darktable is an open source photography workflow application
Swiss army knife of image processing
A collection of packages providing extra functionality for GNU Octave
Astronomical object/structure detection from 1D and 2D data sets.
A small C library for building user interfaces with C, XML and CSS.
Advanced image processing toolbox for Scilab on Unix/Linux/Mac OS
Software for data analysis, image processing, simulations, solver.
Siril is an astronomical image processing software for Linux.