I have made some experiments with Blender compositor functionality by adding a new node exposing G’MIC image processing functionality. It is most useful with NPR rendering, but it can be used in other ways too. I grew tired of manually processing, depth merging and combining the image layers in Gimp with a bunch of clumsy helper scripts. Version 0.2.0 now also supports many popular G’MIC GIMP extension filters.
Here is the source code repo with a link to a binary release (Windows 64 bit)
No Linux or Mac builds yet. The binaries built with Visual Studio 2017 and it should be a drop-in replacement for Blender 2.79. Still, it is experimental so take backups of your work just in case. If you test it let me know if it worked on your machine or if you had any problems. If you get a missing .dll error, try installing Visual Studio 2017 Redistibutable.
Some other ramblings:
I’m also investigation the possibly of adding a GLSL image processing node (might be very tricky because of the OpenGL context and threading). It could make possible to use filters from Shadertoy etc. Is there any interest in these kind of additions or can anyone suggest something similar that would be more useful to people? I tried googling around, but I couldn’t find if anyone has already done something like that.
One other idea I have been playing in my head with is to make a Python compositor node (a bit like OSL node in Cycles). RGBA data is passed to user defined Python code as a Numpy array and the code can modify the data or pass it to external programs/libraries and back without a need to recompile Blender. Could be very slow in worst cases, but for simple things it might be fast enough. I would need to investigate how the Python GIL etc. interacts with the compositor node threading…