Jakub Steiner wrote an interesting blog about woes of creating resolution independent icons. It's a problem I've been thinking about during the last few days, one that has been solved, at least to some extend, already.
It was solved for fonts. Grid-fitting (aka. "font hinting") is a crucial step on the way to produce legible output at small sizes for any font. Hinting can be manual (e.g TrueType has a stack-based language for it, each glyph in the font contains its own little hint program and as a result of running that program control points for the outlines can be adjusted in any way the creator of the hints desired) or automatic (as used by FreeType). An interesting medium is described in "Example-Based Hinting of TrueType Fonts" paper, in which a method of reusing hints from one font for another are described. All in all it's a very common problem for fonts.
The iSlayer blog that Jakub mentioned makes it very clear we need it fast. His example showing how much worse his logo looks in the vector form than the as bitmap looks almost precisely like the "example of hinting" image that can be found on Wikipedia: (The upper sample in each case is unhinted) When talking about fonts we're just dealing with a subset of our exact problem.
In Qt, Gunnar just implemented support for non-scaling stroke, which is great. Now we need to figure out a way of doing automatic hinting for vector shapes and we'll be set.
I've always been all for manual adjustment of icons on a pixel-by-pixel basis, simply because they looked a lot better, but during the last few days I've became convinced that we can, in fact, create resolution independent icons. Or let me rephrase, not "resolution independent icons" but "icons that preserve their good looks across resolutions". We have the former, we need the latter.
I'm taking a week off and that's exactly what I'll work now.
I think manual hinting is too cumbersome and we'd need a new container format for icons to make it really work. A way of specifying a whole icon theme along hints for each icon to make them look good across different resolutions wouldn't necessarily be a bad idea. In fact that would be great, it's the problem of developing the way of storing and producing those hints that would be quite challenging. XML format (with some namespace of course) that can be embedded right in the SVG's would probably work fairly well but I'm afraid wouldn't be enough. Then there's also a question of how would we get artists to create those hints.
No, I think auto-hinting makes a lot more sense here. The research FreeType people did in that area is outstanding.
All in all, I think I can make it work =)
Oh, and if you have a SVG icon that you hand-adjusted to produce a better looking bitmap, I'd appreciate a lot if you could send me both examples via email to <my first name>@kde.org address so that I have some testcases to work with :)