ios retina

note:

I just create test app and test.
So for devices with out retina:
ImageName.png - For iPhone/iPod
ImageName~ipad.png -- For iPad
For devices with retina display:
ImageName@2x~ipad.png -- For iPad
ImageName@2x.png - For iPhone/iPod
And you can still use @2x if you iPhone high resolution image and iPad high resolution image have the same size.
To load image just use [UIImage imageNamed:@"image.png"];