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(Left) An entire clip with a high-contrast grade, (Right) The skin tone graded differently from the high-contrast grade using a key
This example could have been handled in a variety of different ways, but the point is that you can add nodes that connect to the state of the image at any part of a node tree, and use them to generate keys to feed to any other node, regardless of what’s happening to the picture in between.
Connecting Key Outputs to RGB Inputs, and Vice Versa
There’s another way you can manipulate a key from one node using another in the Node Editor, and that’s to connect the key output from one node to the RGB input of another node. When you do this, you can use any of the controls of the second node to manipulate the key, and you can then use the result by connecting the RGB output of the second node to the key input of a third node.
Connecting a key output to an RGB input to adjust a key with a second node’s controls
In the node tree shown above, Node 2 pulls a key, Node 4 manipulates the key, and Node 3 uses the key to make a color adjustment.
Keep in mind that a key is just a grayscale image. Setting up this kind of node structure lets you use any of the second node’s controls, such as the Custom Curves, Noise Reduction or Motion Blur controls, Sharpen, Midtone Contrast, Lift/Gamma/Gain, Contrast, or Log controls, to manipulate the key in ways you couldn’t do using only the Matte Finesse controls.
While this technique may not be necessary for conventional color isolations, it can come in very handy when making tricky isolations with hard to key subjects, or when using one of the Qualifier modes to pull a key to create transparency for compositing using the Node Editor’s Alpha output. In this instance, you can connect the RGB output of a node used for key manipulation directly to the Alpha output. In the example, Node 1 pulls a key, and the RGB is connected to Node 3 which is used to color correct the foreground image. The key from Node 1 is connected to the RGB of
Node 2, which manipulates the key to clean it up prior to connecting it to the Alpha output block at the bottom right of the Node Editor.
Connecting a key output to an RGB input to adjust a key used to create transparency via the Alpha output
Furthermore, this capability also lets you create keys in other ways besides using the Qualifier palette controls. In the following example, the Contrast and Custom Curve controls in Node
3 create a high-contrast matte of the windows which is blurred. The RGB output of Node 3 is then connected to the KEY input of Node 2, where the resulting key can be used for a variety of adjustments; in this case, to tint the product within the image green. Alternately, this technique could be also be used to create transparency via the Alpha output.
Using a high-contrast color correction as a key
You can manually connect RGB inputs and outputs to Key inputs and outputs by dragging links between them. Alternatively, you can drag and hover a node over an RGB or Key link to insert it. Interconnecting key and RGB inputs and outputs is a powerful capability that lets you create many kinds of workarounds for uncommon situations.