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Using the Outputs of a Tracker
The tracker outputs described above are published by each tracker pattern created in the Tracker node. Each Tracker node itself also publishes a Steady Position, Angle, Size and an Unsteady Position. The values of these Tracker node outputs are calculated using all the patterns in that tracker, as configured by the Match Move Settings controls in the Tracker’s Operation tab.
The Match Move settings determine the reference frame for stabilization and the point around which stabilization pivots
Rather than using the Tracker node to perform the Merge operation, an alternative and common way to use these published outputs is to create a match move by connecting the outputs to multiple nodes. A tracker is used to track a pattern, and then that data can be connected to multiple other nodes using the Connect To submenu.
1 Track the background clip using at least two tracking patterns in the tracker.
2 In a different branch, add a Transform node to the background clip.
The background branched to go to a Tracker and a Transform
3 Right-click over the Transform’s Center and choose Connect to > Tracker1 > Steady Position.
The tracker publishes its output for other nodes to connect to, as done here to stabilize the clip
4 Connect the foreground to a corner-positioned node, so you can position the corners of the foreground appropriately over the background.
5 Add another Transform node to the Node Editor after the Merge.
A second Transform after the Merge is used to add back in the original motion with Unsteady Poisition
6 Connect the new Transform’s Center to the Tracker’s Unsteady Position. The image will be restored to its original state with the additional effect included.
To better understand how this works, imagine a pattern that is selected at frame 1, at position 0.5,
0.5. The pattern does not move on frame 2, so its position is still 0.5, 0.5. On the third frame, it moves 10 percent of the image’s width to the right. Now its position is 0.6, 0.5.
If a transform center is connected to the Steady Position output of the Tracker, the Transform node’s center is 0.5, 0.5 on the first and second frames because there has been no change. On frame 3, the center moves to 0.4, 0.5. This is the inverse of the horizontal motion that was tracked in the pattern, moving the image slightly to the right by 10 percent of the image width to counteract the movement and return the pattern of pixels back to where they were found.