Ahead-of-time Resolution Independence
The best quality results — and the method Apple chose for the iPhone 3GS
to iPhone 4 transition — comes from pre-rendered images, built for specific
devices, at specific resolutions: bespoke designs for each required size, if
you will. It’s more work, but pre-rendering images ensures everything
always looks as good as possible.
Apple chose to exactly double the resolution from the iPhone 3GS to the
iPhone 4, making scaling even easier (different from the approach
of Google and Microsoft — notice that this article is not relevant to the
latest version of Microsoft’s mobile OS — proving yet again that controlling
the entire stack has huge advantages).