Three-dimensional displays: Getting rid of the glasses
By Tom Metcalfe
The new wave of 3D movies is on the ebb. James Cameron’s Avatar in 2009 sparked popular interest and commercial investment in 3D content and technology, and offered the film industry new hope at a time when box office receipts for regular movies were falling. In 2008, 3D was used in less than three percent of all movies, but after the success of Avatar that figure jumped to 16 per cent of movies made in 2009, and 31 percent of movies made in 2010.
Now analysts see the beginnings of an audience backlash. Although global revenue from 3D movies hit a record US$6.9 billion dollars in 2011 in North America, the largest 3D market – box office takings fell from US$2.1 billion in 2010 to $1.9 billion. The analysts say North American movie audiences are suffering 3D-fatigue after a recent spate of poor quality 3D movies – especially some movies shot in 2D and post-processed to 3D – and are becoming more selective about what they see. The number of 3D productions has also fallen in the two years since the post-Avatar peak.
On the other hand, several native 3D movies like Hugo, Prometheus and The Amazing Spider Man have been popular hits, while Avatar remains the highest ever grossing movie, in any number of visual dimensions. In 2012, Cameron’s Titanic-3D showed that 2D movies post-processed with sufficient care (and money: Cameron re-shot parts of several scenes for the 3D adaption) could also be successful.
But even if the glamour of 3D fades a little on the big screen, modern 3D display technology is now making a splash on the small screen in flat-panel televisions, computer displays, smart phones, cameras and gaming handsets. The digital 3D technology that made the effects of Avatar possible is being miniaturized, along with everything else. A recent study estimated that 3D displays were available on more than 23 million devices in 2011 – and while the number of 3D movie screens is forecast to grow at around 16 percent a year worldwide, the number of 3D displays on mobile devices is expected to grow at 190 per cent per year.
Watching movies and playing games are the most popular 3D applications, but 3D has also proved its worth in sports broadcasts like the 2010 World Cup football games in South Africa, and for live concert recordings. User-created 3D content is popular on video-sharing websites like YouTube, and websites can now feature “in-depth” 3D views of a new car or new house.
3D display technology has also been put to new applications that take advantage of the presentation of depth information, such as industrial design and 3D modeling, terrain mapping, medical research and surgical practice, scientific and pharmaceutical research into the shapes of complex molecules, and astronomical visualizations. 3D displays have been used in airport x-ray scanners to give security staff a better view of the inside of passengers’ luggage, and a variation of stereoscopic 3D technology is used in some car navigation systems to let the driver see a GPS map while their passengers watch a movie on the same dashboard screen. Industry watchers say the wide availability of 3D displays and software will aid the development of new applications, such as “augmented reality” devices like Google’s “Project Glass”.
Stereoscopic-3D – the display technology used in modern 3D movies and on flat-screen 3D televisions – is really just a trick of the light. The resulting illusion is not true 3D, like a laser-generated hologram that can be viewed from any angle, but a sort of a “two-and-a-half-D”, visible only in a relatively narrow angle in front of the screen. Although modern technology has done much to improve the quality of the image and broaden the viewing angle, today’s stereoscopic 3D (S3D) movie theatres and displays use basically the same principle as the “stereogram” photographs popular in the 19th century.
The differences in the images trick the eyes to converge at different distances when they view the scene, which the brain interprets as an illusion of depth. This is why 3D movie-goers have to wear glasses with some sort of filters in the lenses - to separate the combined screen image into separate images for the left and right eye.
Stereoscopic images fool the eye and brain by presenting slightly different views of the same scene to each eye. The differences in the images trick the eyes to converge at different distances when they view the scene, which the brain interprets as an illusion of depth. This is why 3D movie-goers have to wear glasses with some sort of filters in the lenses – to separate the combined screen image into separate images for the left and right eye. Some older 3D movies used a technique known as anaglyphy, with the superimposed images filtered by colored lenses. Most 3D movie theatres and theme park attractions now use a system based on polarized light, in which the separate images for the left and right eyes are split by polarizing filters in the glasses.
Some movie theaters, 3D television systems and gaming devices achieve the effect by using “active” electronic glasses, which filter the screen image with liquid crystal polarizers or shutters for each eye. Alternative big-screen S3D systems include Dolby 3D, which superimposes left and right eye images in specific wavelengths of red, green and blue light for each eye. The Dolby 3D system produces a brighter image than polarizing S3D systems and eliminates the need for a highly-reflective silver screen, but lenses of the Dolby glasses contain precision interference filters that are much more expensive than polarizing lenses.
Regardless of the method used, all stereoscopic-3D images suffer from a particular limitation, quite apart from the inconvenience and sometimes unfashionable appearance of the glasses. The stereoscopic trick only works if the viewer’s eye is focused on the movie or display screen. But at the same time, the stereoscopic effect forces the viewer’s eyes to converge at a point in front or behind the screen, to give the illusion of depth. In real life, however, our eyes always converge and focus on the same thing. While it is possible for our eyes to converge and focus at different distances, the effort has been described as like trying to pat your head and rub your belly at the same time. It is this convergence problem that causes eyestrain and tiredness in some 3D movie-goers, and it can be particularly bad in some 2D movies that have been re-released as 3D.
