To put it into number, the iPhone 3 comes with a 3.5 inches screen and a screen resolution of 480 x 320. That is equivalent to 163 pixels per inch (ppi). For the iPhone 4 and 4S, with the same 3.5 inches screen, the screen resolution is now 960 x 640 ( 326ppi), double that of its predecessor. As for the new iPad, the resolution is 2048 x 1536 on a 9.7 inches screen, equivalent to 264 ppi. Why does this matter? Anything that is printed digitally or being displayed on a screen is being done so with pixels, tiny squares that when grouped together form images and characters. The more pixels that are in any given area determines how clear the image is, and from what distance the pixels can be seen with the naked eye. The goal of Retina Display is to make it so that the pixels cannot be seen with the naked eye (using two screen pixels to represent one actual pixel, thus making each pixel too small to be noticeable). To accomplish this, Apple first came up with their assertion that the maximum amount a human retina can see is 300 pixels per inch from a distance of 12 inches, or 57 arcseconds per pixel.
This assertion was disputed by Raymond Soneira, president of DisplayMate Technologies, who believes the human retina can see 477 pixels per inch. This assertion was in turn disputed by the author of Bad Astronomy, Phil Plait, whose has collaborated with NASA on the Hubble Space Telescope camera. He believes that 300 pixels per inch will not be seen with a person who has 20/20 eyesight, and that only people with eyesight better than that would see the individual pixels. Going on the assumption that an iPhone or iTouch will be viewed at a distance of approximately 12 inches, Apple made this 960 x 640 display (measured in pixels) 326 pixels per inch, just over the amount that the eye should be able to detect. This means the naked eye shouldn’t ever see those pixels, and should only see smooth text and images. Apple then brought that same Retina Display technology to their iPad. With a larger screen, 9.7 inches, it requires more resolution. They have made the resolution 2048 x 1536, which is even better than a standard HDTV display, a million more in fact, just to put it in perspective.
Bear in mind, though, that this resolution is going to depend on how it was originally uploaded. Take pictures on Facebook. If your friends upload bad, fuzzy pictures with a very low pixels per inch to Facebook, when you view them with your device that has Retina Display, it’s not going to look any better. You can’t fix what’s already there. But if your friends upload pictures that have a high pixels per inch, you will see them as intended. Going back to the question if Retina Display is something we need, it all depends on personal preference. Some people didn’t need to update to CD players, because they were happy listening to their music on cassette tapes. Similarly, some people won’t mind a lower pixel per inch display. It’s not a necessity. However, if you’re wowed by great displays, you will enjoy every single pixel, whether you can see them or not.
