默認情況下ios是用4個點表示一個實際的像素點，4：1的關係，所以圖像在ios設備上運行時，看上去要比實際用像素畫的比較大。
文檔裏是這麼說的。稍後追加
The different resolutions only come into play if you want to use high res mode on the retina displays (iPhone 4, iPod Touch 4th Gen).
If you enable high res mode, then you can/should use the larger textures for your map.
If you don't, then the retina display will use the same resolution as the earlier models. (It uses 4 pixels of the display to display 1 "normal" pixel, so it works out to the same layout as "old" devices)
See Also:
http://www.cocos2d-iphone.org/forum/topic/8511
http://www.cocos2d-iphone.org/forum/topic/9315