A Beginner’s Guide to … 3D entertainment

The cinema and home-entertainment industries want to transport us to another dimension, but is it a journey worth taking? We investigate whether 3D is here to stay or just making another of its occasional comet-like passes.

If your idea of 3D is red and green glasses and the quick onset of headaches, it’s time to adjust your antenna. 3D technology has come on in leaps and bounds in recent years, the 3D effect is clearer and more convincing, the equipment is widespread in cinemas and becoming affordable for living rooms too. Meanwhile, film directors and other content creators are taking 3D more seriously than before, finding ways to use it as a storytelling tool rather than simply as a gimmick.

In this feature we’ll be looking at how 3D entertainment works, who’s producing it and what you’ll need to experience it in your home.

STEREO VISION

First, though, let’s talk about you. The chances are you have two eyes, which point in the same direction. Not everyone’s eyes do – one in fifty people have a condition called amblyopia, also known as a lazy eye. For them, the 3D revolution sadly isn’t going to have much impact.

The massive financial success of Avatar will ensure we see a lot more over the coming years, presuming your eyes are up to it.

People with normal eyesight have something called stereoscopic vision. The 6cm gap between our eyes means that each one sees the world from a slightly different point of view. Rather than perceiving a confusing double vision, our brains process the differences between the two images to create a mental model of the 3D space. This is called stereopsis. Another closely-related phenomenon is based on convergence. Hold a finger a couple of inches from your nose and you have to go cross-eyed to be able to focus on it. Look at something far away and your eyes can relax and point dead ahead.

The brain intuitively uses stereopsis and convergence to judge distances with impressive accuracy. However, people who have one blind or lazy eye are still perfectly able to navigate the world around them. That’s because stereopsis and convergence are just two of many techniques humans use to perceive distances. Our innate understanding of perspective is just as important. We also know what size various things should be so if a house appears very small, or an ant is very big, this tells us how far away it must be.

A TV, PC, projector or cinema screen is essentially flat, but even when we’re watching normal 2D footage we choose to ignore its flatness when viewing a picture that simulates a 3D world, such as a film. It’s not hard, because the image is packed with clues to help us understand the 3D space it attempts to simulate: perspective, familiar sizes and so on.

We can get caught up in the excitement of a horror film, but we don’t really believe that the on-screen monster is about to burst through the screen and terrorise the audience. It was different for the first people ever to attend the cinema in 1895, though. They famously fled the building for fear of being run over by the train that loomed before them on the screen.

Today, 3D cinema sounds echoes of this historic event. Dennis Laws, Technical & General Manager at the BFI Imax in London, describes the reaction to the animated short film Paint Misbehavin’, where “the entire audience is trying to catch these globules of paint which appear right in front of their noses.” The 3D effect is not only so convincing but also so unexpected that viewers struggle to believe that’s just an illusion.

That illusion works when a screen is able to transmit different images to the left and right eyes. With control over what each eye sees, it’s possible to simulate the stereoscopic effects – stereopsis and convergence – by offsetting the viewpoint of one eye compared to the other.

CINEMATIC DEPTH

The theory behind 3D visuals is fairly simple but it’s not so easy in practice. First, you need two discrete images that interact in a meaningful way to create a 3D effect. Then you need a system that sends each image to the correct eye and that eye only.

Classic anaglyph glasses, great if you don’t mind watching in blue and red

Cinemas have experimented with various techniques over the years. The most memorable one for most people will be the anaglyph approach with its distinctive red and green glasses. This works because a red line will look red through the red filter, but black through the green filter. A green line has the opposite effect. This makes it easy to separate the left-eye and right-eye images, simply by converting them to monochrome green and red images. No special projector is required and the glasses are cheap.

The downside is that the picture is in monochrome, and not even a simple greyscale. The fact that each eye sees different colours is distracting, and some people find it fatiguing or headache inducing. Full-colour anaglyph techniques have been developed, but in truth they’re only partly full-colour and partly 3D.

Another technique that has been tried in cinemas is to use battery-powered glasses that use LCD shutters to block the light to each eye in turn. The timing of the alternating lenses was synchronised with frames on the screen, so when the projector flashed up a frame for the left eye followed by a frame for the right eye, only the correct eye saw each image.

