Professional Digital Compositing: Essential Tools and Techniques

Chapter 6. Convolution Filters

"Know the math behind what you are doing. A over B-What does that mean? You have to know the procedure-you have to know why."

——Johnathan R. Banta, lead compositor, Zoic Studios, Culver City, California

Filters, in the form of effects and nodes, are an integral part of compositing. Many common filters, such as blur and sharpen, are based on a convolution kernel. Such kernels, which are detailed in this chapter, are equally capable of creating stylized effects, such as emboss and edge enhance. After Effects and Nuke provide a long list of convolution-style filters. Nuke offers Convolve and Matrix nodes that allow you to design your own custom convolutions. Hence, it's important to understand how kernel values affect the output. A number of sample kernels are included in this chapter. In addition, you will have the chance to update the work started with the Chapter 5 tutorial. In addition, you'll build a custom filter using existing effects and nodes.

Filter Matrices

As discussed in Chapter 5, using matrices is a necessary step when applying transformations to a layer or node output. Not only is position, rotation, skew, and scale information stored in a transformation matrix, but pixel averaging, which is required to prevent aliasing problems, is undertaken ...