Subtractive Tracking in silhouette


Is there a way to subtract information from a track when using the mocha tracking in silhouette?
For example if a hand moves in front of an object you are trying to track. I know you can subtract the roto layers which will subtract the alpha but dosn’t seem to effect the tracking results. I am sure I did this with SFX v6 and it effected the tracking results but I could be miss-remembering… Any help to be able to subtractive track in SFX v7.5 would be great. Thanks :slight_smile:

The workflow to do this is described on page 108 of the Silhouette User Guide. Instructions to do this are below.

Exclude Areas While Planar Tracking

In some cases, there are parts of an image that can interfere with the effectiveness of the Planar or mocha Trackers. To handle this, you can create subtractive shapes in the area you are tracking.

  1. Create a shape around the area that you would like to exclude from the tracking process.
  2. Place this shape above the layer that you are tracking. Set the shape’s Blend mode to Subtract.
  3. Select the layer you are tracking and then add the subtract shape to the selection by using Ctrl(Win)/Cmd(Mac)-click.
    Note: The same method used for shapes to exclude areas while tracking can be used for layers.
  4. Hit either the forward or backward track button depending on which direction you are tracking.

Now, the area within the subtract shape is not analyzed by the Planar Tracker or mocha Tracker.

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Thanks for your help, I was forgetting the ctrl + click.