G’MIC is an open source framework for image processing and manipuation, which came to my attention with it’s recent integration into Krita 5. G’MIC, or GrayC’s Magic for Image Computing is available in a number of different forms, from a very ImageMagick-esque command line interface, to an online version, as well as plugins for several popular graphics applications including GIMP, Photoshop, Krita, Paint.NET and more and finally as a C++ library for integration into your own applications. The entire G’MIC project is open source and hosted on GitHub and is updated frequently.
G’MIC comes with it’s own scripting language (tutorial here) which is used to create all of the 400+ filters included in G’MIC and enables you to quickly create your own.
G’MIC is described as:
G’MIC is a full-featured open-source framework for digital image processing, distributed under the CeCILL free software licenses (LGPL-like and/or GPL-compatible). 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, hence including 2d color images.
You can see G’MIC in action (online, in Krita and Affinity Photo) in the video below.