G'MIC is an open and full-featured framework for image processing in Gimp.

You have several different user interfaces included in G'MIC that will convert/manipulate/filter/visualize generic image datasets, from 1d scalar signals to 3d+t sequences of multi-spectral volumetric images.

G'MIC Features:

A portable and thread-safe C++ library 'libgmic' for generic image processing, embeddable in third-party applications.
A command line interface 'gmic' to perform image processing operations from a shell.
An easy-to-use plug-in 'gmic_gimp' which adds hundred of new filters to GIMP
A web-service 'G'MIC Online', to apply image fiters directly on a web-browser.
A Qt-based interface 'Zart' for real-time manipulation of webcam images.
A complete script language to develop your own complex image processing pipelines.