Rimlight - Convolution matricies for angle based edge detection
Download the tool here or on Nukepedia
I’ve recently made this rimlight gizmo after spending some time looking into convolution and colour matricies to get a better understanding of them. The gizmo is based on Andrea Geremia’s Edge Rimlight tool and in a similar fashion works by using a 3x3 convolution matrix with a Prewitt filter. It essentially does an edge detect but isolates the edges facing into a certain direction specified by an angle slider.
Some of the key differences to Andrea’s gizmo are that I wanted to make it possible to smoothly adjust the angle of the rim so it is animatable as well as add some edge extension and image based edge distortion features to get a more natural/less uniform result. The gizmo works especially well if you have hard roto for the thing you want to apply a rim to and in general on clothing or high contrast plates. It’s best suited for creating these strong/harsh rim lights on characters or objects but I’ve also used it in the past to drive an energy distortion effect around an object.
It’s one of those tools that adresses quite a niche problem but when you are in a situation where you need something like it, it can be super useful. Below you can see two very quick and dirty examples where I’ve pulled a rough key to get a usable alpha of the person and then used the RimLight gizmo to get the rim light.
Effect on plate (top), Alpha generated by the rimlight gizmo (bottom)