Adobe AFTER EFFECTS CS3 PROFESSIONAL User Manual page 449

Use the Extract effect
In the Effect Controls panel, the Extract effect displays a histogram for a channel specified in the Channel menu. The
histogram displays a representation of the brightness levels in the layer, showing the relative number of pixels at each
level. From left to right, the histogram extends from the darkest (a value of 0) to the lightest (a value of 255).
Using the transparency control bar beneath the histogram, you can adjust the range of pixels that are made trans-
parent. The position and shape of the bar in relation to the histogram determine transparency. Pixels corresponding
to the area covered by the bar remain opaque; pixels corresponding to the areas not covered by the bar are made
transparent.
Select the layer you want to make transparent, and then choose Effect > Keying > Extract.
1
2 If you are keying out bright or dark areas, choose Luminance from the Channel menu. To create visual effects,
choose Red, Green, Blue, or Alpha.
Adjust the amount of transparency by dragging the transparency control bar in the following ways:
3
• Drag the upper right or upper left selection handles to adjust the length of the bar and to shorten or lengthen the
transparency range. You can also adjust the length by moving the White Point and Black Point sliders. Values
above the white point and below the black point are made transparent.
• Drag the lower right or lower left selection handles to taper the bar. Tapering the bar on the left affects the softness
of transparency in the darker areas of the image; tapering it on the right affects the softness in the lighter areas.
You can also adjust the softness levels by adjusting White Softness (lighter areas) and Black Softness (darker areas).
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" 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.
AFTER EFFECTS CS3 443
User Guide