Gruber has a short article that references a longer article on why the iPhone uses regular (gray-scale) anti-aliasing instead of the clever sub-pixel method used by OS X. He concludes that the pixel density is high enough that regular is good enough.

But there is a very simple reason that sub-pixel is not used on the iPhone: screen rotation. Sub-pixel anti-aliasing relies on the increased spacial density in the horizontal direction of the individual color bars (and on the pathetic color-resolution of eyes). Once you switch vertical and horizontal by rotating the screen, this no longer works and you have no option but to have a high-enough pixel resolution to make simple anti-aliasing work well. It also helps that sub-pixel anti-aliasing takes a lot more computation than simple, and you want to minimize that in a portable device.

The 160 dpi used on the iPhone is probably about the minimum you can get away with. The current 100 dpi of Cinema displays is about a factor of 2 better (100 * 3 = 300, just about 2 * 160 = 320) than the iPhone. And in Leopard in the places where sub-pixel anti-aliasing is not used, you can see the difference in the way the text looks and it is irritating.

Tags: Gruber, iPhone, Anti-Aliasing