Bad Astronomy: Resolving the iPhone resolution

In other words, at 12 inches from the eye, Jobs claims, the pixels on the new iPhone are so small that they exceed your eye’s ability to detect them. Pictures at that resolution are smooth and continuous, and not pixellated.

However, a display expert has disputed this. Raymond Soneira of DisplayMate Industries, was quoted both in that Wired article and on PC Mag (and other sites as well) saying that the claims by Jobs are something of an exaggeration: “It is reasonably close to being a perfect display, but Steve pushed it a little too far”.

This prompted the Wired article editors to give it the headline “iPhone 4’s ‘Retina’ Display Claims Are False Marketing”. As it happens, I know a thing or two about resolution as well, having spent a few years calibrating a camera on board Hubble. Having looked this over, I disagree with the Wired headline strongly, and disagree (mildly in one case and strongly in another) with Soneira. Here’s why.

Jobs’s claim is 300 dpi at 12 inches. I remember this as 600 dpi at the nearpoint of ~6 inches (15 cm), which is the same angular resolution. Closer than this and most adults can’t focus; your nearpoint is generally larger if you are older. Which is the same claim, and an explanation as to why 300-600 dpi is generally considered photo quality for images that are printed, and 1200 dpi is the highest resolution you’d ever need.