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Stretch to Fit stretches or shrinks the difference layer to the size of the source layer, but
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it may distort background images.
9 Adjust the Matching Tolerance slider to specify the amount of transparency based on
how closely colors must match between the layers. Lower values produce less trans-
parency; higher values produce more.
10 Adjust the Matching Softness slider to soften the edges between transparent and
opaque areas. Higher values make matched pixels more transparent, but do not increase
the number of matching pixels.
11 If there are still extraneous pixels in the matte, adjust the Blur Before Difference slider.
This option suppresses noise by slightly blurring both layers before making the
comparison. Note that the blurring occurs only for comparison and does not blur final
output.
12 Before closing the Effect Controls window, make sure that you have selected Final
Output from the View menu to ensure that After Effects renders the transparency.
Extract (PB only)
This effect creates transparency by keying out (or extracting) a specified brightness range,
based on a histogram of a specified channel. It is best used to create transparency in an
image shot against a black or white background or against a background that is very dark
or bright but consists of more than one color. You can also use it to remove shadows from
a composition.
In the Effect Controls window, 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 transparent. 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 trans-
parent.
To apply Extract:
1 Select the layer you want to make transparent, and then choose Effect > Keying >
Extract.
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.
3 Adjust the amount of transparency by dragging the transparency control bar in the
following ways:
Drag the upper right and upper left selection handles to adjust the length of the bar to
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shorten or lengthen the transparency range. You can also adjust the length by moving
the White Point and Black Point slider bars. Values above the white point and below the
black point are made transparent.
Drag the lower right and lower left selection handles to taper the bar. Tapering the bar
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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
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