Adobe After Effects CS3 - Manual (Page 450)

AFTER EFFECTS CS3
User Guide
445
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 transparency; higher values produce more transparency.
10 Adjust the Matching Softness slider to soften the edges between transparent and opaque areas. Higher values
make matched pixels more transparent but don’t increase the number of matching pixels.
11 If the matte still contains extraneous pixels, adjust the Blur Before Difference slider. This slider suppresses noise
by slightly blurring both layers before the comparison is made. Note that the blurring occurs only for the comparison
and doesn’t blur final output.
12 Before closing the Effect Controls panel, make sure to select Final Output from the View menu to ensure that
After Effects renders the transparency.
Extract effect
The Extract effect creates transparency by keying out a specified brightness range, based on a histogram of a
specified channel. It’s 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.
Note: The controls for this effect are similar to those of the Extract effect in Adobe Premiere Pro, but the purpose and
results of the effect are different.
This effect works with 8-bpc and 16-bpc color.
See also
“Keying overview and tips” on page 268
“Matte Choker effect” on page 450
“Simple Choker effect” on page 451
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.
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 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).