All you can do is to get a source image of better quality. Yes, seriously.
Moreover, if this is the photograph, there is nothing better than taking the image of good clarity right in camera. The effectiveness of all those image improvements in post production is highly exaggerated. Only cropping can be nearly perfect.
Your WPF code does not degrade the quality, but you hardly can improve it. If you mean some sophisticated and automated image processing, such as sharpening, I would not recommend doing it.
If you really want to improve images in post-processing, always do it manually using something like Photoshop or other similar software, and only if you are a pretty good master of re-touch. Open-Source GIMP (
http://en.wikipedia.org/wiki/GIMP[
^],
http://www.gimp.org/[
^]) is also a very good thing, in some special aspects even better.
—SA