Screen - Retina Display

Right out of the box, the iPhone 4's new 326 PPI, 960x640, 3.5" display is arguably the single most striking change the new iPhone brings. In a word, it's dazzling. Text and high res images look amazingly sharp on the iPhone 4’s retina display. It’s an improvement over the 800 x 480 AMOLED screens that have been shipping on most Android phones. But if you’re comparing it to an iPhone 3GS the difference is huge.

iPhone 3GS
iPhone 4

Text on the Google Nexus One

Text on the iPhone 4

The dot pitch is truly remarkable, so much so that Apple makes the claim that their display outresolves the human eye; its advertised ability to do so has earned it a new Apple tradename, "retina display."

Text on the HTC EVO 4

Text on the iPhone 4

AnandTech Logo on the EVO 4G

AnandTech Logo on the iPhone 4

Immediately after hearing Apple's claim that the Retina Display outresolves the human eye, I snapped into optics mode and crunched the numbers, and tweeted that the results were valid.

In the days that followed, there was considerable debate about the validity of Apple's claims. However, nearly all of the debate really just hinged on a debate over angular resolution of the human eye, and a little more over viewing distance. They're both entirely conventions.

As you've probably discovered by now, the human eye resolution can really only be characterized in angular subtense. Hold something closer to your eye, and you can see smaller features better (in theory), move it further away, and you can't make out small spatial details. The minimum angle visible with the human eye is the angle at which features (for the most common definition, a black and white square wave) stop being visible, and are indistinguishable from each other.

Most measures of visual acuity test with this implicitly - the Snellen eye chart's use of the capital "E" is literally a perfect example, which has given rise to a "tumbling E" eye chart. At twenty feet, the capital E subtends 5 minutes of arc, and conveniently has five half cycles of white to black (from top to bottom). So 20/20 implicitly implies an angular resolution of 1 arcminute (1/60 degrees).

As an Optical Sciences and Engineering undergrad, I've had 1 arcminute drilled into my head more times than I can count as being the "normal" angular resolution of the human eye system. In practice, this is 20/20 vision, which is "normal," yet not perhaps the absolute maximum for human perfection. We can play games of course and argue that a small subset of the population has better than normal uncorrected vision, and thus an angular resolution of below 1 arcminute. I have above average uncorrected vision, which I've measured to be 20/15 on average, giving an angular resolution of approximately 0.75 arcminutes. Of course, the definitions stem from the spacing of cones in the fovea, the highest resolution part of the retina.

The other informational quantity needed to test the Retina Display claims is viewing distance. Again, there's a commonly agreed upon convention - standard viewing distance is considered to be 1 foot. This is another drilled into my brain number tossed around for comfortable viewing and reading. In practice, you can focus on objects much closer to your eye - this is called the near point and is often given as 10 inches, though as you get closer you increase strain aren't likely to keep it here.

Maybe not exactly the limit, but close enough.

Given the two most common standards tossed around, 1 arcminute and 12 inches, do the math out and you'll arrive at around 286 pixels per inch as the limit for eye resolving power, comfortably below the 326 on the Retina Display. Move to 0.75 arcminutes at 12 inches, and it's 382 pixels per inch, higher than the Retina Display. Honestly, I can't see the pixels at 12 inches.

Of course, the real story is even more complicated. Remember how the definition comes with the implicit assumption that we're dealing with a square wave pattern from white to black? That's a factor too - the contrast of the two pixels. Lower the contrast, and the eye's ability to pick out features decreases even more. So far, everything we've talked about has been first order, and without aberrations. Toss in spherical and astigmatism, two aberrations common to the eye system, and eye performance drops way more.

The human eye system is actually pretty poor, and shockingly easy to outresolve. In fact, if you saw the image your eye forms on your retina, you'd likely be appalled; it's your brain that makes the system usable. But at the end of the day, Apple's claims that the display outresolves the human eye are good enough for us.

