Apple Shake 4 User Manual
Page 425
Chapter 15
Image Processing Basics
425
The result is identical to munch_premult—the RGB is multiplied by the mask.
Next, invert the foreground alpha channel (
1-A
).
3
To do this, select the munch_mask node, then Shift-click the Color–Invert node.
The Invert node is attached to the munch_mask node as a separate branch.
The next step in the formula (
(1-A)*Bg
) calls for you to multiply the background by
the inverted alpha.
4
In the Node View, select the Invert node, then click Layer–IMult.
An IMult node is added to the Invert node.
5
Connect the bg node to the Background input of the IMult2 node.
Next, the crucial step—add the two results together.
6
In the Node View, select IMult1, then click Layer–IAdd. Connect the IMult2 node to the
background input of the IAdd node.
Comp
= (Fg * A) + ((1-A)*Bg)
Tree
IMult2