I thought maybe the most interesting single thing about the new iPhone 4 was its display, not so much the 960 vertical dots but the 326DPI, in the cleverly-named Retina Display. Which leads me to wonder, how much does this matter?

300 · If you care about this subject, I recommend a quick trip to Wikipedia’s List of displays by pixel density. In the keynote, Steve claimed that there was some sort of a threshold around 300DPI having to do with the resolving capabilities of the human retina (thus the name).

Indeed, three hundred is an interesting number; the first wave of personal-computer printers which produced results that actually looked really good started at 300DPI. Right now, per Wikipedia, there are exactly three devices in the world whose displays exceed it; along with the iPhone, the Toshiba G900 and the Sony/Ericsson Experia X1, both WinMo phones.

Also I can testify that my Nexus One, at 250DPI or so, is astoundingly sharp; the first thing in years that’s made me want to tune up the typography on my blog.

Take Me Higher · At the same time, I’m not sure about the importance of that 300DPI elbow. It’s sure not there on paper; today’s commercial laser printers commonly run at 1200 or 2400DPI. And high-end commercial pre-press products go way higher; the devices in the Heidelberg Prosetter family range up to 3386DPI.

Given the nature of the Android ecosystem, I think we can be pretty sure that if it turns out that Apple bet right and the extra resolution is a good selling point, we’ll be in an amusing arms race around DPI PDQ.

Do We Even Need It? · I hope so, because I sure love the look of these things, but I’m not 100% convinced. I’m typing this on a generic Dell 30" 2560x1600 display offering a pathetic 101DPI, and for the stuff I do all day, it makes me very happy; I’d have a hard time sacrificing any of that real-estate (4,096,000 pixels!) for higher density.

For serious photo-work I use a 25" NEC 2690 that I bought because it was good enough for James Duncan Davidson, and everything looks immensely better there than it does on the big Dell or my 113DPI MacBook, but that’s not because of the 98DPI, it’s because of the wonderful color.

I suspect that unless you’re preparing high-quality print work, there’s no appreciable benefit for a photographer, and perhaps some downside, in an ultra-high-res display.

Some other relatively low-res devices that seem beautiful to me: the iPad at 132DPI, and my nice 42" 1080p TV at home, at a laughable 52DPI.

I gotta say though that those high densities are a joyful experience on hand-held devices; is it as simple as the fact that you hold them closer to your face? Is there a placebo effect at work?

Economics · Do bear in mind that all these extra dots are not free. I’m fairly ignorant about the manufacturing trade-offs, i.e. how much extra it’s costing Apple to put 614,400 dots on the iPhone 4, as opposed to the the 3GS’s 153,600.

I tend to worry more about the software costs; you have to manipulate 4 times as many pixels every time you double the DPI, and while we’ve learned a lot of tricks over the years, and increasingly push the work down into display controllers, the computing cost is very far from zero.

Typography · Anyhow, the best way to make a good looking page on the screen, particularly now that browsers are getting smarter and more polished with their font-handling, is with good typography.