This gave a full-colour 3D image and a convincing 3D effect, but the alternating shutters could be distracting. They weren’t comfortable to wear, either, resembling a futuristic welder’s mask. Because the technology was built into the glasses, it was expensive to equip each person in the theatre, so it’s not surprising that this approach never caught on in cinemas.

POLAR EXTREMES

By far the most enduring technique in cinemas is polarisation. This works on the principle that light is a wave, oscillating at right angles to its direction of travel. A polarising filter can absorb light rays that oscillate up and down, while letting through rays that oscillate left to right. Rotate the filter by 90 degrees and it has the opposite effect.

Polarised glasses, the most common way to see 3D at the cinema today

By using two carefully aligned projectors and fitting a vertically polarised filter to one and a horizontally polarised filter to the other – and equipping the audience with corresponding polarised glasses – a full-colour 3D effect is created. Despite the iconic status of those red and green anaglyph glasses, it was actually polarisation that was most widespread in the 3D cinema booms of the 1950s and 1980s.

The main projector at BFI Imax, Waterloo, uses this long-established technology. It’s essentially two projectors in one, with separate reels of film for each eye. They pass through two projectors, each one having been fitted with a polarising filter that corresponds to the filters in the glasses worn by the audience. Not all 3D films are distributed in Imax 3D but the biggest blockbusters generally are, as well as films made exclusively for Imax.

Inevitably there are downsides to the polarisation technique. One is that a silver rather than white screen is required to maintain the polarisation as light bounces off the screen. That also means a brighter picture for those sitting in the best seats, but a considerably darker one for those sitting at the sides. If you’re watching a 3D film in the cinema, or even watching a 2D film on a screen that’s designed for 3D, be sure to get a good seat.

Another problem is that the two projectors must be aligned perfectly and in sync to avoid the 3D effect going disastrously wrong. Even with careful alignment film can jitter, whereby the picture moves up and down very slightly on the screen. These problems aren’t easy to overcome, and were particularly tricky to handle in the 1950s and 1980s, and they’re further reasons why 3D cinema is associated with headaches. It explains why Imax cinemas, with their highly specialised equipment and staff, were the only ones to keep 3D cinema alive throughout the 1990s and 2000s.

Imax 3D uses over 10 miles of film for each eye for a 150-minute film

The third boom in 3D cinema that’s happening now is largely down to the convenience of digital projection. Rather than grappling with twin projectors, cinemas that use the RealD system – which is most 3D screens in the UK – receive films on a 500GB hard disk that plugs into to a single DLP projector. An active polarising filter in front of the projector’s lens uses liquid crystals to change polarity 144 times per second – that’s six times the speed of 24fps film. Each frame is shown six times, alternating between the left-eye and right-eye images to avoid perceptible flicker.

Another difference between Imax and RealD 3D systems is that RealD uses circularly polarised filters. Rather than filtering the light on vertical and horizontal plains, it’s filtered in clockwise and anti-clockwise twisting motion, like a corkscrew. The advantage of this technique is that it still works when viewers tilt their heads. In an Imax 3D film, it’s important to keep your head straight or else the polarising glasses become ineffective. Neither system is perfect, though, and there will always be some ghosting in polarised systems where a little of the left-eye image reaches the right eye, and vice versa. It’s most noticeable in high-contrast lines such as title sequences and end credits, but pale faces against a dark background can also suffer this problem, and it can be quite distracting.

Digital cinema projectors are certainly more convenient than dual film projectors, but they’re not as bright or as detailed. The Odeon chain installed NEC NC1600C digital projectors in its cinemas back in 2009, but its 17,000-lumen brightness and 2,048×1,080 resolution means it’s only suitable for small and medium-sized screens, especially because polarisation halves the amount of light projected. NEC’s latest NC2500S projector is rated at 26,000 lumens, and Sony’s SRX-T110 has a 4,096×2,160 resolution, but compare these to the 60,000-lumen brightness of dual Imax projectors and the theoretical resolution of 12,000×8,700 of its enormous film frames, and it’s easy to see why Imax still claims to offer the best 3D cinema experience available.

