As blogger excitement reaches a fever pitch over the iPhone 4 — now available for pre-order, if you can get the website to work — confusion and rage are also running wild. Why? Because of Steve Jobs’ claim that the iPhone 4’s new “Retina” display offers higher resolution than the human eye does.
The mathapalooza began a few days ago when PC World interviewed Raymond Soneira, who has a PhD in theoretical physics and runs a firm that makes high-end software to test computer displays. Soneira explained that it’s hard to test Jobs’ claims because we see pixels only when we’re close enough to the screen. Sit 20 feet away from your laptop or TV and no one can see the pixels — so at 20 feet, it is “better” than your eye. But sit 6 inches away and you’ll certainly see them — so at 6 inches, it is not. “Better” is subjective and dependent on distance.
And that’s the mystery of the iPhone 4: Jobs said that at a foot, the 326 pixels per inch that the phone offers are better than the eye can parse. Soneira said that’s not the case: At 12 inches, based on the “angular measurement” of how the eye actually works (click PC World’s story for the full math, if you dare), the eye can really manage 477 pixels per inch. Not until you’re 18 inches away from the screen will the pixels entirely disappear.
Case closed? Not quite. The folks at Discover magazine busted out their protractors and reached a different conclusion, that Jobs was right. How so? Because, as Discover notes, the numbers used by Soneira assume you have perfect vision. Discover knocked the estimates down considerably, saying that if you have “typical” vision, you will not see pixels on the iPhone 4 when held 12 inches from your face.
End of discussion? Certainly not. I pay a lot of money to my optometrist to ensure I have near-perfect vision, but the quality of glasses prescriptions, like eyes themselves, will vary widely. Even the definition of “perfect” is subjective, as any Lasik enthusiast can tell you. The bottom line is that some people are going to see the pixels on the new iPhone, and some are not. I also doubt that users will be holding rulers next to their faces as they look at their cell phones’ screen (although I know I will, just to see) to hold Jobs to his word.
And what if, in the end, he’s lying after all? Well, it’s not like anyone’s going to throw lye in his eyes for his transgression.
UPDATE: Raymond Soneira sent this note with additional information about his comments. I reprint it below verbatim.
Steve Jobs’ statement on the “Retina Display” when announcing the iPhone 4 at WWDC: “It turns out there’s a magic number right around 300 pixels per inch, that when you hold something around to 10 to 12 inches away from your eyes, is the limit of the human retina to differentiate the pixels.”
I used the accepted value for the visual acuity of the Retina (see below) and found that the iPhone was more than a factor of 2 short on pixels to be a Retina Display. The iPhone 4 would need to have 1.3 megapixels instead of 0.6 megapixels to be a true Retina Display at 12 inches. At 10 inches it would need even more – 1.9 megapixels – a factor of 3 short.
There have been some comments that my analysis is for perfect vision. Jobs’ statement is for the *Retina* not the *Eye* with 20/20 or other vision. For 20/20 vision the accepted value is to resolve two lines that are separated by 1.0 arc minute. In that case a 20/20 vision display needs a resolution of 286 dpi or higher at 12 inches and 344 dpi at 10 inches. The iPhone 4 has 326 dpi, so at 12 inches it is a 20/20 Vision Display but not a Retina Display.
In fact, there are lots of people who have better than 20/20 vision, for example, 20/10 vision is twice as good as 20/20. I had 20/10 vision until I was 20 years old and corrective lenses can provide 20/10 vision for many people. For 20/10 vision the acuity is 0.5 arc minutes, which is actually smaller than the value used for the Retina, so at 12 inches an iPhone 4 is not a 20/10 Display nor a Retina Display.
One article examining my results that got a lot of attention was by Dr. Phil Plait on Discovery Magazine.com. He is an astrophysicist and verified my calculations but concluded that while I was technically correct I was being very picky and my results only applied to people with perfect vision – by that he meant 20/20 vision, which is nominal good vision, but not 20/10 vision, which is considered perfect vision. My point is actually that specs have to be picky.
Specs need to be objective, precise and accurate. Allowing puffery and exaggerations in the sales and marketing starts a snowballing effect that eventually leads to the 1000 percent rampant spec abuse that I document for displays. The iPhone 4 is a fabulous display, it’s just not a Retina Display – but it’s good enough for 20/20 vision when held at 12 inches or more from the eye. Since Apple makes great products that have excellent specs it will be a lot better for them if everyone sticks with the true objective values instead of values exaggerated by marketing departments.
— Christopher Null is a technology writer for Yahoo! News.
