iphone各个设备的分辨率和对应的像素尺寸 以及所用到的 在Images.xcassets中的图片规格
iPhone 4S
Screen Size: 3.5 Inches
Resolution: 640 x 960 (Half: 320 x 480)
iPhone 5
Screen Size: 4.0 Inches
Resolution: 640 × 1136 (Half: 320 x 568)
iPhone 5S/5C
Screen Size: 4.0 Inches
Resolution: 640 x 1136 (Half: 320 x 568)
iPhone 6
Screen Size: 4.7 Inches
Resolution: 828 x 1472 (Half: 414 x 736)
Resolution: 750 x 1334 (Half: 375 x 667)
iPhone 6 Plus
Screen Size: 5.5 Inches
Resolution: 906 x 1704 (Half: 453 x 852)
Resolution: 1242 x 2208 (1/3: 414 x 736)
The size ofiPhone 6 Plus is @3x scaling. So, it is divided by 3.