COMING TO A SCREEN NEAR YOU

The cinema industry is clearly revelling in the public’s newfound enthusiasm for 3D, convincing people to go to the cinema for the full 3D experience rather than wait for the DVD and Blu-ray releases. The home-entertainment industry hasn’t taken long to catch up, though, with all the major TV manufacturers now selling 3D TVs. The movies to go with all this new home 3D kit have been slower to arrive, however.

Most of them, including Panasonic, Philips, Samsung, Sony and Toshiba, are using LCD shutter technology. Thanks to the fast refresh rates of existing plasma (and many LCD) TVs, it’s not much of a technological leap to synchronise the TV with shutter glasses, with both running at a fast frame rate to eliminate discernible flicker.

Active shutter glasses work well, but are expensive and need recharging occasionally

The glasses are much more stylish than the heavy-duty visors once used in cinemas, and only a little bulkier than the passive, polarised glasses you probably wore to watch Avatar. They’re still expensive to buy, though, costing up to £100 a pair. At first manufacturers bundled a pair or two with each set; but with 3D becoming a more common feature on high-end models, and prices getting more competitive, many manufacturers are opting to keep the price of the TVs down and sell the glasses as optional extras instead.

JVC has opted to use polarisation in its 3D TVs, while LG and Toshiba have a foot in both camps with both polarised and ne active shutter TVs in this year’s models. Because polarised glasses are cheap, the chances are that these TVs will find favour among pubs and bars showing sports events, and also with large families and anyone who’s looking forward to inviting their friends over to watch 3D TV. Bear in mind that, without enough glasses to go round, 3D TV is unwatchable because of the double image.

It’s too early to say for sure, but it looks like TVs using active shutter glasses will produce a better picture than the ones using polarisation. This is partly down to the ghosting that polarised systems exhibit, which is a problem not shared by active shutter systems. The other reason is that the resolution of polarised TVs is effectively halved when showing 3D content.

Without the glasses, the TV shows a Full HD 1920×1080 picture. However, when viewed through polarised glasses, the picture is split, usually per horizontal line, so that all the odd lines go only to the left eye, and the even lines, only to the right eye. As such, each eye sees a 1920×540 picture. Active shutter glasses, on the other hand, show the left eye a complete 1920×1080 picture, and then the right eye another 1920×1080 picture.

That said, a new technology, from RealD who designed the system in cinemas is coming. This is best described as active polarisation, with the screen actively switching between differing polarised images. The idea is to get the full screen resolution with cheap polarised glasses – though we’re yet to see it working in practice.

JUST BE CONTENT

None of these 3D TVs are much use without 3D content to show on them, and that’s been slow coming. Sky’s 3D channel, appropriately named Sky 3D is available to subscribers of its HD packages, although it won’t add anything to their bills. A quick glance this week shows that content is largely limited to sports, animated movies and music and dance programmes. Victoria Etaghene, Consumer PR for Sky told us, “As more content is available for the channel we may look to change the way we offer it to customers.”

Football fans in Cardiff getting a preview of Sky’s 3D sports channel

Sky first unveiled its technology back in January 2010 when it broadcast live coverage of the Arsenal versus Manchester United football match to nine pubs around the UK. We’ve had a number of chances to view the service since then, and although football in 3D doesn’t immerse you in the same way as it does at a cinema, the effect is convincing. Shots from the stadium terrace give the impression of being there in person, and views from the touchline provide an amazing sense of perspective.

Sky has had to find a way to broadcast its 3D service using its existing satellite network and Sky+HD set-top boxes. Dual TV cameras capture a pair of images, but these are squashed so they fit side by side in a normal 1920×1080 HD signal. This passes all the way to the TV, whereupon the 3D TV expands and overlays the left-eye and right-eye images to show on the screen for the 3D-bespectacled viewer. This means that the resolution is halved to 960×1080, but that’s a fair price for not needing a new set-top box or a change to the Sky infrastructure.

