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When Apple first launched its “Retina display”, they chose the term “retina” not because these higher screen resolution displays would sit close to the eye. Rather, it was because it was supposed to be so good that the eye couldn't distinguish the individual dots. That was at the distance people held their smart phones - about one foot.
Retina gave users a resolution of about 300 ppi (pixels per inch). Indeed for computers (laptops, desktops and tablets) a lower pixel density also worked. Viewers couldn't see individual pixels on Retina displays. However when it came to VR displays, that resolution fell short. Even at 300 ppi, virtual reality headsets suffered from the so-called “screen door effect.” This meant that it was as if you were standing in front of a mesh screen door.
However, this is about to change in a week’s time at the SID’s Display Week in Los Angeles, on May 22. That's because displays of 1000 ppi and even 2000 ppi will appear there. This is something of a quantum leap over what is currently available. (Back in June 2017, we reported that Samsung was working on a GearVR model with 2000 dpi density. Currently we have no further information on that effort into higher screen resolution.)
However, it is worth remembering that the Apple first introduced the Retina display for the iPhone 4 in 2010. Older readers may remember that 25 years earlier, Apple introduced 300 dots per inch resolution for their LaserWriter printer. Ironically, printers have evolved beyond that. Printer density went up to 600 dpi and then to 1200 dpi. And this despite the fact that we don’t hold printed pages any close to our eyes than we used to.
Higher screen resolution: increasing pixel density
Unfortunately, similar improvements in pixel density for video displays have been stubbornly evasive. But this is a problem. The smartphone brought the screen closer to our eyes and the VR and AR display close still. So we can now look at printed images without seeing the dots, but we aren't so lucky with the pictures on our screens.
Now obviously some progress has been made in achieving higher screen resolution. Manufacturers have managed to push the 1080p screen format (1080 pixels height x 1920 width) into smaller screens. That's why we've got smartphones. Thus Apple introduced the 458 ppi “Super Retina display” on the iPhoneX. In effect, they maintained the existing resolution but improved brightness, sharpness and color fidelity.
However we still hold smartphones a comfortable 12 inches from our eyes. Not so for VR headsets. With head mounted displays, we have the screen an inch or so from our eyes. At that distance, the image must actually be focused on the eye. But even with the lens to focus the image, 400 ppi so close to your eyes creates a screen door effect. This the motivating factor behind the push for higher screen resolution.
Virtual Reality is driving higher screen resolution
The latest HTC Vive Pro, has improved resolution by 50%, achieving a pixel density of 615 ppi. But even this doesn't completely eliminate the screen door effect. Moreover, the Field of View of the Vive Pro is still only 110°. This still falls significantly short of the holy grail of Virtual Reality: filling the user’s central and peripheral vision with an FoV of 200° or 210°. To achieve that sort of FoV, and eliminate the screen door effect, will take lots of work. Aside from the screen display technology itself, it’s going to be pretty demanding on processing power. This is especially true given that VR gamers have grown accustomed to a 90 Hz refresh rate!
With VR it is not just about proximity. The lens doesn't just focus the image, it magnifies the dots. And this causes the user to see those dots. But the stronger the lens, the greater the distortion. If we can increase lens strength without loss of sharpness, then the screen can be made smaller. This will make it possible to build smaller VR headsets.Then we can get rid of the oversized monstrosities we have at present.
In an effort to develop higher screen resolution, Sony have teamed up with Toshiba and Hitachi on a venture called Japan Display (JDI). Last year JDI was working to achieve a pixel density of 803 ppi. However, they decided that even this was not enough and so they set their sights on 1001 ppi. And they achieved it. These advances, were aided by advances in lens technology, to focus the image over shorter distances, enabling the headset to shrink.
Higher screen resolution means Crossing the 1000 ppi barrier
JDI has also reduced the response time from 4.5 milliseconds to 2.2 and increased the refresh rate to 120 Hz. In effect, JDI has decided to bypass its own 803 ppi breakthrough and go straight to 1001 ppi. But while they will be showcasing the technology next week, commercial products with this resolution will not be available until March 2019. However JDI promises that even more advanced products will follow rapidly.
However, the Sony-Toshiba-Hitachi alliance isn’t the only player in the running. INT, a Taiwanese company claims to have developed 2228 ppi displays for Virtual Reality, under a team headed by David Chu, using “ultra high pixel density” AMOLED technology. However, whilst Chu’s team have announced the pixel density, they haven’t revealed the overall resolution, colour contrast, brightness, refresh rate or FoV. One thing is for sure: such resolution will not only reduce screen door effect, it will also alleviate vergence-accommodation conflict (VAC).
Meanwhile a partnership between LG and Alphabet (Google’s parent) has developed a 4.3 inch OLED display, built around 18 megapixels, with a density of 1443 ppi. That’s more than JDI, but less than INT.
We need processing power to match the graphics
In a week’s time, these displays will be unveiled to the public for the first time. All such technologies offer the prospect of sharper images and higher, more all-encompassing, FoV.
However, such resolutions - especially at the high refresh rate and low-latency required by VR gamers - will make heavy demands on computing power. Even high-end desktops struggle to deliver consistent and good performance at present-day, VR resolution, latency and refresh specs. And the trend - or at least the aspiration - is that VR will be liberated from the constraints of physical connectivity or even wireless connectivity to an external box. To bring these graphics advances to fruition on VR platforms, will require similar progress in graphics processing technology.
And it remains to be be seen how quickly that can be accomplished.