Categories

# Notes by Dr. Optoglass: The Resolution of the Human Eye

Topics Covered:

• The average and maximum resolutions of the human eye
• PPI and DPI at various distances

Beauty is all very well at first sight; but who ever looks at it when it has been in the house three days? – George Bernard Shaw

Exclusive Bonus: Download my free cheatsheet (with examples) of the most important and useful focal lengths for film and video (PDF file optimized for mobiles and tablets).

As we have seen earlier, the average visual acuity of the human eye is one arc minute. The maximum possible is 0.4 arc minutes. It would be a very rare human indeed who can beat 0.4 arc minutes!

Therefore, we can safely say that the average resolution of a good eye is between 0.4 and 1 arc minute. Before these figures can be translated to pixels or displays, one needs to realize that the size of the pixel will vary with distance.

What’s the formula?

where

• d is the distance in mm
• ? is the angle in degrees

A very young child can focus at about 2 inches, but the average adult can focus no closer than 4 inches (100 mm). We can assume the lowest value of d to be 100 mm. At this distance, the pixel/dot size p is 0.0116 mm or 11.6 microns – for 0.4 arc minutes. For 1 arc minute, it works out to be 29 microns.

An inch is 25.4mm. So how many of our pixels can fit into an inch? @0.4 arc minutes, it is 2190 ppi (dpi). @1 arc minute, it is 876 ppi (dpi)

Maximum Resolution of the Eye

So this is how it is. If a healthy adult brings any display screen or printed paper or whatever 4 inches (100 mm) from his or her face, the maximum resolution he/she can see at is 2190 ppi/dpi. It doesn’t get any better than this for 99.99% of us, except maybe during pre-kindergarten years.

But the legally accepted norm of 20/20 vision only asks for 876 ppi/dpi at 4 inches!

Let’s have some fun:

Magazines and Fine Art Prints

If the average reading distance is 1 foot (12 inches = 305 mm), p @0.4 arc minute is 35.5 microns or about 720 ppi/dpi. p @1 arc minute is 89 microns or about 300 dpi/ppi. This is why magazines are printed at 300 dpi – it’s good enough for most people. Fine art printers aim for 720, and that’s the best it need be. Very few people stick their heads closer than 1 foot away from a painting or photograph.

Computer Monitors

The average computer monitor viewing distance is about 2.5 feet (762 mm). p@0.4 is 89 microns or about 300 ppi/dpi. p@1 is 222 microns or about 115 ppi/dpi. Now you can understand why most consumer computer monitors are about 100 ppi, and most professional computer monitors are slightly higher, but not by much.

The new iPad (3) has a resolution of 264 ppi, which isn’t as good as 300 dpi print but is much better than the average computer monitor. The new Eizo 36.4″ professional air traffic control 4K monitor is at 128 ppi.

Home television

Assuming the average viewing distance for television is 6 feet (1830 mm), p@0.4 is about 120 ppi and p@1 is about 50 ppi.

Most consumer large screen LCD and LED panels are about 50 ppi to 90 ppi, and average about 72 ppi. Now you know why. If your television gets smaller in size, then the higher ppi doesn’t really help. This is why 1920×1080 (at 100 ppi at 6 feet for a 50″ LCD/LED television panel) is good enough. The eye can’t really resolve a lot more at 6 feet.

Cinema

The width of a cinema screen can vary from 30 to 70 feet (360″ to 840″, 9144 mm to 21,336 mm). The closest viewing distance recommended is about 40 feet (3x height) – 12,192 mm. If one is projecting 2K on these screens, the ppi is about 2.4 ppi to 5.7 ppi. If one is projecting 4K, it is about 5 ppi to 11.4 ppi.

Is this what the eye needs?
p@0.4 works out to be 1.4 mm or 18 ppi.
p@1 works out to be 3.5 mm or 7 ppi.

As you can see, 4K comes very close to what the human eye can fully resolve in a cinema screen at average viewing distances. Obviously, many people sit in the front row, and they’d definitely appreciate higher resolution. Which is why we are moving towards:

8K and UHDTV

A 30 to 70 feet screen at 8K (8192 horizontal) gives me from 9.75 ppi to 22.8 ppi. This resolution beats what the eye can resolve at these distances. The future belongs to 8K.

But, to get 18 ppi (the best possible resolution) for a 70 feet screen, we’ll need a horizontal resolution of 15120 or 16K. This is about 128 Megapixels. Is anybody working on this?

• IMAX film is supposed to resolve between 10K to 12K (theoretical maximum)
• The Phase One IQ180 digital back is 80 Megapixels.
• The Red camera company did announce a 28K camera!

This is as good as it gets in 2012.

Takeaways:

• The maximum visual acuity of the human eye is 0.4 arc minutes.
• At 4 inches, the maximum the human eye needs is 2190 ppi/dpi.

Exclusive Bonus: Download my free cheatsheet (with examples) of the most important and useful focal lengths for film and video (PDF file optimized for mobiles and tablets).

## 25 replies on “Notes by Dr. Optoglass: The Resolution of the Human Eye”

Lucasays:

as others have said , you don’t show how the calculation works and what the viewing angle is, so how do you expect readers to understand how you got to 876 ppi?

duncansays:

what angle are you using to make your calculations? the angle of central or paracentral vision or a wider angle? as there is a great deal of differential between the signal quality generation between the different areas of the fovea which is not mentioned in your reference to visual acuity when considering the distance at which you are address. also where is the formula from there is no reference to that?

