This is more an effect than a brush per say, but here is a way to posterize an image:
You can choose how much steps you want and specify a value range to better adapt to the image (a dark image will need a range focused on smaller values for exemple).
The effect is not as good as what you could find on a software with a dedicated effect system, but I think it's still useful (for value studies for exemple).
Here is the file: https://github.com/KevinBockelandt/blac ... ze.bkbrush
Hope you find it useful!
