joetheblow: a GIF has 256 colors, one of which can be used for transparency.
But there two kinds of PNGs: the 256 colors PNGs are like a GIF, maybe a bit better IMO. And there is the 24 bits PNG with an 8 bits alpha channel. It means that, unlike a GIF, the 8 bit alpha channel give you a range of 256 levels of transparency, from a little transparent to completely transparent. Understand?
As for Opera, this is what libpng.org says:
Opera [Opera Software] (Win32, OS/2, BeOS, Mac PPC, Mac OS X, Linux/X, Solaris/X, Symbian OS) - version 3.51 and later; full alpha support in version 6.0 and later (screenshots); broken binary transparency in older versions (apparently only for palette-based images, where the alpha value of the first palette entry is misinterpreted as the index of the palette entry to be made fully transparent, a la GIF); progressive display (except transparent PNGs on Windows versions); full gamma support (assumes a file gamma of 1/2.0 for unlabelled PNGs, vs. 1/2.2 for GIFs and JPEGs); bogus ``out of place IHDR'' errors and segfaults in Linux version 4.x or 5.x; read-only; adware/commercial. (Version 3.50 supported PNG only via old-style plug-ins, such as PNG Live 1.0, that supported neither transparency nor progressive display; see Netscape Navigator above. Version 3 and possibly 4 also supported Windows 3.x, but that support was dropped from more recent versions.)
For information on all the browser supports of PNG, go at http://www.libpng.org/pub/png/pngapbr.html
Of course they say IE doesn't support transparent PNG, I bet they don't know the secret trick.
