There are currently two key methods for delivering 3-D content to the home. Most 3-D sets being sold today rely on the method called “frame-sequential display.” Part of the main 3-D Blu-ray specification, this delivery method consists of a sequence of alternating frames meant for each eye.
Frame sequential lends itself to the active-shutter-based technology used for today’s 3-D TVs. The active-shutter glasses used for viewing must sync with the 3-D TV set to allow the correct eye to view the correct image at the precise time. The active-shutter glasses turn opaque and switch the eyepiece so the viewer can process the correct image at the moment it is intended.
For broadcasters, however, sequential viewing uses too much bandwidth. It is essentially displaying two images — one for each eye. Efforts were made to reduce the bandwidth used for 3-D delivery to be about the same as that used for HDTV.
3-D TV sets are actually computers that can process a variety of formats and perform on-the-fly conversions. Seeking to lower the needed bandwidth for 3-D delivery, broadcasters devised side-by-side technology as an alternative way to deliver 3-D to the home.
When it launches this month, DirecTV will be airing 3-D programming by using the side-by-side 3-D format. ESPN also will be airing 3-D content using a 720p, 60fps side-by-side format for its World Cup coverage.
Side by side uses the same bandwidth as standard HD transmissions and only half that of frame-sequential technology. Using 24fps, it splits the image into two frames — one for each eye. It doubles the length of each segment, and then displays those images sequentially for the shutter glasses.
While not as dense or rich as frame-sequential images, it uses far less bandwidth and requires no new set-top box hardware. Pay-TV providers need only provide a simple firmware update to their equipment.
ESPN has done some testing with 720p side-by-side content for sporting events, and the feedback from initial testers has been positive.