The perceived "visual density" of a screen—and thus the amount of anti-aliasing possibly needed to make computer graphics look convincing and smooth—is dependent on the pixel density of the screen (the "ppi") and the distance from the user's eyes.
Adjust values below to calculate the visual density, or select a different value to control and instead enter the desired ppd.
- pixels per degree (ppd) at center (~123 at edge)
|For 30 ppd you need||or||or||20/40 vision; poor vision|
|For 60 ppd you need||or||or||20/20 vision; below average vision|
|For 80 ppd you need||or||or||20/15 vision; average vision limit 1, 2|
|For 120 ppd you need||or||or||20/10 vision; practical upper limit of visual acuity|
|For 150 ppd you need||or||or||20/8 vision; theoretical upper limit of visual acuity 3|
|For 200 ppd you need||or||or||20/6 vision|
|For 240 ppd you need||or||or||20/5 vision|
|For 300 ppd you need||or||or||20/4 vision; approx. limit of alignment detection (hyperacuity) 4|
|For 2400 ppd you need||or||or||approx. limit of high contrast feature detection 4|
"20/20" vision (or "6/6" in Europe) corresponds to being able to resolve details 1 arcminute in size, or 60 pixels per degree. This is defined as the "normal" visual acuity for adults, but it is actually not the average. While visual acuity changes per person and over time, the average acuity in adults is about 1.6 times better than 20/20, roughly 20/15 vision, or 80ppd. Visual acuity peaks at around 25 years old and then slowly declines, but even then the average 75 year old has better eyesight than 20/20. Really.12
Seeing details at 120ppd is equal to "20/10" vision (or "6/3" in Europe). The graph on page 489 of 1 shows that only one or two individuals in the 100+ of tested 17-18 year olds got close to this limit (shown as -0.3 logMAR). Anecdotally, my eye doctor told me that in all of his 20+ years in practice he has only seen one person (a teenager) who measured at this level without glasses. However, corrective eyewear can often achieve this level. For example, American baseball star Mark McGwire is widely reported to use contact lenses that improve his 20/500 vision to be better than 20/10 5.
Distinguising details at 150ppd would require 20/8 vision. According to 3 the theoretical upper limit of human visual acuity lies somewhere between 20/10 and 20/8 vision.
According to 4 hyperacuity can differentiate misaligments as small as 8 arcseconds (450ppd). This same entry describes
The smallest detectable visual angle produced by a single fine dark line against a uniformly illuminated background is also much less than foveal cone size or regular visual acuity. In this case, under optimal conditions, the limit is about 0.5 arc seconds. This corresponds to about 7200ppd. Both of these statements on Wikipedia have no citation, but are roughly backed up by 6.
The lower values of 300ppd (12 arcseconds) and 2400ppd (1.5 arcseconds) limits described above are based on the fact that these limits are heavily dependent upon contrast, and electronic displays may not provide the same level of contrast as may be perceived in a well-lit real-world environment. For example, the binary star Sirius is the brightest star in the night sky, but is only 0.006 arcseconds across from our perspective. This corresponds to feature detection of a detail so small that it corresponds to 600,000ppd. However, no monitors can give off the light per pixel of a burning star the size of our sun, let alone two of them. You can test your own hyperacuity using the Freiburg Vision Test. Be sure to calibrate your monitor, standing far enough from it that the test calibration passes.
A good introduction to these topics—along with accessible, in-depth discussion of the physics—can be found in 7.
- J. Ohlsson and G. Villarreal, Normal visual acuity in 17–18 year olds, Acta Ophthalmologica Scandinavica, 2005, pg. 490. PDF
- D. B. Elliott, K. C. H. Yang, D. Whitaker, Visual acuity changes throughout adulthood in normal, healthy eyes: seeing beyond 6/6, Optom Vis Sci. 1995 Mar; 72(3):186-91. PDF
- R. Applegate, Limits to Visition: Can We Do Better Than Nature, Journal of refractive surgery (Thorofare, N.J.: 1995), 16(5):S547-51. PDF
- Wikipedia, Visual Acuity, Other Measures. link
- Softchrome Sports Vision, online. link
- S. A. Klein and D. M. Levi, Hyperacuity thresholds of 1 sec: theoretical predictions and empirical validation, Journal of the Optical Society of America, 2:1170–1190. PDF
- M. Kalloniatis and C. Luu, Visual Acuity, Webvision, The Organization of the Retina and Visual System, Online Textbook. link
Copyright ©2014–2017 Gavin Kistner and NVIDIA, Inc.