参考http://blog.csdn.net/complex_ok/article/details/6061188和http://www.cocoachina.com/bbs/read.php?tid-17132.html

iOS设备现在有三种不同的分辨率：

iPhone 320x480,

iPhone 4 640x960,

iphone 5 640* 1136

iPad 768x1024。

以前程序的启动画面(图片)只要准备一个Default.png就可以了，但是现在变得复杂多了。

如果一个程序，既支持iPhone又支持iPad，那么它需要包含下面几个图片：

Default-Portrait.png iPad专用竖向启动画面 768x1024或者768x1004

Default-Landscape.png iPad专用横向启动画面 1024x768或者1024x748

Default-PortraitUpsideDown.png iPad专用竖向启动画面(Home按钮在屏幕上面)，可省略 768x1024或者768x1004

Default-LandscapeLeft.png iPad专用横向启动画面，可省略 1024x768或者1024x748

Default-LandscapeRight.png iPad专用横向启动画面，可省略 1024x768或者1024x748

Default.png iPhone默认启动图片，320x480或者320x480

Default@2x.png iPhone4启动图片640x960或者640x920

Default-568h@2x.png iphone5 启动图片 640*1136

为了，指定特定的图片为启动画面，还可以在Info.plist中添加UILaunchImageFile，解释如下所示：

UILaunchImageFile (String - iPhone OS) specifies the name of the launch image file for the application. If this key is not specified, the system assumes a name of Default.png. This key is typically used by universal applications when different sets of launch images are needed for iPad versus iPhone or iPod touch devices.

If you include this key in your Info.plist file, any launch images you include in your application’s bundle should be based on the string. For example, suppose you want to include portrait and landscape launch images for iPad using the base name MyiPadImage.png. You would include the UILaunchImageFile~ipad key in your Info.plist file and set its value to MyiPadImage.png. You would then include a MyiPadImage-Portrait.png file and a MyiPadImage-Landscape.png file in your bundle to specify the corresponding launch images.