ImageMagick 7
darktable is an open source photography workflow application
A fast image processing library with low memory needs
Library to encode and decode images in WebP format
Swiss army knife of image processing
Lynkeos is an astronomical webcam image processing software for OS X.
A collection of packages providing extra functionality for GNU Octave
Astronomical object/structure detection from 1D and 2D data sets.
ProStack - a platform for image processing and analysis
Image processing library in C/C++
Resilient Image Library - successor to DevIL
Easy converting PNM to (MASK+FG+BG)-pdf.
Tools to access streams in PDF-files at the object level.
Easy converting pgm and ppm to (MASK+FG+BG)-djvu.
Collection GIMP plugins by zvezdochiot
Improved JPEG encoder
Libraries and command line tools for medical image processing.
Graphic Live Mixer
Digital image processing programs for Windows and Linux systems.
Some image processing tools
A small C library for building user interfaces with C, XML and CSS.