Adobe AFTER EFFECTS CS3 PROFESSIONAL User Manual page 452

Preserve a color after applying Linear Color Key
1 In the Effect Controls panel or Timeline panel, turn off any current instances of keys or matte effects by
deselecting the Effect option to the left of the key name or tool name. Deselecting the option causes the original
image to appear in the Composition panel so that you can select a color to preserve.
Choose Effect > Keying > Linear Color Key. A second set of Linear Color Key controls appears in the Effect
2
Controls panel below the first set.
3 In the Effect Controls panel, choose Keep Colors from the Key Operation menu.
Select the color you want to keep.
4
In the first application of the Linear Color Key effect, choose Final Output from the View menu in the Effect
5
Controls panel, and then turn other instances of the Linear Color Key effect back on to examine the transparency.
You may need to adjust colors or reapply the key a third time to get the results you need.
Luma Key effect
The Luma Key effect keys out all the regions of a layer with a specified luminance or brightness. The layer's quality
setting doesn't influence the Luma Key effect.
Use this effect if the object from which you want to create a matte has a greatly different luminance value than its
background. For example, if you want to create a matte for musical notes on a white background, you can key out
the brighter values; the dark musical notes become the only opaque areas.
This effect works with 8-bpc and 16-bpc color.
White background of original (top left and bottom left) is removed using Luma Key and composited over underlying layer (bottom right).
See also
"Keying overview" on page 268
"Matte Choker effect" on page 448
"Simple Choker effect" on page 448
Key out a luminance value with the Luma Key effect
Select the layer, and choose Effect > Keying > Luma Key.
1
Select a Key Type to specify the range to be keyed out.
2
3 Drag the Threshold slider in the Effect Controls panel to set the luminance value you want the matte to be based on.
AFTER EFFECTS CS3 446
User Guide