dclark
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jhapeman wrote:
It's buried in an odd article, one on gaming monitors. In their FAQ on monitors for photography they only say you should use a monitor with a minimum of 100ppi and that more is better, but they don't put a ceiling on it. Of course they are happy to have you buy a 27" or 32" 4K monitor, like their two specialized for photography, which have 163 ppi and 137 ppi respectively. If it were easier/more economical to make 8K 32 monitors you can bet they'd be selling one and telling you of its virtues. 
https://www.benq.com/en-us/knowledge-center/knowledge/why-32-inch-4k-monitor-is-your-best-choice-for-console-gaming.html
Look, if you're getting old and have presbyopia I can get thinking it's wasted but honestly if that's the case you should also be wearing glasses to help you assess sharpness, so it's a bit of a moot point IMO. I get it that some people might not like a high-ppi screen, but there is no mathematical factual reason to not have a screen that has a ppi close to the resolving power of our eyes, and that means 5K at 27", 6K at 32". Even 4K at 27" is 163 ppi, much higher than the 100 ppi people are advocating on this thread, and yet you'd be very hard-pressed to find any 27" monitor today that isn't 4K, particularly one targeted at photographers and graphics professionals. ...Show more →
Thanks for the URL.
Anyone with some experience in image science will quickly conclude something is wrong when they see the BenQ table you posted. That’s why I asked for the URL so I could see what they had done.
A quick summary is that the table is off by a factor of 2, and consequently your comments about monitor PPI are also off by a factor of 2.
The table BenQ provides is easily reduced to a simple formula, "Max PPI" = 572 / (viewing distance in feet). That is of course the kind of formula that would describe the visual acuity of the human eye-brain system.
The BenQ table you are using seems to be almost exactly 2X the formula for 20/20 visual acuity (see Wikipedia). What I get from the definition of 20/20 vision is "Average visual acuity PPI" = 286/(viewing distance in feet). This is nothing new. Measurements of human visual acuity have been made and documented in the scientific literature for many years, and are the basis for the long standing conclusion that display pixel densities above 100-140 PPI have greatly diminished value for display of continuous tone images. Human visual acuity is not changing anytime soon, regardless of advances in display technology.
I checked to see how BenQ produced their figures and found that they use that the eye can resolve about 60 lines per degree of view. That is correct if by 60 lines you mean 30 black lines and 30 white lines (i.e. 60 alternating bands). The more unambiguous correct statement is that the eye can resolve high contrast bands that are separated by ~1 arc-minute. That is essentially identical to the definition of 20/20 vision acuity which is at a distance of 20 feet the average eye can resolve high contrast bands that are 1.75mm apart. BenQ seems to have taken 60 lines per degree to mean 60 black and 60 white lines. Regardless, they got it wrong by a factor of 2x.
It is also well known that visual acuity is better for vector graphics than continuous tone photos. That’s why you will notice pixelation in fonts at higher pixel densities than you will notice pixelation in photos, and why high PPI displays show noticeable improvements in text and other graphics even though any improvement in photos is harder to see. That means visual acuity is a bit worse than 286/distance(ft) for contone photographic images.
The result of using the incorrect table is that your comments on the monitor pixel density that the average eye can resolve need to be revised downward by a factor of 2.
For example the statement "What the facts and numbers do show is that if you have average or better visual acuity there is absolutely no wasted resolution even up to almost 300ppi, with a clear sweet spot around 200ppi" needs to be revised to "What the facts and numbers do show is that if you have average or better visual acuity there is absolutely no wasted resolution even up to almost 150ppi, with a clear sweet spot around 100ppi".
It’s interesting to note that in the BenQ article, just above the posted table, they say “Considering these limitations and the human eye's resolving power, a good range for monitors is 100 to 150 PPI.“ That’s the correct conclusion but their adjacent table says that would mean sitting 3.8-5.7 feet from the display! They seem to know enough about the science to know the right conclusion, even though it has an obvious conflict with their table. I don’t know why that did not trigger them to check their table and correct it. The inconsistency should also trigger readers to be cautious about the reliability of the information.
It’s true that the 2X higher pixel densities can be useful if the viewer moves 2X closer. The usual viewing distance for monitors is around 20-24”. If the viewer temporarily moves closer to 10-12” the ability to resolve pixels doubles and image can be quickly assessed. It’s also true that some people have above average visual acuity (about half are above average, about 80% think they are above average). A very few have 20/10 vision so the table would be correct for them.
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