Apple Shake 4 - Manual (Page 692)

692 Chapter 24 Keying
A black line appears around the pillar.
As mentioned earlier, it is better to composite after pulling your key because it gives
you more flexibility.
7 So, rewire the tree with an Over node. Make sure you turn on preMultiply in the Over
node parameters and set the Keylight output to unPremult.
8 Next, attach a DilateErode node to the Keylight node.
9 In the DilateErode channels parameter, enter “a” (replace rgba) to affect only the alpha,
then set xPixels to -1. Note that the DilateErode node chews into the matte.