Use a garbage matte, Use a hold-out matte – Adobe After Effects CS3 User Manual
Page 275
AFTER EFFECTS CS3
User Guide
270
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To key well-lit footage shot against multiple colors or unevenly lit footage shot against a bluescreen or greenscreen,
start with the Color Range key. Add the Spill Suppressor and other effects to refine the matte. If you are not
completely satisfied with the results, try starting with or adding the Linear Color Key.
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To key dark areas or shadows, use the Extract Key on the Luminance channel.
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To make a static background scene transparent, use the Difference Matte Key. Add the Simple Choker and other
effects as needed to refine the matte.
For tips on shooting footage so that color keying is easier and more successful, see Jonas Hummelstrand’s website:
See also
Use a garbage matte
A garbage matte removes unneeded portions of the scene, resulting in a rough area that contains only the subject that
you want to keep. When you are working with a poorly lit or uneven bluescreen or greenscreen, sketching a garbage
matte around the subject can greatly reduce the amount of work that you have to do in keying out the background.
However, if you spend a lot of time making a perfect garbage matte that exactly outlines the subject—essentially
rotoscoping—you lose the time-saving advantage of color keying.
1
Create a mask to roughly outline a subject.
2
Apply one or more keying effects to mask out the remainder of the background.
3
Apply Matte effects as necessary to fine-tune the matte.
Aharon Rabinowitz shows how to create a super-tight garbage matte using Auto-trace in this video tutorial:
See also
“Creating and importing masks” on page 254
“Keying overview and tips” on page 268
Use a hold-out matte
Use a hold-out matte (also known as a hold-back matte) to patch a scene to which a keying effect has been applied.
A hold-out matte is a masked-out portion of a duplicate of a layer that you have keyed. The duplicate is masked to
include only the area of the image that contains the key color that you want to preserve as opaque. The hold-out matte
is then placed directly on top of the keyed layer.