Keying - Nuke 101: Professional Compositing and Visual Effects - page 328

The matte defines areas that need to remain as part of the foreground rather than
be thrown out, as usually it's the white areas that define a shape and not the black
areas. If you invert this image, it will then define the areas that are garbage.
6. From the Color toolbox, insert an Invert node after Blur1.
NowthegarbagematteandthemattecomingoutoftheIBKneedtobecombined.
You will use a regular Merge node for that.
7. Click Invert1 and then Shift-click IBKGizmoV3_1. The order is important as it
defines which will end up being the A input and which the B.
8. Press the M key to insert a Merge node ( FIGURE 7.38 ).
Figure 7.38. The Merge node is supposed to be connected like this.
9. In Merge2, choose Stencil from the Operation drop-down menu ( FIGURE 7.39 ) .
Figure 7.39. Changing the Operation from Over to Stencil.