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When the object you want to matte has a markedly different luminance value than its
background, you can make the background value transparent by keying it out. 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 area.
To key out a luminance value:
1 Select the layer.
2 Choose Effect > Keying > Luma Key.
3 Select a Key Type to specify the range to be keyed out.
4 Drag the Threshold slider on the Effect Controls window to set the luminance value on
which you want the matte to be based.
5 Drag the Tolerance slider to specify the range of values to be keyed out. Lower values
key out a smaller range of values near the threshold. Higher values key out a wider range
of values.
6 Drag the Edge Thin slider to adjust the width of the keyed area's border. Positive values
make the mask grow, increasing the transparent area. Negative values shrink the mask.
7 Drag the Edge Feather slider to specify the softness of the edge. Higher values create a
softer edge but take longer to render.
Spill Suppressor (PB only)
The Spill Suppressor removes traces of the key color from an image with a screen that has
already been keyed out. Typically, the Spill Suppressor is used to remove key color spills
from the edges of an image. Spills are caused by light reflecting off the screen and onto
the subject.
If you are not satisfied with the results from using the Spill Suppressor, try applying the
Hue/Saturation effect to a layer after keying, and then decrease the saturation value to
de-emphasize the key color. (See "Hue/Saturation" on page 183.)
To apply the Spill Suppressor:
1 Select the layer and choose Effect > Keying > Spill Suppressor.
2 Choose the color you want to suppress in one of the following ways:
If you have already keyed out the color with a key in the Effects Window, click the Color
•
to Suppress eyedropper, and then click the screen color in the key's Key Color swatch.
In Spill Suppressor, click the Key Color swatch and choose a color from the color wheel.
•
3 In the Color Accuracy menu, choose Faster to suppress blue, green, or red. Choose
Better to suppress other colors, because After Effects may need to analyze the colors more
carefully to produce accurate transparency. The Better option may increase rendering
time.
4 Drag the Suppression slider until the color is adequately suppressed.
Matte Tools effects (PB only)
Use the matte tools to refine existing mattes. Matte tools should be applied and rendered
after the keys.
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