If the iPad 2 gets a Retina display, what will the resolution have to be? Almost any person who is talking about an iPad 2 strongly believes that it will have a Retina display. Apple had enough trouble quadrupling the number of pixels on the iPhone 4.
Original iPhones: 480 x 320 = 153,600 pixels at 165 PPI
iPhone 4: 960 x 640 = 614,400 pixels at 330 PPI
A writer from GDGT decided to do some math
With a 3.5-inch display, this makes an indescribably huge difference in the legibility and crispness of what’s displayed, and is an otherwise unheard of number of pixels in a screen that size. But in the macro sense, 960 x 640 is not an absolutely mammoth number of pixels for a device to render. This is why the same hardware Apple uses in the iPhone 4 is used in the iPad (at 1024 x 768) and the Apple TV (at 1280 x 720).
Now, the Retina display was so named because Apple found that “there’s a magic number right around 300 pixels per inch that… is the limit of the human retina to differentiate the pixels.”* This assumes holding the device about a foot from your eyes.
Since the pixel density of the iPad wasn’t as great as the original iPhone’s, if you were to keep the screen size the same and simply double the iPad’s resolution it actually wouldn’t get you to Apple’s magic retina number. The iPad at 2x (well, really 4x) would be 2048 x 1536, or 263 PPI.
However, using standard resolution increments, one can still achieve an almost identical PPI to the iPhone 4 on the iPad at a stunning 2560 x 1920 pixels, or the same 330 PPI as in the iPhone 4.
Maybe 2560 x 1920 doesn’t sound like a lot, but it should. Let’s put that in context with the kinds of high resolutions you get on some professional-grade desktop products:
MacBook Pro 15-inch = 1440 x 900
Macbook Pro 15-inch high-res = 1680 x 1050
Macbook Pro 17-inch = 1920 x 1200
Dell 24-inch monitor = 1920 x 1200
Apple 27-inch Cinema Display = 2560 x 1440
I believe that the iPad 2 will not contain a “true” retina display. If they did come out with a higher quality display they might make a 720p display (like the Apple TV 2G) or maybe even a 1080p display. Why Apple calls it a Retina display is because that amount of PPI is the maximum that a human eye can see. So if the called the iPad 2 screen a Retina display that would be very hard for Apple create supporting hardware and still keep the slimness, light weight, and battery life that the current iPad has.