If you’ve tried watching 3D TV in a pub, then the chances are the screen will use polarisation, halving the resolution that reaches your eyes. Factor this with Sky’s 960×1080 broadcast, and you’re left with a 960×520 picture for each eye – just a quarter the resolution of 1080p Full HD. So if the details were a little soft then you’ll know why. Thankfully, the benefit of 3D effect is far more significant, and TVs that use active shutter glasses can display Sky 3D’s 960×1080 broadcast without wasting any detail.

BLU MOVIE

Another important development for 3D home entertainment was the ratification of the Blu-ray 3D format back in December 2009. Discs use a codec called Multiview Video Coding (MVC), which is an extension of the H.264 codec used on standard Blu-ray discs. MVC carries separate 1920×1080 frames for the left and right eyes with only a 50 per cent overhead compared to a normal Blu-ray picture. Blu-ray 3D discs still play in older Blu-ray players, simply by ignoring the right-eye picture and showing a 2D image of the left-eye picture.

The HDMI cable must carry twice as much data for 3D, though: 1920×1080 at 48fps for a 3D film that runs at 24fps. Fortunately HDMI 1.4 allows frame rates up to 60fps at 1920×1080, so HDMI 1.4 should be supported on all 3D-capable TVs and Blu-ray players.

Avatar on 3D Blu-ray is still on limited release, and only available with certain hardware

Blu-ray 3D players are now widely available, but discs are still very thin on the ground. This is because it has taken a while for Hollywood to gear up for the additional hassle and cost of 3D movie production. For ages, that limited 3D releases to those you’ve seen at the cinema: the usual rash of easy to convert 3D animations, plus movies that were shot in 2D and had 3D elements added afterwards (such as Clash of the Titans). Now, though, major blockbusters are all coming in original 3D, and the Blu-ray’s of those will follow quickly.

Pirates of the Caribbean: On Stranger Tides may lead the charge for live action films on Blu-ray 3D

3D ON YOUR PC

The computer industry was ahead of the consumer electronics giants in bringing 3D to people’s homes. Back in 2008, we reviewed the Zalman ZM-M220W, a 22in LCD monitor with a polarising filter and Nvidia graphics card support to provide a 3D gaming experience. The list of supported games wasn’t huge but it gave us an exciting taste of 3D gaming’s potential.

Until recently, Nvidia’s 3D Vision system dominated the 3D PC market. It comprises a pair of LCD shutter glasses and an infrared transmitter to sync the glasses up with the picture. It also requires a compatible Nvidia graphics card and monitor. All the latest cards are supported, although it’ll need to be pretty powerful to generate two simultaneous video streams. Thanks to the way DirectX leaves rendering of game visuals to the graphics card, Nvidia is able to create the 3D effect for a long list of existing PC game titles.

The latest PC graphics cards, such as this AMD Radeon HD 6950, support 3D via their HDMI 1.4a outputs

This approach is bound to fade away soon though, with the latest cards from both Nvidia and AMD supporting the home cinema HDMI 1.4a standard. This will bring 3D gaming and movie playback on PCs in line with the latest TVs and Blu-ray players.

A 3D FUTURE?

Projector manufacturers are looking to join in the 3D home entertainment boom. A good thing, as we’ve found that a big screen is by far the best way to experience 3D, so a projector makes more sense than a medium-sized TV, and it’s far more affordable than a massive TV. The high refresh rate of DLP devices makes them more suitable at present, and you can add 3D to some existing models using the clever Optoma 3D-XL. We’re still waiting on affordable LCD-based models for home use.

It may look bland, but the Optoma 3D-XL can add 3D punch to existing projectors

TV manufacturers are making 3D a standard feature on high-end TVs this year, and probably on most mid-range models by the year after. It’s hard to see whether active shutter will win out over polarised, though we think the latter is far better bet for watching the occasional big event or movie with family and friends.

It’s also hard to judge how popular it will be, as its take up is driven by the availability and desirability of the content as much as the cost of the TVs. At the end of the day, as long as the content producers use 3D to enhance a story or event, rather than as a showboating gimmick, then we should look forward to 3D entertainment for years to come.

