> I have read that large vista icons can (but don't have to) use png > compression. I think use of transparency on Vista icons is also supported.
Its true that png offers a compression over bit maps, but I think most people use them as they are associated with partial transparency (ie ability to blend some parts of their color with underlying color). Of course, you can get this with bitmaps too, and in fact for PowerPro pngs are stored in memory as bitmaps. All icons offer full transparency; its the blending that people who use pngs want, I believe. >
