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Broadcasting
Has 3D TV come of age?
Valery Timofeev
photo credit: ITU/V. Martin
Christoph Dosch
Chairman of ITU–R
Study Group 6
Valery Timofeev
photo credit: D. Wood
David Wood
Chairman of ITU–R
Working Party 6C
   
image
Photo credit: AFP
 

Everyone wants to know: is three-dimensional television (3D TV) just a fashion that comes and goes like a spring clothing collection? That is rather how it has been regarded before — more than once. About every 25 years, since the beginning of the twentieth century, 3D catches the public (and business) imagination. Each time its star fades. But each time its secrets are kept alive by enthusiasts.

Will it be different this time? Will the technology be able to permanently win audiences for television, spurred on by successful 3D movies, and starting from 3D pay-television in the coming months? Plans have been announced for broadcast 3D television services in several parts of the world. Major sporting events, such as the 2010 FIFA World Cup in South Africa and the 2012 Summer Olympic Games in London, will include 3D television coverage, heightening the public’s appetite for this new viewing experience.

There are indications that, if ever 3D TV was going to succeed, now is the time. A confluence of factors means that the quality of 3D TV is going to be higher than was ever possible before. But with a history of “boom and bust”, and arguably with some eye fatigue issues still unresolved, is this the time for the viewer or industry to invest in 3D TV? The answer is that no one knows for sure, but success or failure in agreeing common technical standards will play a part.

ITU’s Radiocommunication Sector (ITU–R) has a track record of agreeing standards (“Recommendations”) for television formats. These have made possible digital television and high-definition television (HDTV). Everyone has won because of the common standards, and it would be great if we could do the same for 3D TV. Whether it becomes ubiquitous or just used for special events, 3D TV will succeed if it is based on common standards — but will lose if the marketplace is fragmented.

The job may not be simple. It is increasingly difficult to agree on common standards today because research and development is more often done by commercial industry that can have different objectives from those of public bodies. There are open source initiatives (though not for 3D TV) which produce wonderful results but can make us forget that common standards do not just happen by themselves. The number of alternative implementations of 3D TV is large. And of course, as usual, everyone wants a common standard — as long as it is theirs.

Finally, we must remember that some ITU Recommendations can take time to be agreed. But time is something we may not have with 3D TV, as some broadcast 3D services will start later this year. Whether we succeed will depend partly on the leadership shown in ITU–R, but mainly on the will of national administrations and industry to make proposals for draft Recommendations to ITU–R’s Study Group 6 (which examines broadcasting services), and to compromise if needed, at upcoming meetings.

The basics of 3D TV

   
Valery Timofeev
Photo credit: ITU/V. Martin
“The new ITU report on 3D TV establishes a clear framework for the development of new types of systems that will change the way we experience broadcast and multimedia content.”
Valery Timofeev, Director of ITU’s Radiocommunication Bureau
 

The basic principle of 3D TV is the same as it has always been. Two pictures (one for the left eye and one for right) are superimposed on the same screen, and a mechanism (that usually involves the viewer wearing special glasses) makes sure each eye sees the correct picture. It is similar to the process of natural human vision — but not totally. In today’s first-generation approaches to 3D TV, the viewer does see depth in the picture (through interocular parallax), but there are some additional complications.

The physics behind the difference from natural vision is that the phase of the light wave originating from the object being photographed is not recorded by a 3D camera, just the amplitude of the wave. It is the phase information which normally guides the eye’s focus. This leads to something scientists call a potential “accommodation-convergence” conflict, which can strain your eyes. Thus the “missing” part of the light wave can be the cause of eye fatigue, unless you are very careful with the way you shoot and watch the pictures. The need to take so much care is why the recently released 3D movie “Avatar” took so many years, and cost hundreds of millions of dollars, to make.

Production challenges

Applying that care in television will have a major impact on the success or failure of 3D TV. There are rules which amount to a “grammar” for making 3D TV programmes, but they are outside the domain of technical standards. Special new 3D cameras and processing equipment are needed to make 3D programmes.

