Using A Hold-Out Matte; To Create A Hold-Out Matte - Adobe AFTER EFFECTS 7.0 Manual

Using a hold-out matte

A hold-out matte (also known as a hold-back matte) is a duplicate of the layer you have keyed. The hold-out matte,
however, is masked to include only the area of the image containing the key color that you want to preserve as
opaque. The hold-out matte is then placed directly on top of the keyed layer; when rendered, the hold-out matte
prevents the area from becoming transparent.
Typically, you would create a hold-out matte for only one or two frames, when the subject is in a particular position
that makes the color visible. Hold-out mattes are not recommended for preserving color for longer periods of time
because the effect may become more obviously visible.
A
C
Example of using a hold-out matte
A. Original bluescreen image. The number's background is also blue. B. After keying, the number's background is also transparent. C. Hold-
out matte containing the part of the image you want to remain opaque D. When the hold-out matte is placed on top of the keyed image, the
number's background is now opaque.
See also
"About keying" on page 270

To create a hold-out matte

1 Apply any Transform property keyframes to the original layer containing the color screen.
Duplicate the layer containing the color screen.
2
3 In the original, apply keys and Matte effects to create transparency.
In the copy, find the frame that contains the area you want to preserve, and then create a mask to mask out every-
4
thing in the image except the area you want to preserve.
5 Make sure that the copy (the hold-out matte) is positioned directly on top of the keyed layer and contains exactly
the same keyframes with the same values. Then render the movie.
See also
"Creating masks" on page 244
"About keying" on page 270
B
D
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