There is quite a bit of confusion when we talk (and hear) about resolution. Resolution is measured in pixel per inch, that is how many different points are in an inch. On a 4k television you have 3,840 points horizontally and 2,160 vertically. How many per inch? Well that depends on how big the screen is! If you have a 43″ screen (diagonal) you get a 102.4 ppi horizontally and 100,4 vertically, so let’s say we have 100 ppi resolution. But if you have a 60″ screen (diagonal again!) you get 73.4 ppi horizontally and vertically.
What you hear is that a 4k resolution matches the human eye resolution so that you no longer can single out the points on the screen, rather you see a continuous image. Actually, the eye resolution is measured in arc-seconds, precisely it is 28 arc-seconds that means 0.008 degree angular resolution. To use a more understandable measure it means that a perfect visual acuity (not mine!) would be able to single out two points at a distance of 6 meters that are separated 1.75mm one from the other. Hence, when people say that 4k screens are above the human eye resolution it means that viewing those screen from a reasonable distance (measured in meters) you won’t be able to see the tiny points making up the image.
Now, consider the new amazing screen of an iPhone 12: the smaller display model has a 2430 x 1080 pixel screen, hence a resolution of 476 ppi. As you see, the number of pixels is way less than a 4k screen but the resolution (ppi) is 5 to 7 times higher. Are we seeing a better image on the iPhone than on the television? Not at all! The reason is that we are looking at the iphone screen from a much shorter distance, hence the need for a higher number of ppi.
Suppose now to look at a display that is placed 1 cm away from your eye. In order to keep the same image quality you would need a much higher resolution, much higher ppi. With a back of the napkin calculation you get that you would need an equivalent resolution of 9,520 ppi (assuming a display 1/6″).
This is why you need really high resolution for VR devices, particularly if you aim at seamless ones. With bulky ones, like the one we have today, you can place the display a bit further away from the eye, hence you can have a bigger size and use a lower resolution. You would need, however, something in the 3,000 ppi to get an image that can fool your eye and this is why today VR goggles are providing images that feels like artefacts, not real world images.
Here comes the news of the result of a joint collaboration between Samsung and Stanford University. Researchers have created an OLED screen made of two reflective surfaces, one silver and the other (a meta-surface) consisting of nano pillars, 80 nm high and 100 nm wide, each serving as a pixel. Each pixel can be made to reflect a specific wavelength, a specific color, thus composing the image. The current prototype can reach a 10,000 ppi and further evolution may push the resolution to 20,000 ppi.
The light bounces off, back and forth in the two reflective surface before getting out from the silver film covering the panel surface resulting in a luminosity improvement of 2 times and delivering purer colours.
It took OLED some 10 years to move from the research llabs to our living room and it is most likely that a similar amount of time will be required before we can “wear” this technology. The timing, though, will be in synch with the increase of battery efficiency (particularly delivering a much shorter recharging time) and low power/high capacity processing that will be converging into a seamless access to the cyberspace (XR) shifting our life into the future “digital reality”.
If you are fascinated, as you should, by these evolutions consider joining our Digital Reality Initiative and attend the very first conference on Intelligent Reality scheduled for March 17-19, 2021 and whose call for paper is still open.