Devices in Device Specific image set in asset catalog

ios xcode iphone-6 iphone-6-plus asset-catalog

1x: no need
2x: 3.5', 4' and 4.7' — see below for 4'
3x: 5.5'
Retina 4 2x: 4' if image ratio is different from 3.5', i.e. image have the same width but different height