Firlefanz, to answer your question in your forum about how to process all your 600 files with pngout, open a command prompt, cd to the directory containing your PNGs, and type this command

for %I in (*.png) do pngout.exe %I

Either have pngout.exe in your PATH, in the same directory as the PNGs, or specify the full path to it, such as

for %I in (*.png) do c:\utils\pngout.exe %I