Question

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.

Answer 1

You can use both.

If you want to develop apps to Retina Display (iPhone 4), then you should use image with double resolution (640×960), then, when you create your UIImageView, you divide the size by 2.

CGRect rect = imageView.frame;
rect.size.width /= 2;
rect.size.height /= 2; 
imageView.frame = rect;

Also, you have the option to have a image with @2x on its name, for example [e-mail] (640×960). In this case, you don’t need to divide the size. Using this way:

UIImage * img = [UIImage imageNamed:@"myimage.png"];

Your img var has already divided the size, and if you deploy to iPhone4 it has Retina Display resolution.