Pixopedia XE (Extended Edition) is a portable image editor with a powerful and configurable brush engine. Its auto-brushing tool allows for the emulation of various photographic painting styles. Advanced image filters and processing is also supported through IPP, OpenCV and even neural network style transfer via its integrated Lua scripting engine.
Pixopedia XE is not for the faint-of-heart and has a steep learning curve. However, it is very powerful and should be very rewarding for those who take the time to master it.