Sareeshsays:

There are other articles in the series.

morphinapgsays:

timwconnors or just use antialiasing to avoid jaggies

La pantalla 4K del Sony Xperia Z5 Premium, ¿es una estafa?says:

[…] el primer terminal Android con una densidad de pantalla casi humana. Digo esto porque el ojo humano es capaz de distinguir hasta 900 píxeles por pulgada, y el Z5 Premium se sitúa en 807. Menuda […]

jimv1983 Check out my articles on 4K TVs and whether you need 4K or 8K, you’ll find them interesting.

jimv1983says:

This just shows me even more that 4K is overkill.

I have pretty good vision, a little bit better than 20/20. According to this I can see about 75ppi at 6 feet.

I currently have a 55″ 1080p OLED TV. It has a pixel density of 40ppi. So, at a viewing distance of 6 feet having a 4K screen(assuming I’m watching 4K content) would make a difference. However, who sits 6 feet away from a 55″ screen? I sure wouldn’t. I currently sit 10 feet away from my 55″ (or 2.2x the screen size viewing distance). At that distance I wouldn’t be able to see 75ppi.

John Hodgsonsays:

Science Trumps Opinion

QHD and 4K Smartphones Are Impracticalsays:

[…] PPI of 538 is far beyond the maximum resolution that the human eye can recognize. There is a bit of controversy as to what the highest practical PPI is for a 5.5 inch screen held 12-18 inches away from the eye, […]

How Important Is Your Monitor? | The Digital Orientalistsays:

[…] In summary, it seems that at this moment in time for mobile you do well to get anything north of 300. For computers you are doing well with anything north of 200. Resolution of a screen has to do with the distance you are from it. From a distance, your eyes can only make out so much, but from up close you can see much more details.  You hold your mobile phone closer to your eyes than you would hold your monitor, so you need a higher resolution on your mobile phone. It seems PPI much higher than 300 could be well worth it, and there are already models out with far higher numbers, but at this moment, 300+ will do. Incidentally, 300 is what most magazines print on (measures in Dots Per Inch), so this is why we are now seeing a move towards 300. More reading here and here. […]

Ecranul Retina si pixelii pentru noi toti - Cum alegemsays:

[…] este c? Apple nu a spus de la ce distan?? nu po?i vedea pixelii, dup? cum a relevat un studiu de la acea vreme. Pe scurt, la o distan?? de 10 cm de ochiul uman, retina noastr? poate percepe […]

Ecranul Retina ?i pixelii pentru noi to?i |says:

[…] este c? Apple nu a spus de la ce distan?? nu po?i vedea pixelii, dup? cum a relevat un studiu de la acea vreme. Pe scurt, la o distan?? de 10 cm de ochiul uman, retina noastr? poate percepe […]

SwahiliWizzsays:

@Vimal Gopal
With your data (1920 x 1080 @ 50″ display, the pixel density is 44.06 pixels per inch (ppi), not 38.4 ppi.
See with online calculator here: http://pixeldensitycalculator.com/
Cheers.

[…] According to his article, Dr. Optoglass tells us that the perfect resolution of the eye can see 2190 PPI at 4 inches from the screen. However, none of us holds our phones that close to our faces, at least I hope you don’t, because that actually is bad for your eyes. In addition, the average visual acuity of a human is about 1 arc minute, which simply refers to a person with 20/20 vision. A person with 20/20 vision at 4 inches (the closest a healthy adult can focus) can see up to 876 PPI, which is considerably lower than the ideal eye, which can see at .4 arc minutes. […]

Don’t forget, as per the nyquist limit, you probably want to double the resolution so you don’t see jaggies in your diagonal lines.  This is why printed text on paper is *still* better than HiDPI screens.

Jojo323says:

Sareesh Sudhakaran
it would just be very very helpful if for one single example the actual numbers were put into the formula so we could see it. the article is great overall but because that is missing it is very hard to grasp

Jojo323says:

Sareesh Sudhakaran
What is Driving Miss Digital???

Jojo323 Please read the rest of Driving Miss Digital. It’s all there.

Jojo323says:

I don’t understand the angle part of this? The angle is never listed for any of these calculations. How does that part work? What angles are you putting into the formula. Can you post examples that enter specifics for all of the variables rather than just the screen size and distance?

Vimal Gopalsays:

Under the “Home Television” section, you mentioned that a 1920×1080, 50″ display is 100 dpi.  But, according to pxcalc.com, that combination only gets you to 38.4 dpi.  How are you getting 100 dpi??  Thanks.

Vimal Gopal The formula is available, Vimal. What results are you getting?

Too many Pixels? | The Smartphone Worldsays:

[…] with perfect 20/20 vision would theoretically be able to see individual pixels at a density of 2190ppi on a screen just 4” (~100mm) from their eyes, and for the average person with 20/20 vision, it’s about 876ppi. The […]

Too many Pixels? |SamMobilesays:

[…] with perfect 20/20 vision would theoretically be able to see individual pixels at a density of 2190ppi on a screen just 4” (~100mm) from their eyes, and for the average person with 20/20 vision, it’s about 876ppi. The […]