Graphics Reference
In-Depth Information
1.
Add this node by pressing Shift+A and choosing Color > Mix from the menu and then choosing Sub-
tract from the drop-down menu on the node. Because there is proportionately less red in the background,
this step results in darkening the foreground considerably more than the background, as you can see in
Figure 9-43
.
This correctly separates the foreground from the background.
Figure 9-43
Subtracting the red channel from the green channel
2.
Next add a ColorRamp node by pressing the spacebar and choosing Add > Converter > ColorRamp.
3.
Instead of manually connecting the color ramp, you can insert it directly into the noodle by dragging
it over the link between your Subtract node and your Viewer node. Use this as shown in
Figure 9-44
to
invert the light and dark areas and to push the contrast to solid black and white.
4.
By adjusting the location of the value change along the length of the color ramp, you can adjust where
along the grayscale range the black/white split occurs. This has the effect of enlarging or shrinking the
black and white areas in the image. The resulting green screen matte should look something like the one
shown in
Figure 9-45
.
