iPhone屏幕分辨率和屏幕点之间的关系
1x：3.5英寸普通屏 设备: iPhone4之前的iPhone 320*480pixel320*480pt
2x：3.5英寸Retina显示屏 设备有 iPhone4和iPhone4s640*960pixel320*480pt
R4：4.0英寸Retina显示屏 设备：iPhone5，iPhone5c，iPhone5s640*1136pixel320*568pt
| 1x | 3.5英寸普通屏 | 设备: iPhone4之前的iPhone | 320*480pixel | 320*480pt |
| 2x | 3.5英寸Retina显示屏 | iPhone4和iPhone4s | 640*960pixel |
320*480pt |
| R4 | 4.0英寸Retina显示屏 | iPhone5，iPhone5c，iPhone5s | 640*1136pixel | 320*568pt |
default.png: 3.5英寸普通屏设备，默认可以使用[UIImage imageNamed:@"default"]
[email protected]: 3.5英寸Retina屏设备调用[UIImage imageNamed:@"default"]会使用这张图片
[email protected] 4.0英寸Retina屏设备调用[UIImage imageNamed:@"default"]会使用这张图片
不同屏幕设备可以根据名字动态使用不同分辨率的图片。
App icon
1x·········iOS5，6 spotlight-IOS5-7setting ·············58*58
2x·········iOS7 Spotlight········································80*80
2x·········IOS7 APP···········································120*120
LaunchImage
1x·········320*480
2x·········640*960
R4·········640*1136