What Size Mini?

iPad mini with Retina Displays due out this fall?

Want.

Well, maybe.

When I’m holding my third generation iPad, I often wish it were my older son’s iPad mini. The eight-inch screen isn’t too much smaller, but the weight saving is spectacular. It also requires less elbow room on the airplane, which is no small thing (pun intended). But when I’m toying around with Preston’s mini, I usually find myself wishing I had the bigger display.

The question I guess is how Apple implements Retina in the mini.

One is simply to shrink the iPad’s ten-inch, 2,048-by-1,536 pixel screen down to 8 inches. Developers would love it, because then there would be only one iPad image size to worry about, and Apple would get some new bragging rights with an even more glorious-to-look-at screen.

But it presents a couple of problems, too. First, that pixel density would be extremely expensive and difficult to produce. Apple got hammered for lower profit margins last quarter, which was due in large part to the lower-margin mini cannibalizing sales from the full-size iPad. That pixel density comes with another cost, too: Battery. Pixels packed that tightly require a much brighter backlight. And that means sacrificing either battery life or tablet size. The former is a big no-no to Apple’s way of thinking, and the latter takes the “mini” out of “iPad mini.”

The other way to achieve Retina density would be to produce the exact same panel used in the full-size iPad, but cut down to mini proportions. “Retina” is determined by pixel density in a given space at a given distance, not by total pixel count. My back-of-the-envelope math says this new mini screen would have a narrow-side resolution of about 1,000 pixels — which is nearly “1080p” worthy. Apple would also gain some very nice economies of scale, since they’d only have to produce one kind of iPad panel, but merely cut into two different sizes.

The problem with this route is that “nearly.” Nearly HD ain’t HD, which seems a ridiculous compromise to make on an eight-inch tablet — especially when there are five-inch phones that display 1080. Also, 1,350 x 1,000 or whatever pixels is just a weird size.

Then there’s what I’m calling in my head, “1080p Plus.” The iPad (correctly) uses a 4:3 screen, just like an old lo-def TV. So what if Apple made the wide-side resolution exactly 1,920 — just like a new HD TV. But then there’s all that extra leg room at the bottom, for a narrow-side resolution of about 1,400…

Wait… 1,920-by-1,400 is almost identical to the big iPad’s 2,048-by-1,536. And it doesn’t make any sense at all to produce two completely different (yet equally expensive) LCD panels. The economies of scale just don’t add up.

Best guess: The Retina Mini will have the exact same resolution as the ten-incher. If Apple can pull of that feat without sacrificing weight, size, or battery life, they’ll have achieved something I would have thought was impossible just a year or two ago.