Keying - Nuke 101: Professional Compositing and Visual Effects - page 321

Here you see four properties. The bottom three are Gain controls for the three
dynamic ranges: shadows, midtones, and highlights. The first property defines
where the midtones are—if this were a generally dark image, the midtones would
be lower.
11. Bring up the Shadow Gain property to about 1.1. This should eliminate most of
the grays in the background area.
Note
Ifyourmattelooksdifferentthanmine,thatmeansyoupickeddiffer-
entcolorsfortheScreenColourproperty.That'sOK.Butyou'llhave
toplayaroundwiththeShadowGain,MidtonesGain,andHighlights
Gain properties to make the foreground areas white and the back-
ground areas black. The Screen Matte properties, which I explain in
the next step will also need to be adjusted in a different way.
Keylight offers a lot of additional controls. Under the Screen Matte submenu you
find properties that control the matte after its keying process creation. I call these
the post key operations, as they are actually operations that happen on the pro-
duced matte rather than using any keying process.
12. Click the arrow next to Tuning to hide those controls, and then click the arrow
next to Screen Matte to display those options instead ( FIGURE 7.31 ) .
Figure 7.31. The Screen Matte options.