The Inner/Outer Key effect isolates a
foreground object from its background.
This effect works with 8-bpc and 16-bpc color.
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.
- 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.
- If you want, move the masks around to find the location
that provides the best results.
- 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.
- 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.
- 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 transparent region and increases
the size of the foreground area.
- 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 in the
image background.
- 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.
Use the Inner/Outer Key effect