Satellite, Cable 3D broadcasts won't be "Full HD"

When the specifications for 3D Blu-ray players were developed, one key element was the ability to offer 3D movies in "full HD resolution," which requires the player to send a TV two 1080p video streams, one for each eye. That was possible because the devices were new, and they would include new HDMI 1.4 connectors, which provided support for dual 1080p 3D streams.

But 3D broadcasts will also be part of the equation, and at least initially, they'll be sent over existing cable and satellite infrastructure, including current cable/satellite settop boxes, which the companies promise to upgrade. However, while these upgrades will enable some current cable and satellite boxes to live in the 3D world, they will have one drawback: at least initially, they won't support 3D in the same full 1080p resolution offered by new 3D Blu-ray players

That's because these new "frame-compatible" 3D broadcasts—where the separate left- and right-eye signals are combined and sent like a standard 2D HDTV video frame—require broadcasters to use spatial compression that reduces the image's resolution so that the left- and right-eye views can be squeezed into a single frame.

There are several ways to do this. DirecTV—which will be updating the firmware in its receivers in June to accommodate three new 3D channels, plus the ESPN 3D channel—will use a technique called "side-by-side" 3D, where the horizontal resolution—1080i/60Hz (1920 x 1080) of the image is compressed by half (960 x 1080) so two images can be placed next to each other within a single frame.

Other companies may use "top/bottom" 3D, where the vertical resolution—either 1080p/24Hz (1920 x 1080) or 720p/60Hz (1280 x 720)—is compressed by half to allow left- and right-eye images to be placed on top of each other in a single frame.

In both cases, the TV then takes these lower-resolution frames and expands them into a full-size image based on the TV's native resolution.

The big question, of course, is how these 3D broadcasts will look compared to what we're now seeing with 3D Blu-ray titles. Broadcasters are hoping the answer is "good enough," as it will be some time before they can transition to full 1080p 3D programs. In addition to DirecTV, several cable companies, including Cablevision, Comcast, and Cox, have also announced plans to offer some 3D broadcasts to subscribers. While these will undoubtedly be in lower resolution than the 3D images coming off a Blu-ray disc, some argue that loss of resolution won't be readily apparent given the screen size of most TVs. But others says movies on Blu-ray will look decidedly better than their broadcast counterparts.

Obviously, this is something we're looking forward to testing in our labs. Also, since I've been a DirecTV subscriber for several years, I've already warned the test-lab engineers that I'll be borrowing a new 3D TV for a few days when DirecTV launches its 3D programming to see for myself how the broadcasts fare. While this is certainly fertile fodder for a blog, I have to admit there's another agenda—I'm hoping that actually having a 3D TV in the house will soften my wife's staunch stance against getting a new 3D TV for the family. I'll let you know how that works out for me.

—James K. Willcox