Adobe 65008009 - After Effects CS4 Using Manual page 518

Last updated 12/21/2009
In addition to masking a soft-edged object from its background, Inner/Outer Key modifies the colors around the
border to remove contaminating background colors. This color decontamination process determines the contribution
of the background to the color in each border pixel, and then removes that contribution—thus removing the halo that
can appear if a soft-edged object is matted against a new background.
Select the border of the object that you want to extract by doing one of the following:
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• Draw a single closed mask near the border of the object; then select the mask from the Foreground menu and leave
the Background menu set to None. Adjust the Single Mask Highlight Radius to control the size of the border around
this mask. (This method works well only on objects with simple edges.)
• Draw two closed masks: an inner mask just inside the object, and an outer mask just outside the object. Make sure
that any fuzzy or uncertain areas of the object lie within these two masks. Select the inner mask from the
Foreground menu and the outer mask from the Background menu.
Note: Make sure that the mask mode for all masks is set to None.
If you want, move the masks around to find the location that provides the best results.
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To extract more than one object, or to create a hole in an object, draw additional masks and then select them from
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the Additional Foreground and Additional Background menus. For example, to key out a person's hair blowing in
the wind against a blue sky, draw the inner mask inside the head, draw the outer mask around the outside edge of
the hair, and then draw an additional mask around the gap in the hair where you can see sky. Select the additional
mask from the Additional Foreground menu to extract the gap and remove the background image.
Create additional open or closed masks to clean up other areas of the image, and then select them from the Cleanup
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Foreground or Cleanup Background menu. Cleanup Foreground masks increase the opacity along the mask;
Cleanup Background masks decrease the opacity along the mask. Use the Brush Radius and Brush Pressure options
to control the size and density of each stroke.
Note: You can select the Background (outer) mask as a Cleanup Background mask to clean up noise from the background
portions of the image.
Set Edge Thin to specify how much of the border of the matte is affected by the key. A positive value moves the edge
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away from the transparent region, increasing the transparent area; a negative value moves the edge toward the
transparent region and increases the size of the foreground area.
6 Increase the Edge Feather values to soften edges of the keyed area. High Edge Feather values take longer to render.
Specify the Edge Threshold, which is a soft cutoff for removing low-opacity pixels that can cause unwanted noise
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in the image background.
8 Select Invert Extraction to reverse the foreground and background regions.
Set Blend With Original to specify the degree to which the resulting extracted image blends with the original image.
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Linear Color Key effect
Note: Though the color keying effects built into After Effects can be useful for some purposes, you should try keying with
Keylight before attempting to use these built-in keying effects. Some keying effects have been superseded by more modern
effects like Keylight.
For information about keying in general, including links to tutorials and other resources, see
resources" on page 383.
Linear keys create a range of transparency across an image. A linear key compares each pixel in the image to the key
color you specify. If the color of a pixel closely matches the key color, it becomes completely transparent. Pixels that
don't match as well are made less transparent, and pixels that don't match at all remain opaque. The range of
transparency values, therefore, forms a linear progression.
USING AFTER EFFECTS CS4
Effects and animation presets
"Keying introduction and
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