G'MIC is a full-featured open-source framework for image processing. It provides several different user interfaces to convert/manipulate/filter/visualize generic image datasets, ranging from 1d scalar signals to 3d+t sequences of multi-spectral volumetric images, thus including 2d color images.
Invoke the interpreter by typing 'gmic'. Follow this with a series of items, separated by white space. The items are generally G'MIC commands followed by their affiliated parameters. Some commands do not have parameters, so G'MIC relies on a leading hyphen to distinguish commands from other items on the command line.
Parameters consist of numbers, letters or words separated by commas, usually with no intervening white space. Occasionally, a parameter will embed white space; these need to be quoted.