Understanding Nodes

When you take a simple render (simple means a raw render, with no compositing involved), your scene is the input and the output will be the same as the input. When you enable the use of nodes, the input and the output are connected, but you can modify the final result by adding nodes in between that will apply effects and changes to the input before it reaches the output. The modifications can be as simple as color corrections or as complex as adding visual effects or mixing several different renders into a single render.

A node structure is often called a node tree, as its connections resemble branches that ultimately connect to form a single output—the tree’s trunk. In Figure 14.2, you can see a basic scheme of how a node tree can evolve as you add more nodes to the tree. The first node tree shows a basic setup, which is what you get when you enable Node Editing. The second tree adds a modification to the input before it reaches the output. The third tree mixes a second input into the result. You can see why it’s called a node tree because it now has two branches and this is only a basic setup; a complex scene can have dozens of different branches that interact together.

Figure 14.2 A scheme representing three different node trees that could also represent the same tree in different stages of its evolution

The basic thing you need to understand about a node tree is that it is processed from left to right. You can always add more nodes between other nodes. Let’s take the example shown in Figure 14.2: Each one of the inputs can be different renders of different parts of the scene. At the bottom of the figure, the first Input has a process going on before it’s mixed with the second Input, which could be a color correction for example. Imagine you want to make your whole render look more reddish or have more contrast: you could just add a new color correction node between the Mix node and the Output; the color correction node will then affect all the previous nodes after the mix happens.

If you pick any node, here is what happens: the data from another node enters the current node via the Input and is processed by the node using the properties set by the user. The data is then passed along to the output node where it can be viewed, or passed into yet another node.

If you still don’t get it, that’s perfectly normal. Sometimes you just need to get your hands on something to really understand it. As you continue this chapter and see what nodes are all about, and then create your first node tree, you’ll be able to see how your changes affect the overall result, which will answer a lot of your questions.