Jobs wasn’t falsely advertising the iPhone’s capabilities at all. … But a lot of people read the headlines and it taints their view; someone reading that article may be more likely to think Jobs, once again, has overblown a product to excite people. He didn’t.
Plait was talking about an article on Wired, which cited display expert Raymond Soneira, who argued that 477 ppi would be necessary to match the human retina at a distance of 12 inches.
Meanwhile, I was arguing for 1060 ppi, at 10 inches! Who’s right?
In a way, we all are. Again, I think the Clarkvision site has the clearest explanation of the research:
Blackwell (1946) derived the eye’s resolution, which he called the critical visual angle as a function of brightness and contrast. In bright light (e.g. typical office light to full sunlight), the critical visual angle is 0.7 arc-minute (see Clark, 1990, for additional analysis of the Blackwell data). The number above, 0.7 arc-minute, corresponds to the resolution of a spot as non-point source. Again you need two pixels to say it is not a point, thus the pixels must be 0.35 arc-minute (or smaller) at the limit of visual acuity.
In other words, at 0.7 arc-minutes, you can tell that a light source is not a point. So an 0.7-arc-minute pixel would be too big. Therefore, Clark argues, for a pixel to match the resolution of the retina, it must be half this size — 0.35 arc-minutes. Meanwhile, Soneira says a pixel need only be .6 arc-minutes. We know a .6 arc-minute pixel is indistinguishable from a point — you don’t have to go as small as 0.35 arc-minutes, so that makes some sense.
But Clark cites other research with converging evidence that we see pairs of objects at a resolution of 0.7 arc-minutes. That means single objects (pixels) need to be half that size. Plait counters with a Wikipedia link claiming 1.2 arc-minutes. Who’s right?
It’s hard to say, but in any case, these studies are all measuring something very different from what you use your computer display to do. They’re testing your ability to see lines, dots, or other very simplified figures. Why not study actual pictures, or actual text?
In fact, Clark did exactly that. He had viewers sort pictures printed at 150, 300, and 600 ppi. They could successfully sort the pictures from lowest- to highest-resolution. Thus, it’s quite clear that the 326 ppi of the iPhone 4 doesn’t display the highest resolution detectable by the human eye in realistic conditions.
Calling the new iPhone display the “Retina Display,” therefore, is an exaggeration at best.