The science of Retina displays

The march began in 2010 with the iPhone 4, gathered pace in 2012 with the third-generation iPad, and reached its dramatic peak last month with the launch of a new breed of MacBook Pro. As Apple adds its stunning Retina displays to ever-larger devices, resolutions climb higher, and the sharpness continues to appeal to an audience long fed on scraps by manufacturers.

How we’ve ended up in such a situation is a question many have been asking for some time. Have higher-resolution laptop displays been an insurmountable manufacturing issue, or is it the software that’s held us back? Could these sharper screens have been here years ago if manufacturers had only invested as they are – or, at least, Apple is – seemingly doing now?

In this feature, we look at how the field of display technology is taking leaps forward, largely – but not exclusively – driven by a single company. You’ll learn how Apple has managed to deliver panels at higher resolutions than its competition, how operating systems are making it all work, and whether the future is one of Retina-quality displays on every device.

The numbers behind Retina

The MacBook Pro’s Retina display looks almost paper-like, and that’s down to two key design factors. First, it’s glossy, but without the usual feel of looking at a reflective pane of glass. This is because it’s constructed in a different way to standard LCD panels. As the teardown experts at iFixit explain: “Rather than sandwich an LCD panel between a back case and a front glass, Apple used the aluminium case itself as the frame for the LCD panel and used the LCD as the front glass. The entire display assembly is an LCD panel.” That’s why the panel is so thin, allowing Apple to trim down the MacBook Pro.

In most laptop displays, that would be the most interesting fact, but few could argue that’s the chief selling point of the MacBook Pro: the more important factor is pixel density. If you know the resolution and size of a screen, you can calculate the number of pixels per inch (ppi) it has, where a higher density makes each pixel finer and the overall image sharper.

In Apple’s own words, on a Retina display the “pixel density is so high your eyes can’t discern individual pixels”. If that statement sounds vague, that’s because it isn’t as simple as having a golden number to aim for. As screens become larger, so too does the distance from which they tend to be viewed; to have the same perceived sharpness, a smartphone in the hand must have a higher pixel density than a laptop on a desk.

During Apple’s 2010 unveiling of the first Retina display on the iPhone 4, Steve Jobs announced a loose figure for smartphones. “There’s a magic number right around 300ppi,” he said, “that when you hold something around 10 to 12in away from your eyes is the limit of the human retina to differentiate the pixels.” There was disagreement at the time about the claim, since it falls some way short of the resolve of perfect vision – but few people have perfect vision. Instead, 300ppi is safely beyond the 286ppi capability of 20/20 vision from that distance, so for most people Jobs was right: the individual pixels are indiscernible.

In fact, the iPhone 4 and 4S have a 326ppi display, the latest iPad is 264ppi and the new MacBook Pro is 220ppi, all of which – given the variations in viewing distance – meet Jobs’ apparent requirement of invisible pixels with 20/20 vision. By contrast, a 15.4in laptop display with today’s most common 1,366 x 768 resolution has a density of 102ppi; even at 1,920 x 1,080, it’s still only at 143ppi. It’s possible to buy a 13.3in laptop at that resolution to give a better 166ppi, but it’s a rare option offered by a select few manufacturers.