Thanks for the hint.
I experiment with Alias, feather, Gaus-blur and contrast.
For contrast I have used MS Photoeditor because the contrast function from Paint.net has not done what I had expected :-)
I don't know exactly how I got it but I think the result is useable.
EDIT: For explanation I want to produce very fine copies from my credentials for application documents. I'm not very practised with grafic prgrams.