A number of recent trial 3D TV productions have provided useful lessons. And more knowledge will be gained through ongoing trial productions. Many aspects of production will need a rethink, including training. For example, 3D cameras have to be placed close to what they are shooting. Another new element is that an additional post-production stage will be needed to register, align, and manipulate the left and right pictures as a pair. There will be a whole new market for such processing equipment.

There is no single standardized format for contributing, distributing or archiving material in a 3D television studio. This is also the situation for HDTV — there are about forty different ways to make an HDTV programme today, when you take into account all the combinations available. Should ITU–R play a role in generating Recommendations for 3D television production formats? Manufacturers and administrations will decide, by way of their contributions to ITU–R Study Group 6 and its Working Party 6C.

3D displays

Over the last year, many of the world’s display manufacturers announced that they will make 3D TV displays. This move has been seen as an effort to boost sales now that profits from flat screens and HDTV sets could be levelling off.

Will the 3D television sets cost a lot more than usual ones? In reality, the extra cost to the manufacturer of making a 3D version of an existing display should be modest. They might, for example, simply need to add a way to switch to the right and left lenses of special glasses with each frame of the picture (in the active shutter system). Or it might mean adding a coating over the screen to make left and right pictures give out light with alternate polarizations (in the polarization plane system). Most of the 3D sets seen recently at trade fairs and exhibitions have featured plasma displays with shutter glasses.

While there may be only moderate additional costs, most manufacturers plan to start with “high end” 3D TV displays. This minimizes their risk, because they do not have to invest too much. But this, by the way, maximizes the broadcaster’s risk because the initial audiences are bound to be small. However, one manufacturer looks like being the exception and is going for high volume from the start. This is because their many millions of games machines can be upgraded to 3D TV, and to harvest this market, they need to have corresponding millions of 3D displays in the customers’ hands.

Broadcasting 3D TV

For some time, there has been a free-for-all of ideas about ways to exchange programmes and broadcast 3D TV. Now the smoke is clearing, and a pattern for ways of broadcasting 3D TV is emerging. This is one of the key elements of the ITU–R Report agreed by Study Group 6 in November 2009. The new report provides a map for future 3D TV.

 
image
Photo credit: D. Wood
The first 3D TV programmes were made in Germany in 1982 by the broadcaster NDR. The picture shows a 3D production being made at a zoo in the Netherlands

First-generation 3D TV

Broadcasting is, arguably, the area where standardization is most valuable. It directly affects the largest cost and most influential element of any broadcasting system — the price and quality of the home receiver.

The ways of broadcasting 3D TV are likely to evolve over time, as described in the report. Today, what we have are the elements of “first-generation” 3D TV technology: the Plano-stereoscopic systems.

The need to study health implications and eye fatigue

3D can work very well, and has a real "wow" factor, but a fundamental part of the way 3D TV works brings the risk of eye fatigue. It seems that people may find they "see double" and need to take off the special glasses when they watch 3D. But this is anecdotal evidence or "single case studies", rather than extensive and controlled scientific evidence. What we need is a thorough study of the causes and effects of eye fatigue associated with 3D TV, including potential harm to children.

 

With these systems, wearing special glasses similar to those used to watch 3D cinema, viewers will be able to see depth in the picture, and as in the cinema, the view will remain the same when they move their heads (in real life, our view changes when we move our heads), and accommodation-convergence may arise with its potential for eye strain.

The extent to which the viewer will need to buy new home equipment to watch programmes in 3D can be divided into four levels.

Compatibility levels

With a “Level 1” system, the viewer does not need to buy new equipment, and will enjoy limited 3D experience using today’s standard HDTV set. The system converts the left and right signals into two pictures, each with a different colour cast. These are mixed and broadcast together. Standard HDTV sets receive these “anaglyph” pictures, and viewers use glasses with different colour lenses corresponding to the colour casts to provide each eye with the correct picture.

