Apple Shake 4 - Manual (Page 464)

464 Chapter 16 Compositing With Layer Nodes
KeyMix
The KeyMix node mixes two images together through the specified channel of a third
image. You can control the mix percentage, and also invert the masking image. KeyMix
and Over are the two primary compositing nodes—KeyMix for unpremultiplied images
and Over for premultiplied images.
For more information on premultiplication, see “ About Premultiplication and
Compositing ” on page 421.
Example
In the following node tree, by mixing through the RotoShape node, you can color
correct the beach and position the sky separately.
Parameters
This node displays the following controls in the Parameters tab:
clipMode
Toggles between the foreground (0) or the background (1) image to set the output
resolution.
Grad1 RotoShape1
Beach KeyMix1