Physical pixels are the smallest particles that actually exist, and can become the resolution.
Computer 1 development px = 1 physical pixel,
but
iphone8 1px = 2 physical pixels
iphone6 Plus 1px = 3 physical pixels
That is to say, the clarity of a picture seen on the computer and the phone will be different.
If it is a 1px = 2 physical pixels,
that is to say, the prepared picture needs to be twice as much as that required by the phone, and then manually double it, you can Make pictures on mobile more clear
You can use the cutterman's multiple cuts of the ps software to quickly generate the ratio required by the mobile phone
