[willyt]

App icons in OS X are interpolated between about 4 different sized images. I remember reading about this in the developer docs back in about 2002. I'd be surprised if Apple don't have pretty much the same patent on this already but registered 10 years earlier :-)

[dmdeller]

Mac OS has done this since much earlier. The classic Mac OS needed at least two different representations of the same icon, one for the desktop (32x32) and one for the application switcher (16x16). The application switcher, initially called MultiFinder, was introduced in 1987[1]. If memory serves, the various sizes of an icon were stored together in the ICNS resource of the app binary's resource fork. There was a developer tool provided by Apple called ResEdit which allowed you to view or change the icons of any application, in a nice GUI editor (of course).

[1]: https://en.wikipedia.org/wiki/Multifinder