Node-based compositing is different from the layer-based system familiar to many NLE editors. Unlike layers, in which the visuals are compounded based on their order in the layer stack, nodes process a single RGB signal, modifying it along the way.
As each node affects the image, it outputs the altered signal via an RGB link until the final RGB data reaches the output node of the Node editor. This output node represents the image in its final state and is what the colorist sees in the viewer, and how the media will look upon being rendered.
Nodes are capable of reusing information from previous nodes, substantially reducing the amount of processing power required to assemble and output a final image. This is particularly useful when working with keys, such as those generated by qualifiers and Power Windows.
The Anatomy of a Node
The Node graph is read from left to right. The RGB signal that constitutes the visual information of the image beings at the leftmost green node, the RGB input, and travels via the links that connect the corrector nodes until it reaches the final node tree output on the right-hand side. The RGB signal must be uninterrupted for the grades to be correctly compiled and output.
Standard corrector nodes have two inputs and two outputs.
The green triangle and square shapes at the top of either side are the RGB inputs and outputs. These carry the pixel data of the image, which is manipulated within the node using the grading tools of the Color page. Corrector nodes can only accept one RGB input but can output multiple RGB signals to other nodes.
The blue shapes are the key inputs and outputs. These enable you to transfer the key data generated by the Power Windows and qualifiers (or external mattes) to be used by other nodes.
Understanding the Importance of Node Order
The RGB signal output of each node carries the full weight of its grade and directly affects the next node’s interaction with it. The following set of exercises are designed to demonstrate how nodes impact one another.
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