Chapter 4. Channel Manipulation
"Understand color and the way computers display images. Try to understand not just what buttons to push, but the underlying and relatively simple math that's happening under the hood."
Channel manipulation gives a compositor a great deal of control over every step of a composite. While alpha channels are the subject of considerable manipulation, other channels, such as color, luminance, and chrominance, are equally useful. After Effects and Nuke provide a wide array of channel manipulation effects and nodes, including those designed for channel copying and swapping, channel math operations, color space conversions, and color correction. To apply these tools successfully, it helps to understand the underlying math and modes of operations. To assist you in judging the result, histograms are an important device. To practice these concepts, this chapter includes After Effects and Nuke tutorials that integrate CG into degraded live-action footage. In addition, the Chapter 3 Nuke tutorial, which covers greenscreen removal, is revisited.
Histograms and Tonal Ranges
An image histogram is a graphical representation of tonal distribution. Histograms plot the number of pixels that possess ...