Check this out :
This is something that I wrote for AfterStep window manager,
but it has grown to be rather powerfull raster image
manipulation library. The accent has been made on high quality
image processing - instead of 8bit per channel with saturation,
it does 32 bit per channel with subsequent translation into 8bit
with error diffusion to compensate for bandwidth loss. Image
data could then be compressed using RLE on per channel basis. It
actually performs very well, despite perceived complexity.
Some other things to mention :
Supports about 10 file formats.
Could work with and without X windows.
XML based image manipulation.
High quality 128bit raster engine.
15 image blending methods.
Fast image scaling with interpolation.
Gradients and TrueType antialiased text rendering.
In memory image compression.