megaimage is an image manipulation extension for Tcl. It's written in C and supports RGBA buffers, antialiased line drawing, blending of megaimage objects, blending with arbitrary lines and rows, manipulation of pixels as lists...
License: BSD
Platforms supported: Unix, Mac, Windows.
Download: See megapkg
The documentation is available here:
http://www.xmission.com/~georgeps/implementation/software/megapkg/megaimage.html