Tracking

Tracking lets you follow the motion of up to four points in an image sequence. The resulting motion paths can be used to paste one object onto another moving object, or stabilize a sequence with camera shake or other undesired motion. You can also destabilize a previously stabilized sequence to restore the camera motion.

Can accept an input (RGB(A)).

Can optionally accept a foreground input (RGB(A))

Produces an Output (RGB(A)).

Tracking Workflow Overview:

Generally speaking, using the tracker involves the following basic steps:

From the Mode tab of the Trackers page, make sure the tracking Mode is set to Edit Tracks.
Activate the trackers. By default, one tracker is active, but you can activate up to four. Trackers are activated from their respective tabs on the Trackers page.
Position the trackers in the Fx Viewer.
Start tracking by clicking any of the tracking buttons described below. During the tracking process, keyframes are automatically set for the positions of the track point, the template, and the search area, creating the motion path that you'll use for the tracking effect.
Play back the clip to see whether there are errors in the motion path that you must correct. If there are errors, you can adjust the position of the track point, the template, or the search area, as needed, to correct the error.
When the tracking process is finished, apply the desired effect by setting the tracking Mode to Match Move, Stabilize, or Destabilize.
If you are doing a match move, go to the Transform page and adjust the source points on the foreground image that will be pinned to the track points on the background image.

Tracking Buttons:

These buttons allow you to begin or resume the tracking process. During tracking the image sequence is played back and keyframes are set for the track point, the template, and the search area. When tracking is finished, you can see the effect of match moving, stabilization, or destabilization (switch modes if necessary). If you are satisfied with your tracks, you can lock them to prevent further adjustments.

Track From Start: starts tracking from the beginning of the sequence.

From Current: starts tracking from the current frame.

Step: advances to the next frame while tracking. This is useful for identifying a frame where a tracking error occurs.

Trackers

The options on the tabs of the Trackers page are used to activate your trackers. By default, only one tracker is active. You can activate any of the other three on their respective tabs.

The tracker follows a selected rectangular area of the image from frame to frame to create a motion path. You can track using one to four trackers. Each tracker has a template, search area, and track point.

The Template

The template defines a small region of the image area that will be searched for in the subsequent frames. It is the movement of this small region that determines the movement of the tracker. The tracking system must be able to recognize the template and its motion against its surroundings, so you should choose a region with good contrast and detail where possible.
The Search Area

The search area determines how much of the image will be analyzed when searching for the template area.

Processing time is proportional to the size of the search area, so you should avoid unnecessarily large search areas. A very large search area also increases the chance of a false match with some completely different part of the image. If there is an object moving very fast in a particular direction, instead of enlarging the search area, you may want to move it. This lets the system find the new template position without having to search such a large area.
The Track Point

The track point represents the final position over time. Track point values are used to draw motion paths, and are used in calculating the transformations during match moves and stabilization. By default, the track point is the center of the template. However, you can change this either to edit the final path or to set up an offset between the template and the position.

For the trackers to be visible in the Fx Viewer, you must be editing the Tracking operator, and you must be on the Trackers or Options page of this property editor. You can then position the elements of each tracker as follows.

Click+drag any arm of the track point, or any side of the template or search area to reposition the element individually.
Shift+Click+drag the template to reposition all three elements at once.
Click+drag any resizing handle on either the template or the search area to resize the element.

Mode

Track Mode

Edit Tracks: allows you to generate, view and edit your tracks without applying any effect, like match move or stabilize. This is the mode you should use to generate the initial tracking data.

Match Move: inserts a foreground image (to do this you must activate the foreground image on the Output page). By default, the corners of the image are stuck to the track positions. You can alter how the foreground image is stuck down by using options, such as Scale and Rotate on the Transform page.

Stabilize: The relative motion of the paths between the first and the current frame are reversed in order to stabilize the image.

You can alter how the foreground image is stuck down by using options such as Scale and Rotate in the Transform group.

Destabilize: The Destabilize option puts the track back to the motion previously removed using Stabilize.

You can alter how the foreground image is stuck down by using options such as Scale and Rotate in the Transform group.

Two Point Tracking > Apply Scaling/Apply Rotation

When you are stabilizing with two track points, scaling and rotation are applied to maintain the relative positions of the two points irrespective of the way the image is transformed in order to stabilize it. Deactivating these options turns off the scaling and/or rotation.

Track 1/2/3/4

The options on the Track1, Track2, Track3, and Track4 tabs allow you to activate and set various properties for each tracker.

Enable	Activates the tracker.
Mode	Specifies which color space the tracking algorithm uses. Choose Luma, Red, Green, Blue, RGB, or Alpha.
Locked Track	Locks the track, preventing further modifications. This is good to do once you finalize the motion of each active tracker.
Template Settings	Indicate the dimensions of the template box by providing the position of each of its sides. These settings update automatically when you modify the template box in the FX Viewer. They cannot be adjusted manually, although you can keyframe them to override keys set automatically by the Tracking operator.
Track Point Settings	Indicate the position the track point in X and Y. These settings update automatically when you move the track point in the FX Viewer. They cannot be adjusted manually, although you can keyframe them to override keys set automatically by the Tracking operator.
Search Area Settings	Indicate the dimensions of the search area box by providing the position of each of its sides. These settings update automatically when you modify the search area box in the FX Viewer. They cannot be adjusted manually, although you can keyframe them to override keys set automatically by the Tracking operator.
Reset Current Frame Keys	Removes keyframe data for the current frame.
Clear All Track Data	Removes all of the tracker's keyframe data, allowing you to start from scratch.

