例如:Iphone6的PPI计算:
c=4.7*2.54=11.938cm c边像素=1530.378pcs
c边每个像素长度=0.007801cm a=1334*0.007801=10.40653cm b=750*0.007801=5.85075cm
PPI=1334/10.40653*2.54 or 750/5.85*2.54=326
a
b
c
750/5.85*2.54=326ppi