In 1x place image with resolution 320 x 480.

In 2x place image with resolution 640 x 960.

In Retina 4 2x place image with resolution 640 x 1136.

in 3x place image with resolution 1242 x 2208.

Images of Retina 4 2x will upscale to resolution 750 x 1334.

Images 3x will downscale to resolution 1080 x 1920.

http://stackoverflow.com/questions/26020979/xcode-6-xcassets-for-universal-image-support

##Size Class for launch image

• 2x [- +] for iPhone6
• 2x [- +] for iPhone4
• 3x [- +] for iPhone6plus
• Retina 4 2x [- +] for iPhone5