Apple Shake 4 Tutorials - Manual (Page 173)

Chapter 5 Using Keylight 173
When the output is switched to “unpremult,” the composite looks terrible. This
unpremultiplied state is temporary, until you composite with an Over node.
2 To remove the background image input from Keylight1, Command-click or Control-click
the noodle.
Now use a Compress node with an Over node to re-composite the background.
3 In the Node View, select the Keylight1 node.
4 Attach a Color–Compress node.
The Compress node is used for the color correction.
5 Attach a Layer–Over node to the Compress1 node.
6 Connect the merlin_bg image to the second input of the Over1 node.