[Cialug] C code for conversion between PPM and PNG files

[Morris Dovey]

I've been modeling behavior of directly solar-powered (non-electrical)
engines and wrote some C code to allow me to "plot" into a graphics
file. I've put one of my test programs and a couple of sample plots at

   http://www.iedu.com/DeSoto/Misc/Plot/

so you can have some context. The initial code seems to be working, but
(for simplicity) I'm creating PPM files that I pull into a graphics
editor and save as PNG files.

What I'd like is _minimal_ standard-conforming (for portability) C code
to convert PPM files to PNG and vice versa that I can share freely with
R&D teams working on the same project around the world to make it easier
for them to share and publish their findings.

I've searched without found anything suitable - and before I jump off
the deep end to re-invent this wheel, I thought I'd see if anyone here
has (or is aware of) a solution.

Morris Dovey
http://www.iedu.com/DeSoto/