Donning a pair of virtual reality goggles like the Oculus Rift can instantly transport you into another place. But being able to see the pixels that make up that computerized world can be a niggling reminder that your brain is being tricked by an LCD panel strapped to your face.
Researchers at Nvidia now have a possible solution. They have built a prototype VR headset to demonstrate a technique that can quadruple the pixel density of an LCD panel. They call their new design—made by modifying two off-the-shelf LCD panels—a “cascaded display.”
“This is useful in applications like a head-mounted display, where each pixel looks really large because it is very close to your eye,” says David Luebke, a senior director of graphics research at Nvidia.
Although competition among smartphone manufacturers has led to significant increases in the pixel density of commercial LCD panels in recent years, the displays on the market today don’t pack pixels densely enough for them to be invisible at very close range.
The Nvidia design exploits the fact that LCD panels use an array of tiny shutters that control the visibility of individual pixels. The researchers extracted the array of shutters from one LCD panel, and then placed them over those in another panel of the same design. The extra layer is positioned so that its pixels are just slightly offset from those of the panel below. The boundaries of the extra shutter layer divide up each pixel of the panel below into four smaller areas—these are the pixels of the new, cascaded display.
This design reduces the brightness of the display, because light has to pass through more components to reach the viewer. But this isn’t critical for a VR headset, where the display is close to the eye in a dark space.
Making use of that extra density requires some mathematical tricks, because when a shutter in the upper array changes its brightness, that affects four of the pixels visible to a person looking at the display. The Nvidia researchers have developed software that can translate the feed from a video or game into instructions for each layer to create the desired image for a viewer.
Cascaded displays can also offer an increased frame rate, which means moving images appear smoother. Setting the panels to refresh out of sync with one another causes someone using the display to see new frames at twice the rate each individual panel is updating.
Pixel density is far from the only factor that affects the quality of virtual reality experiences. Doug Bowman, a professor at Virginia Tech, says that his research suggests that having a wider field of view has perhaps the strongest effect on how immersed people feel in a virtual space, and how well they perform at tasks inside it.
One reason the Rift has been so well received is that it offers a wide field of view compared to previous headsets, at a relatively low cost. However, even the Rift’s 100-degree field of view imposes a kind of tunnel vision on people wearing it, because the human visual field is close to 180 degrees. Displays with greater pixel density could make it possible to cram more pixels into a headset so that when spread across a wide field of view by lenses—as in the design of Oculus Rift—they remain relatively densely packed.