In this era of ubiquitous smart phones, we are all familiar with the ‘resolution’ of a screen: a number, or often a pair of numbers, which tells us how many pixels there are on the screen. For example, the shorthand 1080p, means there are 1920 x 1080 = over 2 million pixels. A ‘4k’ screen has over 8 million pixels.
However, the resolution of a screen is not the be all and end all when considering a screen’s quality.
If you bring your mobile phone close to your face and squint, you may be able to see black lines separating the pixels that make up your screen. This is very difficult with the more expensive smart phones, as the pixels are so small and the pixel density is so high. Perhaps you’ll have more luck with your TV or computer monitor.
If you can’t spot the spaces between the pixels, instead imagine that your phone screen is enlarged to the size of a cinema screen. The black lines between the pixels would be much more visible, and it would look like the picture displayed by the pixels is being shone through a mesh. When this effect is visible, it is known as the ‘screen door’ effect. Obviously, this is not a problem with the current generation of smart phones
In many virtual reality headsets however, this effect is not just visible, it is pronounced and distracting (I can attest to this, as the owner of a popular VR headset). This is because the screens displaying the image are close enough to your face for the spaces between the pixels to be much more visible compared to, say, your phone; the lenses in the headset putting the image and the dark lines in clear focus. The result is that everything you see in your virtual reality headset appears to be overlain with the mesh of a screen door.
How are innovators addressing the screen-door effect in virtual reality headsets?
The obvious solution to this problem seems to be just to add more pixels, so that the pixels get closer together as a consequence. This brute-force type solution would work, but the more pixels there are, the more processing power is required to render the image for display. Higher resolution monitors also drive up cost, which is already a prohibitive barrier to entry for VR technology.
Samsung has designed an interesting device – a diffusing grid – and integrated it into its latest generation of HMD Odyssey+, a Windows Mixed Reality headset. The diffusing grid softens the light coming from each pixel. The softened light appears to close the apparent spaces between pixels such that rendering of additional visual data is not required. This eliminates the need for higher pixel density and additional processing power.
However, this softening effect arguably only circumvents the problems of the screen door effect, rather than solves them.
Sony’s Playstation VR headset, the PSVR, has an on-paper resolution lower than that of its contemporary, the Oculus Rift. However, the PSVR has far less of a screen door effect. This is because Sony spatially separated the pixels making up the PSVR monitor into their red, green, and blue sub-pixel components. This separation narrows the spaces between each RGB set of pixels. As a result, the spaces are less visible, at the cost of slightly reduced detail.
As innovation in VR technology continues, and monitor pixel density increases in newer generation headsets, the screen door effect will almost certainly begin to disappear. However, the significant effect on user enjoyment and immersion, demands that the screen door effect be directly addressed with clever, patentable solutions rather than overcome with brute force. I look forward to finding out more about how VR innovators are solving this particular problem.
