One of the most exciting features of the iPhone 4 is the Retina Display, which at 326 ppi exceeds the limits of human’s retina, thus making it impossible to see pixels on screen.

Raymond Soneira, president of DisplayMate Technologies (Ph.D. in theoretical physics from Princeton, displays expert) told Wired that Steve pushed it too far. The Retina Display is a misleading marketing term, he says.

“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.

He noted, however, that he was confident Apple will have the best phone display on the market. Like the iPad’s LCD display, the iPhone 4’s screen features In-Plane Switching technology, in which crystal molecules are oriented so their motion is parallel to the panel rather than perpendicular. For viewers, the result is a very wide viewing angle — up to 180 degrees — with brilliant color. Soneria added that we might not realistically need anything better than 326 ppi.

For comparison, glossy magazines are typically printed at 300 dots per inch.”

But, the Bad Astronomy took some time to explain the resolution problem, and it turns out that Jobs might be right indeed:

“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 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.

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 there you have it, the Retina Display will look perfect to most people and people with perfect eyesight will be able to see some pixels. I wouldn’t call it misleading marketing, Mr. Soneira.