Apple Shake 4 - Manual (Page 539)

Chapter 19 Using Masks 539
7 Connect the SwitchMatte node to the Background input of the Atop node.
If the image looks wrong, make sure that matteMult is disabled, and invertMatte is
enabled in the SwitchMatte node parameters.
Masking Filters
Filters have special masked versions of the node that not only mask an effect, but also
change the amount of filtering based on the intensity of the second image. These take
the same name as the normal filter node preceded by an I, for example, Blur and IBlur.
This is much more convincing than using the mask input.
To mask a filter:
1 Create an Image–Text node, and type some text in the text field. (Type in the second
field labeled “text” since the first field is to change the name of the node.)
2 Adjust the xFontScale and yFontScale parameters so the text fills the frame.
3 Create an Image–Ramp, and set the alpha1 parameter to 0.
4 Select the Text node, and add a Filter–Blur node.
5 Connect the Ramp node to the M input of the Blur node.