Looking for portable image manipulation library

[Matthias Grimm <matthiasgrimm@xxxxxxxxxxxxxxxxxxxxx>]

Hallo,
to make tile set creation more easy and flexible I need an image
manipulation library. Primarily there are imlib and gdk-pixbuf but
I don't know anything about portablility of those libraries. Imlib needs
Xlibs and gdk-pixbuf needs at least gdk. Which library could I use that
will also be available and easyly compilable under Windows? Any
recommendations? Any other libraries out there? I need image scaling,
alpha blending and format transformations (RGB -> indexed color map).

 Best Regards
   Matthias