Assume I have an icon on a pure white background in a PNG image. The icon is a solid color, with edges anti-aliased, so they are blended with white. I need to delete the white background so that the non-content is transparent. How can I get the anti-aliased edges to blend from the fill color to transparent, instead of white?
There is a similar question on the site, but this is actually a different case: dealing with solid colors, and anti-aliasing of just the edges, not reblending entire portions of the image. I don't think the answer from the other question applies. I can't reasonably apply a gradient to just the one-pixel edge of an icon. There aren't enough pixels. Also, this method doesn't scale well when the icon edges are irregular (like a Twitter bird).
Perhaps the question is whether it's possible to de-antialias an icon, knowing the foreground and background colors exactly, and to re-antialias it on a transparent background.