Using the Right Motion Tracking Method for Your Shot

In this guide, world-renowned visual effects expert Lee Lanier from the learning platform Lowepost walks you through the most common tracking types available in modern compositing applications.

No single tracking type works with all shots, and as a compositor it’s important to learn which tracker works the best in each situation.

Transform Tracking

Transform tracking is the simples tracker available in most applications and occurs in 2D. It's able to track the X (left/right) and Y (up/down) motion of a pattern over time. This type of tracking is often called Matchmoving, as you can use it to impart motion to a new element as if it was shot with the original real-world camera.

For example, if you want to add a moon to a shot of a sky where the camera has minimal movement, such as a short pan, dolly, or hand-held tilt, transform tracking is a good choice.

Although it's often only necessary to use one tracking point to track one feature, you can use two points to track two features to detect simple rotation and scale changes. The rotation must stay “flat” to the camera, rotation along the camera's Z-axis, and scale changes are limited to those created when the camera zooms or changes its distance from the tracked feature.

See Tracking and Stabilizing on Foundry Learn for more information.

Corner-Pin Tracking

This tracking method builds upon transform tracking by adding three more track points for a total of four, it tracks four separate patterns over time. It's ideal for tracking anything rectangular, such as a door, window, poster, billboard, or iPad screen.

Although each track point operates in 2D (in the XY directions), having a total of four points allows the tracker to detect perspective or rotational changes to the rectangular object.

Instead of imparting the tracked motion to a new element, a corner-pin tracker distorts the element to fit the tracked rectangular object. Each corner of the new element is moved to the matching corner of the tracked rectangular object.

See Using the CornerPin2D Node on Foundry Learn for more information.

Stabilization

Stabilization uses transform tracking to analyze camera movement and then uses the inverted motion to stabilize the original footage. For example, if you have a hand-held shot with some minor motion, you can use stabilization to make the shot appear static.

When rotoscoping is finished, the motion is added back in. This technique is called reverse stabilization.

See Applying Tracking Data on Foundry Learn for more information.

3D Camera Tracking

3D camera tracking is the most technically complex form of tracking, although it can be easy to apply. It's designed to detect camera motion within a shot and reconstruct the camera's basic properties in 3D space.

This method is a suitable for any shot where the real-world camera is moving along all three axes (X, Y, and Z). For example, if you have a hand-held shot where the cameraman is walking forward, you can use this tracking method to add a new element into the shot, so that the element picks up all the complex movement created by the original camera.

The new element might be a piece of 3D geometry imported from a 3D application such as Maya or 3ds Max, or a "card", which is a 2D layer placed within 3D space.

See Introduction to Camera Tracking from ActionVFX | Nuke Tutorial and Camera Tracking on Foundry Learn for more information.

Planar Tracking

Although planar tracking appears similar to corner-pin tracking, it's much more powerful and can be easier to use. Planar tracking can be done in Nuke and Mocha Pro and tracks a planar feature through space over time. Planar tracking is not concerned with corners or edges, it tracks the entire established feature as if it were fixed to a plane, so it can accurately detect perspective and parallax changes. In fact, the corners of the feature can leave the frame or become temporarily occluded and the tracker continues to work.

Planar tracking also allows you to define the tracked feature by drawing one or more closed spline shapes with an arbitrary number of spline vertices for detailed control.

See Tracking with PlanarTracker on Foundry Learn for more information.

Mesh or GridWarp Tracking

Mesh or GridWarp tracking is a new style of planar tracking available in Mocha Pro and Nuke that is able to track complex organic surfaces. It works by sub-dividing the surface to detect motion for much more detailed control as you can see in the image below.

Mesh tracking can be used to detect the surface deformation of undulating clothes or rippling skin, and in this example, to add skin discoloration that moves naturally with an actor's facial expression.

It can also be used to add a logo to a flapping flag, digital makeup, help out with rotoscoping or to add a matte painting of scars and bruises.

See Warping with GridWarpTracker on Foundry Learn for more information.

You can find the original article by Lee Lanier on the Lowepost website.