JVM Research and Technology
Retina Displays
Perceived image data discrimination may be limited by the combination of pixel density, observer visual acuity, contrast, and viewing distance.
The often accepted limit of human vision for a person with 20/20 visual acuity is to discriminate a span of one arc minute of subtended angle. One arcmin is 60 arc seconds or 1/60 degree.
e.g. Campbell and Green say we can resolve 60 cy/degree, or 1 arcmin.
Assuming a constant reasonable constrast, the real key is the viewing distance.
The following Apple products have displays which are marketed to be retina displays.
- iPod Touch / iPhone 4 & 4s = 326 DPI, pixel pitch = 0.003058"
- iPad 3 & 4 = 264 DPI, pixel pitch = 0.00377"
- MBP with Retina display = 220 DPI, pixel pitch = 0.00455"
Where dpi = 1/pixel pitch (distance between pixels) in inches.
ϴ = {tan-1[1/(dpi * distance)]/4}
Accordingly, to qualify as a Retina display, the angle theta (ϴ) from the viewing point to the distance equal to the pixel pitch must be ≤ 16.667 E -3 degrees.
Analysis 1: Let's assume a viewing distance of 12 inches.
| Product |
DPI |
pp (in) |
dist (in) |
ϴ (º) |
ϴ ≤ 16.667 E -3
? |
| iPhone 4/4S | 326 |
0.003058 | 12 |
0.00366 |
yes |
| iPad3 |
264 |
0.00377 | 12 |
0.004521 |
yes |
| MacBook Pro |
220.53 |
0.00453 |
12 |
0.005413 |
yes |
| 24.1" 1920x1200 Monitor |
94.34 |
0.0106 |
12 |
0.01265 | yes (marginally) |
According to the above results, even a 24.1" 1920x1200 monitor qualifies as a retina display at 12", as the pixels are small enough to be beyond the limit of perceptability at 60 arcsec.
Analysis 2: If we change the viewing distance to 6 inches, we get these results.
| Product |
DPI |
pp (in) |
dist (in) |
ϴ (º) |
ϴ ≤ 16.667 E -3
? |
| iPhone 4/4S |
326 |
0.003058 | 6 |
0.007323 |
yes |
| iPad3 |
264 |
0.00377 | 6 |
0.009043 |
yes |
| MacBook Pro |
220.53 |
0.00453 |
6 |
0.010825 |
yes |
| 24.1" 1920x1200 Monitor | 94.34 |
0.0106 |
6 |
0.02531 | no |
| Reference |
100 |
0.01 |
6 |
0.23873 | no |
Now the ~100 dpi display and exact 100 dpi reference (both with the red backgrounds in the table cells) no longer pass the definition of Retina
displays, but the 3 Apple "Retina" displays still do.
Since viewing distance is component of what may be considered a "Retina" display, then clearly we can reduce to the viewing distance to a point where none of the displays can be consider to be a retina display, however unrealistically close to a person's viewing distance the distance may be.
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