27” Retina Math marco.org

Marco-Dot-Org reader Adam Lacy writes to Mr. Dot-Org:

I was reading an article about the new 84” Toshiba 4K TV and it got me thinking about how 4K relates to Retina Display PPIs. I wanted to speculate on the possibilities for the future iMac/Cinema Displays. In doing so I came across some interesting math.

4K = 3840 × 2160

If you work out the PPI for 4K at 27 inches it conveniently comes out to 163 PPI.

If 163 pixels per inch sounds familiar to you, that’s because it’s the pixel density of the original-through-3GS iPhone, and the rumoured iPad mini. How convenient.

Since the current Retina MacBook Pro can drive its internal display in addition to two Thunderbolt displays (12.5 megapixels), 4K video (8.3 megapixels) would already be possible in lid-closed mode. A 27″ Retina iMac would be possible at this resolution.

Marco Arment concurs:

It would barely qualify as “Retina”, but if it had a scaling mode to give me the same space as 2560 × 1440 (much like the Retina MacBook Pro’s simulated 1680 × 1050 and 1920 × 1200 modes), I’d take it.

I agree that it’s enough to qualify as a Retina display, but the last time I speculated about a non-pixel-doubled resolution, it proved to be wildly inaccurate. A 4K display at 27″ is both feasible and technically a “Retina display”, but it’s not doubled in both dimensions. That would make a lot of designers pretty miserable, since they can safely assume today that most Retina displays are used at precisely twice the resolution of their non-Retina counterparts, and therefore don’t have to deal with odd scaling anomalies.