Apple Shake 4 Tutorials - Manual (Page 165)

Chapter 5 Using Keylight 165
5 In the Keylight parameters, click the screenColour control (the blue-colored box), then
drag the pointer across the lower portion of the greenscreen color in the Viewer.
The greenscreen color appears in the screenColour. (Although Keylight also works with
bluescreen backgrounds, it does not work well with secondary colors such as cyan,
magenta, or yellow.)
The result of your initial color pick is a fairly good key.
6 To view the alpha channel, position the pointer in the Viewer, then press A.
Testing the Mask With a Viewer Script
The quality of your mask cannot always be gauged visually for a number of reasons. For
one, monitor default settings differ from system to system. Depending on your gamma
settings, the your results match those shown in this tutorials. Therefore, when pulling a
key, it’s a good idea to test your results by applying a custom gamma lookup table.