Next-Gen 3D Sets Could Solve Passive/Resolution Tradeoff

The debate over passive vs. active 3D glasses, and their respective tradeoffs, may be history sooner rather than later, according to Matt Cowan, chief scientific officer of RealD. Next-generation developments, he says, promise to combine the best of both worlds.

During a presentation at the SMPTE 3D Conference in New York City last month, Cowan laid out new technical approaches that could allow passive glasses to be worn without compromising image quality.

Passive glasses, though lighter and more affordable, suffer from greater resolution loss (roughly 50%) compared with active glasses. With passive glasses, spatial multiplexing and a patterned retarder film over the set create polarized strips with opposite polarization so that the left eye sees the even lines and the right eye sees the odd lines. But the resolution is cut in half, and there can be crosstalk (or one set of lines leaking through to the other eye) if the viewer is above or below the ideal viewing axis.

“Those displays also play havoc with small text,” Cowan added, “because of diagonal lines of visible black strips between the active rows.”

Those limitations are one of the reasons that a newer alternative, with the patterned retarder film active and the polarization “actively” switched, may have an impact on the market in 2012 in HD sets at 120 and 240 Hz as well as in laptops.

“It offers full resolution,” said Cowan, and, without the insertion of a black frame, brightness levels are maintained. Also, with such technology as a segmented modulator in front of a scrolling backlight, areas of crosstalk could also be eliminated.

“With switching at the display, the shutter is just fully open or closed,” he says. “The signal doesn’t scan down.”

In the meantime, displays with active glasses offer the best alternative for those hungry for resolution.

“Active displays are dominant in the home today,” he said of the technology, which uses glasses with “active shutters” synched to the TV set via IR or Bluetooth signal. The synched signals activate liquid shutters in the glasses that then, alternately, allow light into the left and right eye.

“The limitations of active are battery life [because the glasses need batteries]; they are heavy, expensive, often incompatible with other sets; and the transmission is dark because, half the time, a black frame is inserted in between the frames, with the remaining frames being split between the left and right eye,” Cowan explained.

“But,” he added, “active glasses deliver a good visual performance, and universal glasses are beginning to become available that respond to every type of synchronization.”