This is a 5x5 convolution matrix with a few kernels provided: Sharpen, Box Blur, Gaussian Blur, Edge Detect, and Emboss, intended to be easily to plug into existing materials in order to convolve images as necessary. Provide a step, a UV input, and edit the UV to Color Lookup group (currently just an image). Edit kernels as necessary or use one of the five provided.
There may be better ways to keep node groups linked and unlinked as necessary; I would love to hear about it. This may be more complicated than it need be. Coding support would improve this immeasurably-- matrix, separate, and combine nodes would simplify use-- but I'm not comfortable with Python. I was surprised when I couldn't find something like this already made, and it involves some tedium, so here you go, hope somebody finds it useful.