[mrtg] Why gif instead of png?

[Fred Zwarts (KVI)]

We use mrtg for many years now. In the beginning it produced .gif pictures, 
but already for many years it produces .png pictures. Yesterday we upgraded 
our system. We now use a Suse system (SLES 11 with the latest updates) which 
had gd 2.0.36 installed and gd-devel-2.0.36. We downloaded and installed 
mrtg 2.17.2. Now mrtg produces .gif pictures again. We want to stay with 
.png, because the pictures are also used in other html pages. I cannot find 
a configuration option to produce .png files again. How can this be solved?

Fred.Zwarts.