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                              A way of producing 3D TV images that work no matter where you are in the room could see images stand out from a flat TV screen – without the need for any additional glasses.Depth perception depends on differences between what our two eyes see, an effect called parallax. 3D movies simulate that effect by projecting the two views simultaneously onto the same screen. Viewers need special glasses that block one view from each eye at high speeds.The trick can work without glasses, too, as long as the screen includes structures called "parallax barriers", which deliver a different view to each eye. Nintendo's 3DS handheld games console, for example, uses this technology.
                        But the effect is quite crude and viewers must sit in a specific spot for it to work – fine for an individual holding a small screen, but no good for groups. Some, large glasses-free 3D screens are slowly becoming available on the market, but they also require the viewer to sit in certain "sweet spots".Ramesh Raskar and colleagues at the Massachusetts Institute of Technology (MIT) Media have developed "Tensor" – compressive displays that can create a wide field of view by splitting a 3D image into 2D slices for processing, in a similar way to a CAT scan.Slicing up picturesFirst, an algorithm works out which two slices of the image the viewer needs to see from any angle in the room to view a complete 3D image.
                      Light is sent through an array of small lenses, which refract it over a viewing angle that is about 50 degrees wide and 20 degrees high, and through an LCD screen that carries part of the final image. The light then passes through two additional LCD screens, which also contain elements of the final image, and in which the pixels switch between transparent or opaque at 120 frames per second, producing patterns that channel the correct 2D image slices to your eyes.Move your head to one side or the other, and two new slices of the original image come into view. Each eye sees a different 2D view of the image, and the brain combines them to form a clearer 3D image. The brain also combines features from a series of blurry, flickering individual frames to make sense of the image."It shows you strange-looking frames at very high rates," says team member Gordon Wetzstein. The individual frames flicker and contain noise and artefacts as the pixels switch on or off, but the eye responds too slowly to see the flaws in individual frames, and the brain simply blends the sequence of frames together."
                         The display deliberately exploits limits of the human visual system," says Wetzstein, who will demonstrate the system at the SIGGRAPH conference in Los Angeles in August. The project is still in its early stages and using displays with faster frame rates could increase both the viewing angle and the apparent depth of the display, he says."It is a great project, and a lovely piece of science, but I really can't see it being the 3D TV of the future," says Nick Holliman of the Visualisation Laboratory at Durham University, UK, who thinks the algorithm required to run the patterns will be too computationally intensive to be practical. He suggests that it might be best used for multiviewer advertising displays in airports and shopping centres.Counteracting cataractsFuture displays may soon go even further. 
                           Researchers from the Institute of Informatics at the Federal University of Rio Grande do Sul (UFRGS) in Brazil, Purdue University in West Lafayette, Indiana, and MIT have designed a screen that can compensate for bad eyesight, too."It creates hologram-style imagery that adjusts itself to the subject's eye conditions," says Vitor Pamplona of the UFRGS, who designed the prototype and will also present his idea at SIGGRAPH.We are experiencing a revolution in the field of displays, says Diego Gutierrez of the Graphics and Imaging Lab at the University of Saragossa in Spain. One day, he says, displays that can be tailored to an individual's visual impairments, could be incorporated into 3D displays.Pamplona's prototype consists of a small, high-resolution version of a parallax barrier created using two LCD screens on top of one another. "The higher resolution allows us to rebuild the image, pixel by pixel, and project it directly onto the eye of the viewer," says Pamplona.
                       The user types in their eye prescription and the system adjusts the apparent 3D depth of the image to bring it into focus. The algorithm can even take into account more serious eye problems, such as cataracts, by splitting the image into segments and placing the segments at focal depths that avoid the damaged part of the eye. But because it uses a standard parallax barrier, the system can only cater for one person at a time.Syndicated content: Jeff Hecht, Vijaysree Venkatraman, New Scientist

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