gmic is full-featured open-source framework for digital image
processing,

The framework provides several user interfaces to convert / process
/ visualize generic image datasets, ranging from 1D scalar signals
to 3D+t sequences of multi-spectral volumetric images, hence including
2D color images.

gmic itself is  a command-line tool to use the  image processing
features from a shell.  It may be seen as a "friendly" companion
to the ImageMagick or GraphicsMagick software suites.