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  • philosofa - Wednesday, June 30, 2010 - link

    This kind of in-depth and insightful review is exactly why I read pretty much every Anandtech article (that and a liberal workplace when it comes to browsing lol). Cheers very much Brian & Anand. Don't feel a huge urge to upgrade from my 3GS, but it does look like a pretty damn fine smartphone!
  • quiksilvr - Wednesday, June 30, 2010 - link

    Yeah, but he's holding it wrong :(
  • medi01 - Wednesday, June 30, 2010 - link

    But guys, who do you pay a fortune for these phones? If you'd buy iphone or whatever phone with 2 year contract in most of Europe you'd pay just the price of the phone over 2 years (a bit more, in case of iphones it's about 700 Euro)

    I mean, aren't there cheaper contracts? I could imagine, that you can't buy some models other than from mobile providers, but hey, there are other countries with online shops.
  • Snotling - Thursday, July 1, 2010 - link

    In north America and even more in Canada, there is a lot of territory to cover and lower population density. Cellular networks need to plant antennas where there is theoretically too few users to pay for it.
  • JimmiG - Thursday, July 1, 2010 - link

    Sweden is kind of like a smaller version of Canada. Apart from the three major metro regions (Stockholm, Malmo and Gothenburg), the country is very sparsely populated. An average city is maybe 50,000 people. Yet we have extremely affordable plans by comparison.. I mean like less than $10 for a perfectly usable plan (1GB of data or so) and no more than $20 for 5GB or even Unlimited. Paying $100 a moth..geez. I barely pay that in a year.
  • Ratinator - Friday, July 2, 2010 - link

    Sorry, I think that is a bad comparison.

    Sweden is 2/3rd the size of the province of Saskatchewan and 9 times the population of Saskatchewan as well. You can't even compare Sweden to the province of Saskatchewan let alone Canada. You have roughly 13.5 times the population density of that province. Mind you this is probably least densely populated of the provinces (not territories) Maybe not the best example, but lets look at a better one.

    You could maybe compare to Ontario (our most populated province) however, you are less than half their size with 80% of their population. When calculated out you still have almost twice the population density of our most populated province.
  • ABR - Monday, July 5, 2010 - link

    It's pretty hard to find countries with similar population density to Canada, ranked 228 out of 239 in the world according to wikipedia. On the other hand, most of the country is inaccessible by road and I seriously doubt you are putting up cell towers in Nunavut. On the other hand Finland has half the population density of the United States and yet has similar cellular and broadband rates to Sweden. We don't know what it is with North America, whether a lack of competition, cartel agreements, or all the companies being weighed down by historical investments, but you guys do lead the world in what you pay for communications.
  • Guspaz - Wednesday, October 12, 2011 - link

    According to the CIA world factbook (yes, I use a foreign agency's site for info on my own country), 90% of Canada's population lives within 160km of the US border.

    If we make an estimated measurement and take the southern border's length at 6416 km, multiply that by 160 and you get an area of about a million square kilometres with a population of, adjusting for the 90%, about 31 million. That would be an actual density in that region of about 31 people per square kilometre.

    That puts us in 180th place, right behind the US in 179, which has a density of 32. This is close enough to say that, within our populated region, we've got about the same population density as the US.
  • ripwell - Saturday, July 3, 2010 - link

    Are you comparing data plans to voice and data plans? Telia was blasted when the iPhone first came out with some of the most expensive plans in the world. It's pretty amazing if you're suggesting that you can now get voice and data for just $10 a month.
  • JimmiG - Sunday, July 4, 2010 - link

    "It's pretty amazing if you're suggesting that you can now get voice and data for just $10 a month. "

    You rarely get pre-paid minutes here unless you really want to. You just pay about $6 a month and get billed for your minutes afterwards. In my case, it's about 10¢ per minute, but to phones on the same network, you get unlimited texts, mms's and minutes. Yes, for $6 a month. That includes most of my friends and relatives that's pretty much what I pay for voice and texts.

    Then on top of that, you can add your data plan, for example 1GB a month at 6Mb is $9 (add $7.8 for 5GB at 10Mb/s).

    -Or, if you really must go crazy, you can get 3,000 minutes for $65. Combined with 5GB/month at 10Mb/s, you're paying roughly $82. That's the absolute maximum. No subsidized phone, but you get over 3x more minutes than the iPhone deal and 2.5x the amount of data. The phones aren't really subsidized at all when you look at the total cost.

    "You could maybe compare to Ontario (our most populated province) however, you are less than half their size with 80% of their population. When calculated out you still have almost twice the population density of our most populated province. "

    But what about the US? Its population density is 32/km2 vs 20.6/km2 for Sweden. There are definitely states that are comparable in size and population density.

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