Apple has dubbed the screen on both iPhone 6 models Retina HD, a strange and somewhat redundant label. In reality, the iPhone 6s 4.7-inch display has the same screen density (326 pixels per inch) as the iPhone 5 line. The pixels arent packed any tighter on the iPhone 6there are just more of them, because the screen is 110 pixels wider and 198 pixels taller.
The iPhone 6 Plus is a different story. Its 5.5-inch screen (measured diagonally) has a resolution of 401 pixels per inch, the most ever on an iOS device. That means its a full 1080p displaythe equivalent of a high-definition TV in your (biggest) pocket.
Before we go on, a note about resolutions and scaling, since it can get a little complicated. There are really two ways to measure displays: How big they are (inches) and how many individual dots they can contain (pixels). When we talk about a displays pixels per inch, were describing how small the dots areeffectively, how many of them are packed in any square-inch of a display. These days, most TVs have exactly the same number of dots: 1080 rows and 1920 columns, or roughly 2 million dots. On a 60-inch TV, theyre just less densely distributed than on a 40-inch model. And that same resolution on the iPhone plus is packed into a 5.5-inch spaceits effectively a 5.5-inch HDTV.
In fact, the iPhone 6 Plus so large and so densely packed with pixels that it has actually caused Apple to change the way it handles drawing on its screen. Borrowing a technique Apple used on the MacBook Pro with Retina Display, the iPhone 6 Plus actually renders its interface at 2208 by 1242 pixels. This is a resolution that scales linearly from the displays used on previous iOS devices, which is perfectexcept that the iPhone 6 Pluss screen only measures 1920 by 1080 pixels! So to make the entire image fit, the iPhone 6 Plus reduces the entire interfacescaling it down to 1920 by 1080in order to make it fit on the display.
Scaling displays used to be something that simply wasnt done, because it can create weird artifacts and fuzziness (and requires a lot of graphics power). If youve ever tried to use a non-Retina Mac display at a non-native resolution, you know what Im talking about. But the thing about Retina displays is, the individual pixels are so small that most of the fuzziness is happening on a scale thats just too small to see. The display of the iPhone 6 Plus, like that of the Retina MacBook Pro, looks just finedespite a whole lot of hardware and software working hard behind the scenes to make sure the math adds up.
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