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Mask out objects with garbage mattes

Sometimes the subject of a scene is properly keyed except for undesired objects. Use a garbage matte to mask out those objects. Depending on the shape of the mask, you can use the Four‑Point Garbage Matte, Eight‑Point Garbage Matte, or Sixteen‑Point Garbage Matte. More points let you define more complex mask shapes.

The Garbage Matte keying effect provides settings that represent the x and y pixel coordinates of each point of the garbage matte, measured from the top left corner of the frame. Changes appear in the Preview view of the Program Monitor.

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The microphone (left) is masked out by repositioning image handles in the Preview view of the Program Monitor (center), creating a garbage matte that is then keyed and superimposed over a background (right).

  1. In a Timeline panel, place the clip you want to superimpose in a track above the one containing the background clip.
  2. In the Effects panel, click the triangle to expand the Video Effects bin and then click the triangle to expand the Keying bin.
  3. Drag either the Eight‑Point Garbage Matte, the Four‑Point Garbage Matte, or the Sixteen‑Point Garbage Matte effect to the superimposed clip.

    Your choice of garbage matte depends on the number of points needed for mask shape.

  4. In the Effect Controls panel, click the triangle next to the Garbage Matte name to expand the settings.
  5. (Optional) If you’re animating the Garbage Matte Key over time, make sure that the current‑time indicator is in the position you want. Click the Toggle Animation icons for the position settings you plan to adjust.
  6. Do any of the following to adjust the mask shape:

    • With the Garbage Matte effect selected in the Effect Controls panel, drag the Garbage Matte handles in the Program Monitor.

    • Adjust the Garbage Matte point settings in the Effect Controls panel to specify the size and position of the garbage matte.

  7. (Optional) If you’re animating the Garbage Matte Key, move the current‑time indicator either in the Effect Controls panel or a Timeline panel and then change the Garbage Matte handle positions in the Program Monitor or adjust the settings in the Effect Controls panel.

    A new keyframe appears in the Effect Controls timeline when you move the handles in the Program monitor or change the settings in the Effect Controls panel. You can also adjust the interpolation between keyframes by editing the keyframe graph. Repeat this step as needed.