Accuracy

Current Frame Error

For each track, this field describes the error between the template that the Tracking operator is searching for and the area it actually finds.

The tracking algorithm compares regions on a pixel-by-pixel basis, calculating all the small differences to produce an overall error value. This error value is more relative than absolute - sometimes the error will be greater than 2 and the track will work correctly however sometimes the error value can be low as 0.1 and the track can go off course.

This information is for reference only. You cannot modify it.

Error Warning Threshold

For each track, this parameter defines the maximum acceptable error.

The Tracking operator takes the defined area then moves into the search area to compare the pixels in the template with those in the image at this frame. All occurrences of small errors are added together to find overall error.

Auto Template Change Threshold

For each track, if the error that is calculated is over this value, the Tracking operator will switch templates at that frame. So instead of following the original template it will follow the new region at the frame where the error became bigger than the threshold.

This function is useful when a template is gradually changing over a sequence of frames, so that the feature is significantly different at the last frame from the first frame. For example when the tracker is following a point that is being rotated.

Area Shift

The Area Shift tab displays a slider pair for each track, allowing you to directly change the position of the track area in the foreground image. In other words, the area covered by the track point's path is shifted by the specified amount in the specified direction. In a Match Move, this distorts the foreground image accordingly.

Transform

The options on the Transform page let you control how the foreground image is manipulated when performing a match move.

When you click the button to open this page, four source point markers appear in the Fx Viewer. Each source point is pinned to an active track point, and is numbered accordingly.

Drag these source points in the Fx viewer and position them on the part of the foreground image that you want to pin to the track points.

Transform

Move X/Y	Translate the foreground image, in X and Y, from the original position.
Origin X/Y	Specify the position of the origin in X and Y. The origin acts as a pivot for scaling and rotation done using the options on this tab.
Scale X/Y	Scale the foreground image about the origin, in X and Y.
Rotate	Rotate the foreground image about the origin, by the specified amount.

Corner

The options on the Corner tab set the perspective transform of the foreground image. Set the perspective by adjusting the X and Y sliders for each corner.

Source Point

The Source Point tab displays a slider pair for each track, allowing you to directly change the source point position in the foreground image. In addition, a numbered cross marker is displayed in the Fx viewer for each active track, which you can drag to directly modify the source point position.

When doing a match move, the Tracking operator sticks source points on the foreground image to the corresponding track-point positions on the background.

To set the source point correctly, you should preview the foreground image in the Fx Viewer while editing the Tracking operator.

Rendering

Opacity	Controls the opacity of the foreground.
Foreground Type	Renders the output image as Non-premultiplied, premultiplied or to suppress a backing color.
Backing Color	Suppress the selected backing color when On Backing Color is selected from the Foreground Type list.
Output Alpha	Choose to output the background image's alpha, the foreground's, or a combination of both.
Resampling	Specifies the method by which the pixel content of the transformed image is calculated. Point is the simplest and fastest method. Bilinear is slower, but better for scaling up. EWA (Elliptic Weighted Average) is slower, but best if scaling down by a large degree. Lanczos is the slowest, but best if previewing the sharpness of the image.
Wrap Transform	When the tracking mode is set to Stabilize. During the stabilization process it is very likely that you will lose some of the image. Activating this option during a one-point stabilization you can prevent this from happening.
Make Cutout	Output the transformed foreground only. During a Match Move, select Make Cutout to output the transformed foreground only. You can then composite this foreground onto a background.

Options

Tracking

Show Points	Displays the track as points.
Show Lines	Displays the track as lines.
Retrack on Process	Allows you to track or retrack while rendering. This option must be active for tracking keyframes to be generated. Clicking the Track From Start, From Current, or Step button automatically activates this option for the duration of the tracking process. After the playback and tracking is complete, the option is deactivated.
Crop When Tracking	Applies the crop region while tracking.
Field Mode	Track by frames or, if you are using field based material, by fields. Frame: tracks an object from frame to frame. Field1: tracks an object in Field 1 mode if using field based material. Field2: tracks an object in Field 2 mode if using field based material.

Output Rect

These options allow you to adjust the size of the image output from the Tracking operator.

Tracking

Apply	When activated, the operator outputs only the area defined by the Output Rect controls.
Output Rect Left/Right/Bottom/Top	Specifies, in pixels, the boundaries of the output rectangle's left, bottom, top and right. Adjusting these values scales the operator's output image to the specified dimensions, and from the corresponding side.

Mask

Controls this operator's Mask Options.

Output

Controls this operator's Output Options.

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