Making Crisp Retina Icons
What we had been doing was essentially doubling any single-pixel lines from the source image. So if we had an icon with a rectangle bordered by a single pixel, the double-size icon would have a retina bordered by a two-pixel-wide line.
So instead, we had the icons re-done so that the lines were a single pixel in the retina version. But to compensate for the fact that this might not be as bold as the original, we made the line a bit darker (or more opaque, which usually ends up being the same thing).
