Adobe After Effects CS3 - Manual (Page 451)

AFTER EFFECTS CS3
User Guide
446
Note: To taper the edges of the transparency control bar, you must first shorten the transparency bar.
• Drag the entire bar left or right to position it under the histogram.
Inner/Outer Key effect
The Inner/Outer Key effect isolates a foreground object from its background.
This effect works with 8-bpc and 16-bpc color.
See also
“Keying overview and tips” on page 268
Use the Inner/Outer Key effect
To use the Inner/Outer key, create a mask to define the inside and outside edge of the object you want to isolate. The
mask can be fairly rough—it doesn’t need to fit exactly around the edges of the object.
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
background's contribution 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.
1 Select the border of the object that you want to extract by doing one of the following:
• Draw a single closed mask near the object's border; 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.
2 If you want, move the masks around to find the location that provides the best results.
3 To extract more than one object, or to create a hole in an object, draw additional masks and then select them from
the Additional Foreground and Additional Background menus. For example, to key out a woman’s hair blowing in
the wind against a blue sky, draw the inner mask inside her head, draw the outer mask around the outside edge of
her hair, and then draw an additional mask around the gap in her hair where you can see sky. Select the additional
mask from the Additional Foreground menu to extract the gap and remove the background image.
4 Create additional open or closed masks to clean up other areas of the image, and then select them from the
Cleanup 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.
5 Set Edge Thin to specify how much of the matte’s border is affected by the key. A positive value moves the edge
away from the transparent region, increasing the transparent area; a negative value moves the edge toward the trans-
parent 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.