3D Televisions – How Do They Work?

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Home 3D televisions work in one of the two ways. They can either use active shutter glasses and high refresh rates to deliver images to one eye at a time or they can use autosterescopic displays. These differ from the 3D movies we see in theaters which use passive 3D technology with polarized glasses. The active shutter glasses are not polarized and the autosteroscopic displays don’t need glasses at all.
Movie 3D delivers a doubled image that is either filtered by color or by polarization. The glasses are passive in the way they work. This is called anaglyphic 3D viewing or polarization 3D viewing. The display works because the image is filtered by the glasses into the viewer’s left and right eye although both are displayed all the time.
3D televisions that use shutter glasses have active lenses that flicker in time with the refresh rate so that each eye only sees the frames that are meant for it to see. This is called alternate frame sequencing, or active 3D. Typically these televisions have a 120 frame per second refresh rate that allows it to show 60 frames for each eye per second. The glasses they come with uses a filter that flicks off and on in sync with the television to deliver the proper image to each eye. Most of the 3D televisions on the market today use this type of technology.
Of course, ideal home 3D would ditch the glasses, because watching a movie should be a group experience. Currently there are a couple of companies who make 3D screens that are viewable without glasses. These televisions use optical elements as part of the screen to create the 3D illusion. They are flat panel televisions that use lenticular lenses or parallax barriers to deliver different images to each eye.
The drawback to these technologies is that they are designed to create a good 3D image only at a specific distance and across a narrow range of angle. The lenticular lens system used by LG, for example, requires an optimum viewing distance of exactly thirteen feet. Parallax barriers, like those used by Sharp’s 3D televisions, can be either hard lenses or liquid crystal formed ones. The liquid crystal style has the advantage of being able to be switched off to allow traditional TV viewing on the same set.
In more recent years there have been alternative types of these screens come out, like Integral Imaging that uses micro images which are viewed through an array of spherical convex lenses which the brain then sees as a 3D image. This is a hard lens form of the parallax barrier. HoloVizio has come up with a form of parallax called “continuous motion” that uses “voxels.” These are replacements for pixels that project several beams of light in several directions at the same time.
Should these glasses-free forms of 3D televisions become popular, people would have to design rooms that were long and narrow to allow for optimal viewing by the most people. In the mean time, the active 3D technology continues to drop in price, allowing more people to afford these types of setups, which work with 3D Blu-ray disc players and 3D streaming media.

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