Saving NSImage for use as iOS/macOS icons

I have a simple app I wrote to take a large image and reduce it into the popular/required sizes for iOS and macOS icons in @1x, @2x and @3x sizes.
This creates images with the correct sizes… but they are all 72dpi

Does that matter? or is @2x supposed to be 144dpi, and @3x 216dpi?

If so, anyone know how to set/convert the dpi of an existing NSImage?

they should all be 72 DPI with different sizes