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Transmitting 3D in a 2D World

Producing 3D high-definition pictures requires new camera systems that incorporate two lenses—to generate separate images for the left and right eye—and displaying them in the living room means buying a new HDTV set that comes with special glasses to assemble the 3D images. But delivering 3D HD TV to the home may not necessitate the complete overhaul of the program transmission chain that early 3D skeptics had forecast.

That's because networks and pay-TV operators launching 3D HD in 2010 plan to transmit their video in “frame-compatible” broadcast formats that are designed to work within the existing bandwidth for HD transmission. Such formats use spatial compression to reduce the horizontal or vertical resolution of the left- and righteye images. That is a compromise early 3D programmers can live with, as adopting “full 3D”—delivering full resolution to each eye—would require doubling the current bandwidth used to deliver twodimensional HD to the home.

More important, frame-compatible 3D formats, which can squeeze the leftand right-eye images into a normal HD program stream by interleaving them in a side-by-side or top-bottom configuration, among others, are also supported by some existing high-end satellite and cable set-tops. Such broadcast 3D formats are expected to be incorporated into the latest version, 1.4a, of the High-Definition Multimedia Interface (HDMI) networking technology that is commonly used to provide a secure digital connection between digital TV sets and set-top boxes. Existing late-model set-tops with an HDMI Version 1.3 connector can receive a software update that will allow them to connect to new 3D sets with a Version 1.4 connector to display 3D HD video.

DirecTV, which plans to launch several 3D channels in June, met with Japanese and Korean set-makers last fall to brief them on its 3D transmission plans and ensure that its existing MPEG-4 HD set-tops would work with new 3D TVs. The pay-TV operator demonstrated live 3D HD satellite broadcasts using frame-compatible 3D, in the side-by-side interleaved format, at the Consumer Electronics Show in Las Vegas last month. British pay-TV operator Sky employed a similar technique to deliver a live 3D soccer broadcast to a handful of pubs in the U.K. and Ireland two weeks ago. And cable sports giant ESPN says it will use spatial compression to deliver its new 3D network, which plans to go live with the 2010 FIFA World Cup in June.

Executives from encoder manufacturers Harmonic, Ericsson, Motorola and Harris say their products can support frame-compatible 3D, with at most a software upgrade required to optimize the processing of 3D images. “Our encoder has been used by at least three major customers, and it works just fine delivering 3D images all the way through,” says Matthew Goldman, VP of technology for Ericsson’s TV solutions business (formerly known as Tandberg Television).

Ericsson’s latest contribution encoder can also support the backhauling of live 3D images from the field, Goldman adds. A single CE-xH42 unit can receive left- and-right eye camera feeds, encode them separately, and send them back to a network in a single “phase-aligned” stream that ensures the left- and right-eye images stay in sync when decoded.

DirecTV, which uses a mix of Harmonic and Ericsson MPEG- 4 encoders to deliver its HD programming, won’t need any new hardware to transmit 3D in the 720p, 1080i or 1080p/24 frame-persecond formats, according to CTO Romulo Pontual. But the company, which showed 1080p/24 3D at CES, has licensed technology from 3D display specialist RealD and is working with encoder vendors to optimize their software.

“It’s some of the preprocessing [capabilities] they don’t have,” Pontual says. “Part of that is done at the program producer, and part of it is done at DirecTV.”

Pontual says DirecTV will likely use a slightly higher bitrate for 3D than it currently uses for its normal MPEG-4 HD streams, but he wouldn’t give a specifi c number. He did dismiss the notion that fitting 3D in the same bitrate as 2D HD, by using the side-by-side interleaved format, means cutting the horizontal resolution in half.

“That’s absolutely not true,” he says. “It would only be half if you were transmitting identical left- and right-eye images. 3D already gives me a gain, as every odd pixel to one eye is representing an even pixel to the other one. If you’re smart in how you’re picking pixels, you can get a very high horizontal resolution.”

The technology behind frame-compatible 3D isn’t exactly new. Montreal-based Sensio Technologies has been specializing in spatial compression techniques for 3D video for a decade, and unveiled its first product for high-end home theater systems in 2003. It now sells its proprietary decoding technology in its own 3D chips and also licenses it to other manufacturers. The company announced at CES deals to license its 3D video processing technology to set-makers Vizio and ViewSonic and home-theater technology provider THX, and it has worked with ESPN and the NBA on early 3D tests.

Sensio’s implementation of spatial compression technology creates a “virtually lossless” end picture for the viewer, says Richard LaBerge, the company’s executive VP and chief marketing officer, even though either horizontal or vertical resolution must be sacrificed to deliver 3D down an existing 2D pipe. As LaBerge puts it: “There’s a way to play with each pixel.”