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Choosing the Right 3D Technology

Get ready. There's about to be a rush on video systems that display movies, images, and graphical information in three dimensions. Knowing the differences among 3D technologies is a key first step.



Because there's a slight separation between human eyes, each eye sees the same object slightly differently. The difference, known as parallax, is processed by the brain to create depth.

Stereoscopic 3D works the same way. Two slightly different images are projected onto a screen and the 3D system synchronizes the images so the viewer's left eye sees only images meant for the left eye and the right eye sees only images for the right eye. The resultant effect is interpreted by the brain as 3D.



• Passive 3D utilizes two projectors to display left- and right-eye information. Polarization filters go in front of each lens and left- and right-eye images are projected onto a screen specially designed to preserve the polarization. Viewers wear low-cost (often disposable) passive glasses.

• Active 3D includes a single projector, typically operating at twice the refresh rate (120 Hz) of dual-projector passive systems. Viewers must wear glasses that "actively" switch open and shut at the same rate to alternate left- and right-eye views.

• Active/passive 3D uses a single projector with a fast-switching, polarizing shutter in front of the lens. The system alternates left- and right-eye images at 120 Hz, while the shutter switches polarization in sync. Viewers use the cheaper passive glasses, but a polarization-preserving projection screen is also required.



The holy grail of 3D would be a solution that doesn't require glasses at all. Autostereoscopic displays are a significant step in that direction (autostereoscopic projection currently is in its infancy). With autostereoscopy, two channels of content are interlaced using a special screen barrier.

Autostereoscopic displays, for the most part, employ one of two technologies to produce the illusion of depth on a 2D flat display:

• Parallax barrier, in which a special layer of material is placed over a regular LCD screen, enabling each eye to see a different set of pixels. With parallax barrier technology, the viewer must sit in a specific location to achieve the effect. By nature, it can also block light output.

• Lenticular lens technology blocks less light and image resolution than parallax barrier. It uses an array of magnifying lenses that, when viewed from the correct angles, allow each eye to receive a different view of the same image, giving it depth. In general, lenticular technology supports more viewing angles. (For more about autostereoscopic 3D, read an interview with the CEO of Magnetic 3D at



Passive 3D may be the best option for large audiences because passive 3D glasses are generally less expensive than active glasses. Each projector in the system needs only to project at a standard refresh rate, so the system doesn't require extra bandwidth and standard cables and signal distribution can be employed.

Active 3D may be the best option for specialized or mission-critical systems. It could end up costing less over time because it uses a single projector, which should reduce the number of replacement lamps and the cost of ongoing alignment.

Active/passive 3D may be the best option when you want the best of both worlds: a high-quality 3D experience without the cost of active 3D glasses.

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