One of the key points Steve Jobs stressed during his WWDC Keynote was the iPhone 4′s impressive new retina display which sports a resolution of 960×640 and a ppi of 326. But why the name Retina Display, you ask? Well, Jobs stated that the human eye can only differentiate pixels up to 300 ppi, thereby making the iPhone 4′s high-res display more powerful, so to speak, than what the human eye can detect.
While Apple’s new display certainly sets a new standard when it comes to quality, some are curiously taking issue with Apple’s claim about the quality of the iPhone 4 display, along with Apple’s retina claims.
First up, Samsung immediately dismissed Apple’s efforts at quadrupling the iPhone’s resolution, opining that doing so only improves clarity by a scant 3-5%. Moreover, a Samsung spokesman said that increasing the resolution as Apple did could potentially battery drain by as much as 30%. Their take away? Well, whatdya know, they were busy touting AMOLED screens which they argue are better because they don’t need a blacklight while noting that they “make up for any resolution loss in other ways, such as higher contrast with true black, more accurate colors and no limits on viewing angles.”
“Structurally, [Apple's] IPS LCD technology cannot catch up with AMOLED display technology,” a Samsung representative told the Korean Herald.
But as for the Retina Display itself, Raymond Soneira of DisplayMate Technologies got the ball rolling last Wednesday when he challenged Apple’s claim that the iPhone 4 display was so dense that it outweighed the human eye’s ability to differentiate between pixels.
Soneira wrote to PC Mag:
The resolution of the retina is in angular measure – it’s 50 Cycles Per Degree. A cycle is a line pair, which is two pixels, so the angular resolution of the eye is 0.6 arc minutes per pixel.
So, if you hold an iPhone at the typical 12 inches from your eyes that works out to 477 pixels per inch. At 8 inches it’s 716 ppi. You have to hold it out 18 inches before it falls to 318 ppi.
So the iPhone has significantly lower resolution than the retina. It actually needs a resolution significantly higher than the retina in order to deliver an image that appears perfect to the retina.
Yeah, we don’t get it either.
But Soneira went on to explain to Wired that while the iPhone display is close to being perfect, “Steve pushed it a little too far.” Soneira went on to say that Jobs’ assertions were outlandish and reeked of false marketing.
Soneira, who possesses a Ph.D. in theoretical physics from Princeton and has been studying displays for 20 years, said it was inaccurate to measure the resolution of the eye in terms of pixels, because the eye actually has an angular resolution of 50 cycles per degree. Therefore, if we were to compare the resolution limit of the eye with pixels on a screen, we must convert angular resolution to linear resolution. After conversions are made, a more accurate “retina display” would have a pixel resolution of 477 pixels per inch at 12 inches, Soneira calculated.
Not to be outdone, Jim Darlymple of The Loop contacted a vision scientist last week to get his take on the Retina Display “controversy”.
This is what PH.D William H.A Beaudot, a vision scientist who formerly conducted research at McGill University in Montreal and founded KyberVision had to say.
In my opinion, Apple’s claim is not just marketing, it is actually quite accurate based on a 20/20 visual acuityA visual acuity of 20/20 means that a normal human eye can discriminate two points separated by 1 arc minute (1/60 deg). A visual angle of 1 arc minute seen from a distance of 1 foot corresponds to a dot size of about 89 micrometers or a pixel density of 286.5 dpi. Since the “Retina” display has a pixel density of 326 dpi (14% better than what we would expect from a 20/20 visual acuity at 1 ft), it would seem unfair and misleading to refute Apple’s marketing claim on this basis.
Since this display is able to provide a visual input to the retina with a spatial frequency up to 50 cycles per degree when viewed from a distance of 18-inches, it almost matches the retina resolution according to the Nyquist-Shannon sampling theorem,” said Beaudot. “As such, Apple new display device can be called without dispute a Retina Display. Could it get better? Sure, but so far this is the closest thing ever done in display technology for the consumer market that matches the human retina resolution.
And finally, Phil Plait, who, you know, “spent a few years calibrating a camera on board Hubble” strongly disagrees with Wired’s headline exlcaiming that Apple’s Retina Display is false marketing, while “mildly disagreeing” with Soneira’s claims.
Jobs claims the iPhone held at 12 inches from your face has pixels too small to be resolved by your eye. Soneira, the display expert quoted in the magazine articles, disputes that. He uses the 0.6 arcmin resolution for the human eye (so we use the scale factor = 5730). Let’s use that and run the numbers.
Something 12 inches away means your eye can resolve dots that are bigger than
12 inches / 5730 = 0.0021 inches
So if the pixels on the iPhone are smaller than 0.0021 inches in size, then Jobs is right. Your eye won’t resolve them. If the pixels are bigger, Soneira is right, and your eye can resolve them.
The actual iPhone 4 has 326 pixels per inch (the display is 960 pixels high, and about 2.9 inches in length). You have to flip that to get the size of the pixel in inches:
1 / 326 = 0.0031 inches
Uh oh! Things look bad for Jobs. The iPhone pixels are too big! At one foot away, your eye can resolve the pixels, and Jobs must be lying!
Or is he? Remember, Soneira used the 0.6 arcmin resolution of the eye, but that’s for perfect eyesight.Most people don’t have perfect eyesight. I sure don’t. A better number for a typical person is more like 1 arcmin resolution, not 0.6. In fact, Wikipedia’s lists 20/20 vision as being 1 arcmin, so there you go.
If I use 1 arcminute instead, the scale factor is smaller, about 3438. So let’s convert that to inches to see how small a pixel the human eye can resolve at a distance of one foot:
12 inches / 3438 = 0.0035 inches
Aha! This means that to a more average eye, pixels smaller than this are unresolved. Since the iPhone’s pixels are 0.0031 inches on a side, it works! Jobs is actually correct.
[Note: in the articles about all this, they used units of pixels per inch, whereas I've used the size of the pixels themselves. You can flip all these numbers to convert. The iPhone4 has a resolution of 326 ppi (pixels per inch). Soleira says the eye can resolve 1 / 0.0021 = 477 ppi. However, normal vision can see at 1 / 0.0035 = 286 ppi. So the density of pixels in the iPhone 4 is safely higher than can be resolved by the normal eye, but lower than what can be resolved by someone with perfect vision.]
3) So what does all this mean?
Let me make this clear: if you have perfect eyesight, then at one foot away the iPhone 4’s pixels are resolved. The picture will look pixellated. If you have average eyesight, the picture will look just fine.
So in a sense, both Jobs and Soneira are correct. At the very worst, you could claim Jobs exaggerated; his claim is not true if you have perfect vision. But for a lot of people, I would even say most people, you’ll never tell the difference. And if you hold the phone a few inches farther away it’ll look better.
So in my opinion, what Jobs said was fine. Soneira, while technically correct, was being picky. So I mildly disagree with him about that…
Still, the headline used by Wired.com was clearly incorrect; Jobs wasn’t falsely advertising the iPhone’s capabilities at all… So, in this case, I hope I’ve…
[wait for it, wait for it]
… made things clear.
So what have we learned from this pointless saga? Absolutely nothing. Except, maybe, that nerds will get down and dirty and argue about anything, and that these scientific analyses of Apple’s high-res display are way over our feeble little heads. But whether or not the human eye can detect individual pixels on the iPhone 4′s new screen is beyond the point. What matters is that the display is, by all accounts, the highest quality display to ever hit a mobile device. Ever. People who’ve seen it can’t stop raving about it, and it’s high time the nerds stop bickering about inconsequential details.