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.
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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.
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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.
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Source: Road to VR