User guide

KeylightThe Foundry
TUTORIAL
43
Tutorial 4: A Red Green Screen
Tutorial 4: A Red
Green Screen
Using the images from the film Executive Decision, you will learn how to pull
a key from a poor green screen using the Despill Bias control. You will learn
how to:
• Pick the Screen Colour.
• Drop the Screen Bias.
•Produce a final composite.
The images you will need for this tutorial are called ExecFG.tif and
ExecBG.tif
1. Load the pictures ExecFG.tif (Figure 75) and ExecBG.tif. Apply Keylight.
Figure 75. Poor Green Screen.
The foreground image is actually a green screen shot although it doesn’t
look it. If you analyse the pixels it’s slightly more red than green. To key
this we’ll have to fool Keylight.
2. Pick the Screen Colour. You should go for the slightly darker green patch
to the left of the pilot. Although feel free to experiment picking different
parts of the green screen. The initial selection gives the result shown in
Figure 76.
Figure 76. Default key.
3. To fix this we need to tell Keylight to scale down the red component to
make the green the most dominant so that it keys correctly. To do this
decrease the Despill Bias to -20. The result is shown in
Figure 77 on
page 44.