Nuke Basics: Shuffle and ShuffleCopy
This is very embarrassing to admit, but when I started compositing, I really didn't understand what an Alpha Channel was. I also would constantly confuse 'the part that goes away' with white and black. Did the white part keep the image, or did the black part keep it? It took a while to sink in, maybe two or three years...
There were two books that really helped me understand things. One was Digital Compositing for Film and Video by Steve Wright, the other was Photoshop Channel Chops by David Biedny, Nathan Moody and Bert Monroy. I just checked my Amazon account, and I bought those books just over ten years ago. They are just as relevant now as they were back then.
Understanding Channels is a essencial principle of compositing. Channels are the building blocks of our images, being able to change and manipulate them is critical. Nuke allows you to have over a thousand channels inside your comp at any one time. The Shuffle and ShuffleCopy nodes allow you to move your channels from one image buffer to another. The tutorial above explains how.