The resolution of pictures of IOS app

Question

My current resolution of all the pictures (all of png format) in my app is 300, which I realized is too high,

I heard that 72 ppi will be enough, but however I just wanna make the best vision effect of these pictures,

so what is the best resolution of pictures for IOS app? both Retina and former screens.

And one more question, I tried to save my pictures in photoShop to 72 ppi,

but after I drag that picture to my XCode project, XCode tells that the resolution is 71 pixels/inch,

would it be a problem?

THanks a lot!

Answer 1

The answers to your questions can be found here.

But in short, 72 dpi is what you want. Retina screen imagery is termed 'High Definition' but is simply twice the size as non Retina imagery, i.e. your app icon is nominally 57x57 pixels but your retina variant of the same icon is 114x114 pixels (both images being 72dpi).

Re: your photoshop query. I have no idea about photoshop itself but in this instance I can't imagine why an image less than 72dpi would cause too great an issue. Photoshop gurus will be able to tell you why this is happening.