Apple Shake 4 Tutorials - Manual (Page 256)

256 Tutorial 9 Creating Clean Plates
The images are aligned when most of the background noise disappears.
7 In the Node View, select the Invert1 node, then press Delete.
8 Select the Mix1 node, then Command-click or Control-click the QuickPaint command
button in the Image tab.
The Mix1 node is replaced by the QuickPaint1 node.
The next step is important:
Not aligned Aligned