Adobe After Effects CS3 - Manual (Page 452)

AFTER EFFECTS CS3
User Guide
447
7 Specify the Edge Threshold, which is a soft cutoff for removing low-opacity pixels that can cause unwanted noise
in the image background.
8 Select Invert Extraction to reverse the foreground and background regions.
9 Set Blend With Original to specify the degree to which the resulting extracted image blends with the original
image.
Linear Color Key effect
Linear keys create a range of transparency across an image. A linear key compares each pixel in the image to the key
color you specify. If the color of a pixel closely matches the key color, it becomes completely transparent. Pixels that
don’t match as well are made less transparent, and pixels that don’t match at all remain opaque. The range of trans-
parency values, therefore, forms a linear progression.
The Linear Color Key effect uses RGB, hue, or chroma information to create transparency from a specified key color.
This effect works with 8-bpc, 16-bpc, and 32-bpc color.
See also
“Keying overview and tips” on page 268
“Matte Choker effect” on page 450
“Simple Choker effect” on page 451
Apply the Linear Color Key effect
In the Effect Controls panel, the Linear Color Key effect displays two thumbnail images; the left thumbnail image repre-
sents the unaltered source image, and the right thumbnail image represents the view you’ve selected in the View menu.
You can adjust the key color, the matching tolerance, and the matching softness. The matching tolerance specifies
how closely pixels must match the key color before they start becoming transparent. The matching softness controls
the softness of edges between the image and the key color.
You can also reapply this key to preserve a color that was made transparent by the first application of the key. For
example, if you key out a medium-blue screen, you might lose some or all of a light-blue piece of clothing your
subject is wearing. You can bring back the light-blue color by applying another instance of the Linear Color Key and
choosing Keep This Color from the Key Operation menu.
1 Select a layer as the source layer, and then choose Effect > Keying > Linear Color Key.
2 In the Effect Controls panel, choose Key Colors from the Key Operation menu.
3 Choose a color space from the Match Colors menu. In most cases, use the default RGB setting. If you have trouble
isolating the subject using one color space, try using a different color space.
4 In the Effect Controls panel, choose Final Output from the View menu. The view you choose appears in the right
thumbnail and in the Composition panel. If you need to see other results, work in one of the other views:
Source Only Shows the original image without the key applied.
Matte Only Shows the alpha channel matte. Use this view to check for holes in the transparency. To fill undesired
holes after you complete the keying process, see “Close a hole in a matte” on page 271.