Convergence is an insurmountable problem with stereoscopic 3D, and the best that movie directors and audiences can hope for is to ease the problem with careful visual design. In the best cases, like Avatar or Prometheus, the technical problem of convergence is considered at the outset of the production, and influences the set design, scene direction and cinematography. Fast shot changes are kept to a minimum, so viewers’ eyes have time to adjust to the convergence in each new scene, and the composition of depth in each scene is kept relatively simple.
Although the convergence problem is unsolvable, several S3D display makers have at least shown progress in getting rid of the glasses. Like stereoscopy, which harks back to 19th century stereograms, autostereoscopic 3D – that is, 3D without the glasses – has a rich history. A primitive type of autostereoscopic 3D, which used a faceted screen to show different images to the left and right eyes of the audience, was used in several short films in the Soviet Union in the 1940s, and in a 1946 feature film titled Robinzon Kruzo. The new versions of this venerable technology use either layered liquid-crystal displays or an array of lenses on the surface of a single display as a “parallax barrier” to create the 3D effect without the use of filtering glasses.
Early versions of the technology required the viewer to maintain a specific distance and position relative to the screen, as even a slight change in the arrangement would break the 3D effect. That is not such a serious problem on single-user computer displays or portable gaming handsets. But autostereoscopy is more difficult to apply to 3D television sets that will be watched by several people from different viewing angles – or to hundreds of people in a movie theater.
Experimental methods to expand the viewing angle of autostereoscopic images include combining a 3D display with a camera and face recognition software, to provide a custom-made 3D image for each viewer, depending on where they sit. A research team at Microsoft has demonstrated a 3D display that uses face recognition to project a 3D image to up to four people at once, and Singapore firm Sunny Ocean is developing a 3D screen visible from 64 individual reference points. Toshiba is working on an ultra-high definition LCD display that combines nine different pairs of autostereoscopic images to create a display, which gives a horizontal viewing angle of 30 degrees.
Rochester NY-based Dimension Technologies, a NASA contractor and one of the major patent holders in the 3D display industry, sells an eight-view 1080p autostereoscopic 3D display designed for use in architectural design, industrial computer-aided design and molecular modeling. New York-based Magnetic 3D specializes in large autostereoscopic 3D displays for “3D digital signage” applications, such as presentations and educational displays. A Chinese company, TCL, has had a 42-inch autostereoscopic 3D television on the market since 2010 at a price of around US$20,000. It uses eight lenses on the screen to deliver a different 3D image to viewers, depending on their angle to the screen. Korea’s Samsung has demonstrated a prototype 50-inch autostereoscopic 3D screen that uses a similar “lenticular” system, but it has not announced a commercial product. China’s LG demonstrated a prototype 50-inch autostereoscopic 3D television in mid 2011, and recently launched a notebook computer with a 15.6 inch autostereoscopic display.
A new approach to autostereoscopic 3D developed by researchers at MIT’s Media Lab suggests a way that the quality and viewing range of 3D images could be improved even further. The MIT system, called HR3D, creates an optimal parallax barrier for every frame of video, instead of the simple narrow lines usually used to mask the left- and right-eye images. The result is a 3D image with a much wider viewing angle, and which keeps its 3D effect even when the screen is rotated. Although the HR3D method is computationally intensive – and so would drain a lot of battery power from mobile devices – the researchers hope it can be refined and handled by special-purpose graphics chips.
Although long a staple of science fiction movies, true three-dimensional video remains – unfortunately – as distant as jetpacks and flying cars. But experimenters are making progress. In 2010, scientists at the University of Arizona demonstrated a true 3D video system they called “holographic telepresence”, that allowed them to record a holographic image in one place and display it at a remote location, in real time, anywhere in the world.
The system uses a recently developed “photographic” polymer as a screen to show a true holographic 3D moving image, although only at very low resolutions and in monochrome so far. The moving image is recorded by multiple cameras to give multiple points of view, and the data can be streamed over the internet to the holographic display. The polymer in the display ‘captures” a copy of a laser-generated 3D hologram created from the video data that can be viewed from any angle, even from behind the translucent screen.
The prototype display is only 10 inches across, and it refreshes every two seconds, giving a very jerky video picture. But the researchers are confident they will soon be able to improve the size, quality, color and resolution of the image. Eventually it may be possible to develop a full-color system large enough to capture the human body and fast enough to give smooth movements – although the lead researcher, Professor Nasser Peyghambarian, warns it will be “at least seven to 10 years’ work” before a consumer version is available. Professor Peyghambarian sees applications for his technology in teleconferencing and in telemedicine, where surgeons at different locations around the world could use live 3D displays to observe and take part in remote surgical operations.
In early 2012, Microsoft Research demonstrated an experimental 3D imaging system called Vermeer, which is able to create a true 3D image in the space above a desktop. The Vermeer system does not use holograms but creates an illusion using opposing parabolic mirrors below the darkened transparent surface of the desk – an effect familiar from the toy known as a “Mirascope”. The desk includes cameras and sensors to detect when a user interacts with the illusory 3D object, giving the effect of a real 3D image that a user can touch and which can be viewed from any angle.