Does anyone have suggestions or links to papers on how to implement a watercolor filter as a post process effect? For example, for those that have the book "Real-Time Rendering 3rd edition" I am looking for something like Figure 10.23 (page 473), but it doesn't elaborate much. Is the "Gaussian difference" just a Gaussian blur, but where it won't blur over edges? What is a good edge detection algorithm to use to produce the lower-left image?