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Replace a static background with Difference Matte
The Difference Matte creates transparency
by comparing a specified still image with a specified clip and then
eliminating areas in the clip that match those in the image. This
key can be used to create special effects. Depending on the clip,
it’s possible to use Difference Matte to key out a static background
and replace it with another still or moving image.
You can
create the matte by saving a frame from a clip that shows the static background
before the moving object enters the scene. For best results, neither the
camera nor anything in the background should move.
The following
Difference Matte settings are adjusted in the Effect Controls panel:
- View
- Specifies whether the Program Monitor shows the Final Output,
Source Only, or Matte Only.
- Difference Layer
- Specifies the track to be used as the matte.
- If Layer Sizes Differ
- Specifies whether to center the foreground image or stretch
it to fit.
- Matching Tolerance
- Specifies the degree to which the matte must match the foreground
in order to be keyed.
- Matching Softness
- Specifies the degree of softness at the edges of the matte.
Note: The
RGB Difference Key uses color to define transparency much as the Difference
Matte uses a still image.
- Blur Before Difference
- Specifies the degree of blur added to the matte.
- Find a frame of your foreground clip that consists
only of the static background. You will use this frame as a matte.
Save this frame as an image file. It will appear in the Project
panel.
- Drag the matte frame from the Project panel to a video
track in a Timeline panel.
- Drag the clip you want to use as the background to a
track in a Timeline panel above the matte frame.
- Place the video clip you wish to use in the foreground
on a track in a Timeline panel above the background clip.
- (Optional) If you’re animating the Difference Matte over
time, make sure that the current‑time indicator is in the position
you want. Click the Toggle Animation icons
for
the settings you adjust.
- In the Effects panel, expand the Video Effects bin and
then the Keying bin.
- Drag the Difference Matte effect onto the foreground
video clip.
- In the Effect Controls panel, click the triangle next
to Difference Matte to expose its controls.
- From the Difference Layer drop-down menu, select the
track that contains the matte frame.
- Adjust the other settings as needed to achieve the desired
effect.
- (Optional) If you’re animating the Difference Matte,
move the current‑time indicator either in the Effect Controls panel
or Timeline panel and change the Image Matte settings.
A new keyframe appears in the Effect Controls timeline
when you change the settings. You can also adjust the interpolation
between keyframes by editing the keyframe graph. Repeat this step
as needed.
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