I read from http://www.apple.com/iphone/specs.html that IPhone4's screen is 960-by-640-pixel resolution at 326 ppi.
But in Xcode's IPhone4.3 simulator, when I manipulate the display objects, print the [UIScreen mainScreen].applicationFrame, it is 320*480.
So if I wanna use a picture as the main screen's background of my app, which size I should use? 640*960 or 320*480?
Or Which kind of images should I use ? The size of images can affect the details a lot.