With this kind of system, it is difficult to achieve entirely correct colours or to prevent “cross talk” between the pictures. It has been used for broadcasts in the United States and Europe (such as Channel 4 in the United Kingdom). In any event, we do not need to standardize this level because existing television signals and sets are used unchanged.

A “Level 2” system needs a new display but no new set-top box. It is known as a “frame compatible” system. It allows a 3D picture to pass through an existing set-top box like a normal HDTV picture. New electronics in the display then unravel the frame compatible signal and create the left and right pictures for showing on the screen. The additional cost to a 3D display to do this is likely to be modest. However, in creating the combined broadcast signal, some resolution may be lost from the individual left and right signals.

There are several different ways of creating a frame compatible signal, each with different strengths, and some with licences and others without. It is believed that those pioneering 3D TV services, starting this year, plan to use a format called “side-by-side” or SbS. Could ITU–R delegates agree on a single Level 2 format — SbS or something else? We await proposals. What bit-rate will the side-by-side frame compatible signal require? One of the users suggests it will be about their “normal sports bit-rate” for HDTV, which is 16–18Mbit/s.

 
image
Photo credit: AFP
A prototype model of a 3D TV plasma display panel expected on the market in 2010

“Level 3” would be a Level 2 signal with an additional “top-up” signal, to bring the resolution of the two left and right pictures up to 2D high-definition quality.

“Level 4” needs both a new set-top box and a new display. The broadcast signal includes a 2D picture which can be seen on a normal set, plus an extra signal in the multiplex that can be combined with the 2D signal to create the left and right pair in the new set-top box. This is a “2D plus something” or a “2D service compatible” system. The “something” can be created in a number of different ways, some open and some proprietary. The simplest form of the “something” signal would be the second full picture itself.

Another way is to use a system called multi-view coding (MVC) that was developed by the Joint Video Team (JVT) formed from experts in Study Group 16 of ITU’s Telecommunication Standardization Sector (ITU–T) and the Moving Picture Experts Group (MPEG) established by the International Organization for Standardization (ISO). MVC can be used for a left and right system, or it can be used for future systems where there are multiple pairs of signals available.

The Blu-ray Disc Association has chosen this MVC format for 3D Blu-ray discs, and it will succeed the anaglyph formats in Blu-rays later in 2010. How much bit-rate will it need? The Blu-Ray Disc Association are understood to be thinking of a total advanced video coding (AVC) bit-rate of up to about 30–36 Mbit/s, with 16–20 Mbit/s for the base 2D signal and an additional 60–80 per cent of that for the “plus something” MVC channel.

A “Level 4” system could also be a choice for free-to-air 3D TV broadcasters, because there are no service-linked set-top boxes to cater for. Viewers would still be able to watch a picture on normal television sets. However, if a frame compatible system is used for terrestrial broadcasting, it might not be easy to find the additional channels for simulcasting 3D TV channels in 2D.

Whatever system is used, we should ask now whether we are “locking out” 3D TV from the terrestrial bands unless we ask for more spectrum for broadcasting today.

What will come in future?

Two or three future generations of 3D TV can be imagined — though they are not certain. The first would follow the arrival of a multiview auto-stereoscopic display and would allow viewing in 3D without the need to wear special glasses. It would also provide the viewer with multiple 3D pairs of views — but how many views would be needed? What resolution would the display need? How would multiview programmes be produced? These are all unknowns today.

A generation beyond this may see systems with large numbers of vertical and horizontal views. This is approximately how insects see with their compound eyes, and is sometimes called “holoscopic” (mixing the words holographic and stereoscopic) or ”integral” television.

The job to be done today

These possibilities will be topics of discussion for future generations of delegates at ITU meetings. Today, our main preoccupation must be to convince industry to submit draft Recommendations for a common broadcast format for both the frame compatible case and the service compatible case. Administrations must encourage industry to do so. This could be the “make or break” element for 3D TV.

 

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