I can only speak for my own nodes, but if you are on a M1 mac, they might not have been recompiled to support it. If you downloaded my nodes yesterday they should work in theory, but you might have to double-click the .vuonode to install them.
Oh, I'm answering before reading now it seems 😅. Then you want the "Mask Image by Brightness" node I think. Alternatively a custom shader that converts a luma range in the input image to alpha.
There aren't any examples in it yet, but it should get you going with the barebones needed to drop in an example file from the node examples by team Vuo, and add it to the CMakelists file for compilation.
I would actually rather recommend "The nature of code" by Daniel Schiffman found here: https://natureofcode.com/. This explains more the realm of graphics programming and concepts for creative coding. It is made for Processing, but as the Vuo API deals with most of the heavy C stuff for simpler nodes, it isn't too far off for making nodes if you can manage to translate for instance a vec3() to a VuoPoint3d().
