enough for broadcast TV, which isn't currently in 1080p in this country anyway.

Sky 3D will be transmitted using a method called 'side by side 3D'. This system works by broadcasting the two different angles in one frame. It's called side by side because if you look at it on a normal TV, you'll see two images next to each other. This system ensures Sky's existing HD boxes are compatible with 3D, and a firmware update to the boxes will allow them to signal 3D TVs when they need to turn the two images into one.

Performance-wise, then, active shutter 3D is the better, higher-resolution technology. The downside is that the glasses are currently very expensive. Most manufacturers are saying each pair will cost £100 or more, which will be very expensive for families who want to sit down and watch a 3D movie together.

_{Sky is going to transmit its 3D in a mode known as 'side by side'.
In this system, the TV turns these images into one 3D picture.}

What TVs can I buy?

There aren't many 3D TVs on sale just yet. You can pre-order certain models, but soon the market will be awash with them.

Sony has two ranges that will be 3D-ready. Some of its TVs will be bundled with a couple of pairs of glasses and a transmitter to sync them. Others will require you to purchase glasses and a transmitter separately. Panasonic has one, high-end plasma that's ready for 3D out of the box. The 50-inch model is going to retail for around £2,000 and it will come with two pairs of glasses and the transmitter.

Samsung and LG are both bringing models to the market soon too. LG has a very high-end model, which looks stunning. Its Korean rival has a more sensibly priced, but still costly £1,800 model, known as the 40C7000.

Which is better for 3D: LCD or plasma?

The most important aspect of 3D is refresh rate. If your TV can't refresh its display quickly enough, you'll see a weird double image artefact. LCDs are slower than plasmas to refresh for the most part, so it stands to reason that, with shutter-based 3D systems, plasma would be the better technology to pair it with. Most people who have seen both working agree with this, but LCDs are getting faster all the time. New TVs with rates of 200Hz and higher will be more than good enough.

If you're hoping to use your existing TV for 3D, forget it. Although most modern screens probably could manage it in theory, you need the TV to sync to a pair of glasses. The only way to do that is to have a transmitter connected to the TV, and there's no way to do that with existing TVs.

Interestingly, demos of 3D TVs at CES this year made us think the best 3D panels might actually be OLED ones. Sadly these still haven't really started to appear on the market, so we're in for a wait.

What does 3D look like?

There are two approaches to producing 3D content. The first is the 'things coming out of the screen' method that's popular with horror and action movies, and certain animated features. This works as a pointy-pointy gimmick, but is annoying to watch for long periods and can be quite tiring.

The second approach is the 'box in your living room' style, where you peer into a 3D world with real depth. In this system 3D events don't come out of the screen, but happen behind it. So, watching a football match, you'd see action in the foreground, at the level of your screen. Then, behind that, you'll see the crowds in the stands as a background layer. This is a more natural technique, and suits smaller screens because the 3D illusion of things coming out of a screen is destroyed as soon as they hit the edge of the TV. This is much more obvious at home than it is in the cinema, because the screen doesn't fill your field of vision. A word of warning: you'll want to look away when Wayne Rooney celebrates a goal by kissing the TV camera.

How much are new glasses?

Most manufacturers are giving us estimated prices of £100 to £150 per pair for active-shutter glasses. We aren't entirely sure why they're so expensive, as the technology that powers them is reasonably simple. As more people buy them though, the price will fall. We hope that happens quickly, because families are going to find themselves spending a lot of money.

_{Active glasses, like these Sony models, will cost £100 or more.}

Will I be able to use Sony glasses, say, with a friend's Panasonic TV?

In theory: yes. In practice: maybe. The technology is the same for both systems, so the glasses could easily be interoperable. But there's no agreed standard at the moment, and the transmitters can use infrared to sync the shutters, or Bluetooth, or another technology altogether. Third parties are already offering glasses that will work with "any 3D TV", however. These, we're told, will cost $150 (£100) or so.

Is there any health risk?

It's too early to tell if there are long-term sight implications to 3D. The active-shutter system, however, could pose real problems to people with photo-sensitive epilepsy, as the rapid flickering could be an issue. The rate of refresh is similar to that of a 50Hz TV though, so it's quite unlikely we'll see any real problems.