I'm currently learning about convolutional neuronal networks (CNN) and have implemented a basic convolution operation for the matrices in my C++ library FlexLib2.
The implementation is still experimental, since I need to implement some test cases. Hopefully after the Gamma 2016 conference in Heidelberg I find some time for doing so 🙂
By the way: Gimp has the ability of manipulating a picture using a used defined convolution matrix. Very cool!