[l2h] Re: Problems in PNG generation

Marek Rouchal Marek Rouchal <marek@btfmd1.fs.uni-bayreuth.de>
Tue, 21 Sep 1999 09:25:52 +0200 (CEST)

On Tue, 21 Sep 1999, Ross Moore wrote:

> > The new problem is that the PNG has a gray background, while the GIF is
> > transparent. Of course I use the same pstoimg routine, just changing the
> > configuration file (99.2 revision 1.29)
> > 
> > ==> Is that grey background with PNG a bug, or a "feature"?
> The fact that it is grey is a "feature".
> That fact that it is not also transparent is either a "bug"
> or a configuration error. I don't know which, sorry.

It is definitely a bug in Netscape: The PNG is created "transparent", but
there is -- AFAIK -- currently no browser that is capable of displaying
the transparency (so-called alpha-channel) of PNGs correctly. Does anyone
know about a browser that does not have this problem?

> There is (usually)  no such problem with .gif images, as there are
> reliable routines to determine which color is the background,
> in order to set it to be transparent.

The algorithm is supposed to be the same for ppmtogif and pnmtopng. The
problem is that bowsers display the gray background color instead of
recognizing that it should be 100% transparent.

Nothing we can do about that at the moment... :-(