On the next two pages we look at how 3D content is created and how movie studios can make viewing 3D a more comfortable experience

FIRING ON BOTH LENSES: CREATING 3D CONTENT

The illusion of 3D on a flat screen is only possible if the content is in 3D. One way to achieve it is to use two cameras side by side, one capturing the left-eye image and the other for the right eye. That’s easier said than done, though. Professional cameras are big, so it’s often hard or impossible to get them close enough to simulate the 6cm typical distance between humans’ eyes.

Imax’s custom-designed 3D film camera weighs over 100kg, making it extremely difficult to manoeuvre. Sky’s early experiments with 3D capture involved mounting one of the two cameras vertically, facing a mirror. The stop-motion feature film Coraline (2009) just used one camera, and for every frame it had to be shuttled across to capture an image for each eye. Even when it is possible to mount two cameras side by side, there are problems with keeping their settings and frame rates perfectly in sync.

Panasonic’s compact AG-3DA1 broadcast camera

Fortunately, digital technology has come to the rescue. Panasonic broke ground with its AG-3DA1, a dual-lens, dual-sensor HD video camera aimed at the TV broadcast market. And now there’s even 3D digital cameras and camcorders aimed at consumers, such as the Fujifilm FinePix Real 3D W3 and the Panasonic HDC-SD90 with its optional 3D lens. For a cheaper option, even the Nintendo 3DS can take 3D images and show them on its glasses-free display.

One of Fujifilm’s range of 3D cameras, complete with 3D display on the rear

Computer-animated films such as Monsters vs Aliens are relatively easy to produce in 3D. Because the actors, sets and camera are all virtual, no extra technology is required to produce two points of view a few virtual centimetres apart. Pixar was even able to go back to the original animation data for Toy Story and Toy Story 2 and render them again in 3D for a new theatrical release in 2009.

Converting existing live-action films from 2D to 3D is much harder because the depth information must be added manually, but it has been done. Special effects experts Industrial Light and Magic produced a 3D version of The Nightmare Before Christmas in 2006, 13 years after the original was released. Meanwhile, after the success of 3D spectacles such as Avatar, Warner Bros decided to re-master two of its big films for 2010 (Clash of the Titans and the latest Harry Potter film) for 3D, even though both were shot using normal cameras.

3D games designers have the easiest ride, as not only are the graphics created in a virtual environment, but that environment is generated in real time as the game is being played. Because of the way DirectX works, games don’t even have to support 3D explicitly because it’s the graphics card’s job to turn the 3D geometry, textures and lighting into images on the screen.

MAJOR HEADACHES: IS 3D A COMFORTABLE VIEWING EXPERIENCE?

3D cinema has often been criticised for being hard work to watch, and even for causing headaches and seasickness. If that was once true, our experiences of recent 3D footage haven’t backed it up. This might be partly down to improvements in the technology. Polarised and LCD shutter glasses give a full colour image that doesn’t have the distracting colour-offset issues of anaglyph’s red and green glasses. Meanwhile, digital projection eliminates problems concerning keeping two film projectors in perfect synchronisation.

Just as significantly, directors are refining the way they use 3D. Daniel Glennon, Assistant Marketing Manager at Odeon, commented: “What’s exciting is that 3D is being used in so many different ways by different filmmakers. From the likes of Final Destination, where 3D is used to ‘throw’ items at the screen in the same way as 3D was used in the 1950s and 1980s, to Up, where 3D is used to add depth to a beautifully constructed tale. James Cameron is a real pioneer in the field and Avatar uses 3D to literally immerse the audience in another world.”

Pixar’s Up took a subtler approach to 3D, placing everything behind the screen and nothing jumping out

Dennis Laws at the BFI Imax sees filmmakers increasingly using gentler forms of 3D. “In reality, although we walk around in a 3D world, we don’t have things breaking into our own space. That’s done as a gimmick. It’s fun… but you don’t need to do it all the way through the movie.”

John Dollin, Senior Product Development Manager for Sky 3D, showed us footage of Sky’s first tests in 3D. “In the early days, we were still learning how to shoot 3D”, he commented. “The 3D effect was certainly visible but camera angles changed too quickly for our liking, and moving camera shots sometimes spoiled the illusion. However, later tests were done with the help of Vince Pace, Director of Photography for Avatar. The later footage was much more comfortable to watch, and really conjured up the feeling that we were at a live event.”