Television manufacturers and content producers started out the year pushing 3-D television hard, hoping to ride the wave of success enjoyed by the 3-D movie Avatar. Though glasses-free 3-D is still some ways away, manufacturers hope to entice consumers with a flurry of products that make the best of the difficulties with bringing 3-D content to the small screen.

Producing a 3-D television that doesn't require glasses is "impractical for the foreseeable future," says Peter Fannon, vice president of corporate and government affairs for Panasonic.

Demos featuring glasses-free 3-D television technology have yet to pan out into real products. Two years ago, Mitsubishi attracted attention by showing off glasses-free 3-D research technology, but the company has no products based on the work.

Fannon says that a key trouble with glasses-free 3-D is that it would significantly raise production costs. Most glasses-free TV displays use a lenticular lens, which gives off light at different angles--so that a different image reaches each eye. Such a display requires images of the same object to be captured from many different angles, forcing content producers to film and process the same scene from a dozen or more angles at a once. "That's a production cost no one can bear," he says. Lenticular lenses can also distort a picture, and viewers often have to watch from a specific angle.

Instead, 3-D technologies in use today employ glasses to control the images. The most common technology, used in movie theaters, is made by RealD, a company based in Beverly Hills, CA. This technology uses a special screen to reflect polarized light to the audience when images are projected onto it. The glasses then filter the light so that images are directed correctly to each eye.

RealD has made deals with many of the major manufacturers, including Sony, JVC, Samsung, Toshiba, Panasonic, and DirecTV, to use its format to deliver 3-D content to televisions. However, the majority of 3-D televisions use "active eyewear" to process 3-D content for each eye, unlike the passive glasses used in movie theaters.

Active glasses for 3-D are battery-operated, and they have lenses that rapidly shutter open and closed. The television display--often an LCD or plasma screen--works double-time, cramming in twice as many pictures so that a each eye sees a continuous, high-quality image.

A RealD spokesman explained that the special screen technology used in movie theaters, where the display does most of the work, would be too expensive if translated to 3-D TVs for consumers. Active glasses, on the other hand, are too expensive for movie theaters to hand out in volume, but work well for home users.

Panasonic's Fannon adds that polarized glasses work best in a dark environment, where a large screen fills the audience's entire field of vision. Active shutters are better suited to the home environment, he says.