iPhone 4和iPod Touch 4有一个新的特性：在屏幕尺寸不变的前提下，分辨率提升一倍（320 x 480 => 640 x 960）。苹果将这个特性命名为Retina。
用苹果的话讲：
Retina显示屏的超高像素密度已超过人眼能分辨的范围。
Retina对图像设计（图标、启动画面和其它所有像素有关的东西）有什么影响呢？如果我们的app要支持Retina，就要提供高分辨率的（宽x2，高x2）的图片。同时，为了支持没有Retina的设备，仍旧要准备低分辨率的版本。换言之，我们要准备两套图。
针对不同分辨率的图片，苹果规定了一个命名规范：假如一个普通分辨率的图片，文件名是“abc.png”，那么与其对应的高分辨率的文件名就应该是“abc@2x.png”，多了“@2x”。
举一个例子：
Icon.png
Icon@2x.png
这里需要注意的是，虽然在浏览器中，第二张图片的面积是第一张的4倍，但是在支持Retina的iPhone中，显示的大小是一样的。
格式和尺寸
图标和启动画面的格式：推荐使用PNG格式，可以是标准的24位颜色（红、绿和蓝各用8位），外加alpha通道的8位。不要在app图标上使用透明色。
图标的尺寸：苹果有一份完整的文档，列出了app所需的全部图标尺寸，和其各自的使用环境。
Technical Q&A QA1686: App Icons on iPad and iPhone
http://developer.apple.com/library/ios/
iPhone-only Apps
Include the following in your application’s Resources group in the Xcode project:
Table 1 iPhone-only apps icon requirements.
| Image Size (px) | File Name | Used For | Required Status |
| 512×512 | iTunesArtwork | Ad Hoc iTunes | Optional but recommended |
| 57×57 | Icon.png | App Store and Home screen on iPhone/iPod touch | Required |
| 114×114 | Icon@2x.png | Home screen for iPhone 4 High Resolution | Optional but recommended |
| 72×72 | Icon-72.png | Home screen for iPad compatibility | Optional but recommended |
| 29×29 | Icon-Small.png | Spotlight and Settings | Optional but recommended |
| 50×50 | Icon-Small-50.png | Spotlight for iPad compatibility | Recommended if you have a Settings bundle, otherwise optional but recommended |
| 58×58 | Icon-Small@2x.png | Spotlight and Settings for iPhone 4 High Resolution | Recommended if you have a Settings bundle, otherwise optional but recommended |
iPad-only Apps
Include the following in your application’s Resources group in the Xcode project:
Table 2 iPad-only apps icon requirements.
| Image Size (px) | File Name | Used For | Required Status |
| 512×512 | iTunesArtwork | Ad Hoc iTunes | Optional but recommended |
| 72×72 | Icon-72.png | App Store and Home screen on iPad | Required |
| 50×50 | Icon-Small-50.png | Spotlight on iPad | Optional but recommended |
| 29×29 | Icon-Small.png | Settings on iPad | Recommended if you have a Settings bundle, otherwise optional but recommended |
Universal Apps
Include the following in your application’s Resources group in the Xcode project:
Table 3 Universal apps icon requirements.
| Image Size (px) | File Name | Used For | Required Status |
| 512×512 | iTunesArtwork | Ad Hoc iTunes | Optional but recommended |
| 57×57 | Icon.png | App Store and the Home screen on iPhone/iPod touch | Required |
| 114×114 | Icon@2x.png | Home screen for iPhone 4 High Resolution | Optional but recommended |
| 72×72 | Icon-72.png | App Store and Home screen on iPad | Required |
| 50×50 | Icon-Small-50.png | Spotlight on iPad | Optional but recommended |
| 29×29 | Icon-Small.png | Settings on iPad and iPhone, and Spotlight on iPhone | Recommended if you have a Settings bundle, otherwise optional but recommended |
| 58×58 | Icon-Small@2x.png | Spotlight and Settings for iPhone 4 High Resolution | Recommended if you have a Settings bundle, otherwise optional but recommended |
http://uedc.163.com/5294.html
上传到App Store需要512px X 512px的图片
在iPhone 960px X 640px分辨率中
图标显示尺寸 114px X 114px
20像素的圆角
4像素的90度黑色投影
2像素的90度白色内投影
默认自带的高光
在iPhone 480px X 320px分辨率中
图标显示尺寸 57px X 57px
10像素的圆角
2像素的90度黑色投影
1像素的90度白色内投影
默认自带的高光
在iPad 1024px X 768px分辨率中
图标显示尺寸 72px X 72px
13像素的圆角
2像素的90度黑色投影
1像素的90度白色内投影
默认自带的高光
iTunes Artwork icon ───────── 512px (90px)
App icon(iPhone4) ──────────114px (20px)
App icon(iPad) ────────────72px (12px)
App icon(iPhone 3G/3GS) ───────57px(10px)
Spotlight/Settings icon icon(iPhone4) ── 58px (10px)
Spotlight/Settings icon icon(iPhone 3G/3GS/iPad) ──── 29px (9px)
使用现有的iOS图标模版
App Icon Template by Michael Flarup
http://www.pixelresort.com/blog/app-icon-template
http://appicontemplate.com/ (最近更新, 包括iPad Retina)
最流行也是最强大的，里面包含很多常用的材质。
iOS icon template for Illustrator CS5 by Jon Hicks
http://hicksdesign.co.uk/journal/ios-icon-template-for-illustrator-cs5
Ai的模板来自firefox的logo设计师
iOS App Icon Template by Louie Mantia
http://dribbble.com/shots/461654-iOS-App-Icon-Template
其他不是太流行的模板文件:
http://blog.cocoia.com/2010/iphone-ipad-icon-psd-template
http://blog.cocoia.com/2010/iphone-4-icon-psd-file/
http://dribbble.com/shots/446198-Freebie-iOS-icons
http://dribbble.com/shots/473390-iOS-App-Icons-PSD-Template
http://dribbble.com/shots/271363-iOs-icon-Free-PSD
http://dribbble.com/shots/37493-Icon-Template
http://dribbble.com/shots/292559-Icon-Template
http://dribbble.com/shots/44805-iOS-Icon-Template
参考：http://www.uimaker.com/uimakerhtml/uistudy/2012/0424/34102.html
