Today’s VR headsets may have relatively high resolutions on paper, but when the pixels are stretched across a wide field of view, the effective angular resolution is far lower than what you might expect from a typical 1080p TV or monitor. Unfortunately, a suitable VR display capable of achieving both a wide field of view and retina resolution isn’t readily available yet. Until then, Finland-based VR startup Varjo is using a combination of macrodisplays and microdisplays to put high density resolution to the center of your view without giving up the wide field of view.
The Varjo headset makes use of what the company calls a ‘context display’ and ‘focus display’. The context display is a large macrodisplay with a 1,080 × 1,200 resolution spread across a 100 degree field of view. Alone, it would look almost identical to the fidelity you’d expect from the Oculus Rift or HTC Vive. Varjo’s trick however is putting a microdisplay (the ‘focus display’) with a 1,920 × 1,080 resolution at the center of the headset’s field of view. Although the focus display isn’t tremendously higher resolution than the context display by pixel count, it’s pixels are packed into just 35 degrees horizontally, making it incredibly pixel dense.
Photo by Road to VR
At MWC 2018 I got to check out the Varjo Alpha prototype headset. Inside I saw an extremely high quality image at the center of my field of view which had no noticeable screen door effect. Beyond that 35 degree rectangular area, the resolution drops to the same levels you’d expect from first-gen consumer VR headsets. At the boundary between the focus display and context display, there’s an imperfect transition between the high resolution area and the low resolution area, which looks like a blurry rectangular halo, but it was actually somewhat less jarring than I was expecting.
A rough approximation of how the focus display looks against the context display. Relative fields of view are not to scale. | Photo by Road to VR, based on images courtesy Varjo
The company is using an optical combiner, essentially a two-way mirror, to composite the two displays. Going forward, Varjo hopes to further smooth out the transition between the two displays, the company’s CMO, Jussi Mäkinen, told me, using a combination of both hardware and software refinements.
The difference in quality between the focus display and the context display is truly night and day. Not only does the focus display not show any noticeable screen door effect, the jump in angular resolution turns otherwise blurry smears into perfectly legible letters, as a virtual standard eye chart placed inside the demo experience made clear. Textures benefited immensely from the improved angular resolution, revealing detail that simply isn’t visible on the lower resolution context display.
In the video above, keep your eye on the lower lines of the eye chart to get an idea of the difference in resolution between the focus display and the context display. The resolution jump is less noticeable here since the camera isn’t capturing the headset’s full field of view. You can’t quite see the boundary artifacts in this video.
The Vajor Alpha prototype was tracked with SteamVR Tracking, which the company plans to continue using going forward. Since this was a handheld demo (no strap on the headset yet), I didn’t do a comprehensive test of the headtracking tracking in its prototype form.
In its current state, even with a static focus display, the benefit of the extra resolution is apparent, and you can almost fool yourself into thinking the entire display is sharp, as long as you consciously try to keep your gaze pointed through the very center of the lens. Of course, course, in practice, your eyes are not always looking perfectly through the center of the lenses, so you won’t always be looking at that super sweet spot of the focus display. And you’ll have to contend with your eye crossing back and forth over the transition point (and back and forth between high res and low res).
Varjo’s long term hope is that they’ll be able to move the focus display in real-time, creating a sort of hardware foveated display, such that the focus display is always at the center of your gaze no matter where you’re looking. That would of course require excellent eye-tracking (and then some) but if they can pull it off, it would make the headset even more compelling because your eye would never have to cross the border between the displays (and always be in that super sweet spot), and your brain might even do a good job of ignoring the border if it’s always a fixed distance from the center of your view.
Achieving an active focus display isn’t likely to be an easy task, though Varjo has patented several potential approaches, mostly involving quickly pivoting the optical combiner about two axes, which we examined recently when we explored the company’s key technology.
Though Varjo CMO Jussi Mäkinen tells me that the company already has prototypes with an active focus display, it’s still up in the air whether or not Varjo’s first commercial product, which is planned for release later this year, will use a static or active focus display.
Photo by Road to VR
Mäkinen told me that Varjo is for now focusing exclusively on enterprise and commercial applications for the headset, which the company initially expects to price between $5,000 and $10,000. He said that the company is actively listening to feedback from its partners about what aspects of the headset are most critical for improvement.
If Varjo can develop an effective and reliable mechanism for active foveation, their headset could be great stopgap for making near retina quality VR headsets with a wide field of view before any single display (per-eye) is ready to ready to deliver such an experience. But we know that both macrodisplay and microdisplay makers are working toward that goal, so where does that leave Varjo once a single display can do it all?
Mäkinen says that Varjo doesn’t just want to make a headset, they want to pioneer the productivity use-case of VR, using a mix of hardware and software. One example he gave was using a totally virtual workspace without the need for physical monitors, something that can really only happen once headset resolution is high enough. He said we can expect more from the company on the software side in the future.