iOS 屏幕尺寸、逻辑分辨率、物理分辨率之间的相互关系

|型号| 屏幕尺 寸（inch) | 逻辑分辨率（point）| 缩放因子（scale factor）|物理分辨率（pixel）|像素 密度（PPI）|
|---|:---:|---||
|iPhone3GS |3.5 |320480| @1x|320480|163|
|iPhone4/4s|3.5|320480| @2x|640960|326|
|iPhone5/5s|4|320568| @2x|6401136|326|
|iPhone6/6s/7|4.7|375667| @2x|7501334|326|
|iPhone6Plus/6sPlus/7Plus|5.5|414736| @3x|12422208|401|

 点（point）和像素（pixel）换算关系

iPhone3GS：
1point = 1pixel
**iPone4/4s、iPhone5/iPhone5s、iPhone6/iPhone6s、iPhone7: **
1point = 2pixel
iPhone6Plus/iPhone6s Plus、iPhone7 Plus:
1point = 3pixel