Restore part of a foreground image using a holdout mask
Sometimes, while pulling a key, you lose part of the image you’re trying to keep. This can happen when the color of the subject’s clothing is too close to the color of the background being keyed out, or when you need to use keying values that are too aggressive. In this example, small parts of the bird’s head and wings are getting removed with the key, rather than just the blue sky. If left uncorrected, the background image will show through the bird in these areas.
In these cases, you can duplicate the original layer, mask the part of the subject that’s being incorrectly keyed, and composite it over the keyed version to fill it back in.
Note: The Spill Suppressor filter can modify the color of the foreground subject as well. If you’re using the Spill Suppressor filter on the keyed layer, you may have to apply the same filter to the holdout mask layer to make sure the color matches. For more information on the Spill Suppressor filter, see Spill Suppression filter controls.
Create a holdout mask
Apply a Keyer filter to the foreground subject.
For more information about using Motion’s Keyer filter, see Keyer filter overview.
Duplicate the keyed layer.
On the newly duplicated layer (above the original layer in the Layers list or Timeline), delete the original keying filters.
If you’ve used a Spill Suppressor filter, don’t delete it, because it’s probably changing the color of the subject.
On the newly duplicated layer, use a mask-drawing tool to mask the area of the foreground that is incorrectly keyed.
Make sure that the mask is entirely within the subject being keyed.
Note: If the subject is moving, the holdout mask must be animated.
If necessary, feather the edge of the mask you’ve just created, to make sure that it blends in with the object you initially keyed.
In the following image, a clean key is created within the mask by removing the “dirt” left by the original key.
As an optional step, you can nest the originally keyed layer and the holdout mask you just created inside a dedicated group so you can manipulate the entire subject as a single object.