If there is any single number that people point to for resolution, it is the 1 arcminute value that Apple uses to indicate a “Retina Display”.
Earlier in my job where I work, I had to try and recommend the resolution people needed to get a good picture using a scanner or a digital camera. As we know the resolution arms race knows no bounds. First in scanners then in digital cameras. The same is true now for displays. How fine is fine enough. Is it noticeable, is it beneficial? The technical limits that enforce lower resolution usually are tied to costs. For the consumer level product cost has to fit into a narrow range, and the perceived benefit of “higher quality” or sharpness are rarely enough to get someone to spend more. But as phones can be upgraded for free and printers and scanners are now commodity items, you just keep slowly migrating up to the next model for little to no entry threshold cost. And everything is just ‘better’, all higher rez, and therefore by association higher quality, sharper, etc.
I used to quote or try to pin down a rule of thumb I found once regarding the acuity of the human eye. Some of this was just gained by noticing things when I started out using Photoshop and trying to print to Imagesetters and Laser Printers. At some point in the past someone decided 300 dpi is what a laser printer needed in order to reproduce text on letter size paper. As for displays, I bumped into a quote from an IBM study on visual acuity that indicated the human eye can discern display pixels in the 225 ppi range. I tried many times to find the actual publication where that appears so I could site it. But no luck, I only found it as a footnote on a webpage from another manufacturer. Now in this article we get more stats on human vision, much more extensive than that vague footnote all those years ago.
What can one conclude from all the data in this article? Just the same thing, that resolution arms races are still being waged by manufacturers. This time however it’s in mobile phones, not printers, not scanners, not digital cameras. Those battles were fought and now there’s damned little product differentiation. Mobile phones will fall into that pattern and people will be less and less Apple fanbois or Samsung fanbois. We’ll all just upgrade to a newer version of whatever phone is cheap and expect to always have the increased spec hardware, and higher resolution, better quality, all that jazz. It is one more case where everything old is new again. My suspicion is we’ll see this happen when a true VR goggle hits the market with real competitors attempting to gain advantage with technical superiority or more research and development. Bring on the the VR Wars I say.