Final Cut Motion Tracking Plugins
     

4-Point Pin

 

Lyric's 4-Point Pin is a compositing filter that lets you track the 4 corners of a quadrilateral moving within a clip and then pin another clip within it so that the pinned clip is distorted to fit the quad as it moves and changes shape through the clip.

You use 4-Point Pin to composite new moving features onto an existing clip such that they change shape as features in the clip change, for example to place signs on the sides of trucks or buildings as they move and change perspective through the clip.

4-Point Pin provides several features, including:

  • sub-pixel and center-of-weight motion tracking
  • feature selection on any clip frame
  • interactive, frame-by-frame tracking repair
  • track smoothing
  • pinned clip controls, including
    • overall clip offset
    • individual offset controls for each pinning point
    • independent X & Y scaling, with optional automatic aspect adjustment
    • opacity
    • edge-softening
  • final output can be composite, pinned clip only, or pinned clip traveling matte
 

4-Point Pin has a set of fixed steps you work through to get the final composited image. You select the step you wish to perform in the Step dropdown menu. The steps are:

  1. Select the features to track and set the tracking options
  2. Start the motion track process
  3. When the tracking finishes, check the tracks and optionally repair any tracking errors, including retracking portions of the clip
  4. Select a clip to pin, set pinning parameters and pin the clip based on the generated tracks

Doing things this way lets 4-Point Pin build a record of an entire set of motion tracks, so that it can support things like manual track correction, track smoothing and image preprocessing.

 

In principal, the first 3 steps are similar in all the Lyric Tracking Plugins, except that there are 4 separate features to track in 4-Point Pin. With the following differences in mind, you should refer to the Tracking an Image Feature section for detailed instructions on generating and correcting the motion tracks.

The 4 corner features have separate sets of tracking setup parameters, as shown at left. Each lets you select the feature center, search level and center-of-weight threshold independently. The features are numbered 1 through 4, starting at the top-left corner and going clockwise. The search bounding box for each feature is labeled with the feature's number.

Further, the Repair Track controls used in step 3 have an additional dropdown menu, Repair, that lets you select the feature to repair.

If you use the Retrack from Here repair mode on any of the features, 4-Point Pin will remember what parts of what tracks need to be retracked, and will do them all when step 2 is selected. Again, refer to Tracking an Image Feature for details.

 

When you have created a satisfactory track for each corner feature, select 4. Pin in the Step dropdown menu to complete the pinning. Note that you can go back to the first 3 steps at any time to repair a track or track an alternative feature.

You will see an orange frame appear between the tracking points, representing the destination distortion frame for the clip to be pinned.

Drag a clip or image to pin onto the clip well in the Clip to Pin parameter. It will appear, centered within the destination frame and distorted to match the frame. It will stay within the morphing frame as you move the playhead through the clip. Usually, you pin clips with alpha channels, so that they composite over the clip being tracked.

You can use the other parameters in the 4-Point Pin section to adjust the pinned clip, setting its scale, opacity and edge softness as desired.

The Clip Offset point control allows you to offset the pinned clip from the center of the destination frame and the pinned clip will then follow the frame at this offset in all other frames. The individual Pin Offset point controls let you offset the numbered destination frame corner from its tracked feature center. As you move the Pin Offset points, the destination frame changes shape and the pinned clip is distorted to fit within it. The various offset controls are handy if you have a good features for tracking purposes but they are not exactly at the corner points you desire. See the examples below for details.

The scaling controls operate in 2 modes determined by the Auto Aspect checkbox. With Auto Aspect off, X Scale and Y Scale can be independently adjusted to get the desired size and aspect ratio. When turned on, Auto Aspect attempts to maintain the original aspect ratio of the pinned clip by automatically adjusting the internal Y scale based on the average length and width of the destination frame. In this mode, only the X Scale control has any effect.

Note that clip offset and scaling are relative to the pinned clip's original center, so you might want to adjust this prior to pinning to allow the orientation adjustments you might need. In general, it is best to prepare clips-to-be-pinned such that they are roughly the right size, particularly those from Final Cut generators, to avoid large amounts of scaling within the 4-Point Pin filter.

Smooth Track applies a smoothing filter to help reduce jerkiness in the tracks. You can see the smoothed version of the tracks with the Show Track option enabled.

The visibility of the track traces and the destination frame can be controlled with the checkboxes at the bottom of the filter's control panel. Checking Flip Cursor Color will flip all the display colors to contrasting colors in case they are not visible against the current background.
 

The Show dropdown menu lets you chose how the pinned clip will be shown in the output. Composite places the pinned clip over the clip being tracked. Clip Only hides the clip being tracked and just shows the pinned clip. Clip Mask hides both and outputs the pinned clip's alpha channel, so that it can be used as a traveling matte with the Travel Matte - Alpha Composite Mode in the Final Cut timeline.

You should render the composited clip while still working in the Filter tab to ensure that the recorded tracks are not lost. See the note here about when Final Cut will reset tracks and how to protect your tracks and renderings.

Note also that final renderings in the Pin step will not contain any of the track displays that might be visible in the canvas.

 

Examples

The first examples tracks corner points on the two dam towers and suspends a banner between them.

 
Steps 1, 2 & 3 generated a set of tracks for the four corners points.
The banner to be pinned was created at roughly the right scale to fit the final image.
When first pinned in step 4, the banner turns up centered within the destination frame and distorted to fit.
The banner has been scaled using the X Scale and Y Scale controls and points 1 and 2 have been raised using Pin 1 Offset and Pin 2 Offset.
The final rendering.
 
  In the next example, center-of-weight tracking is employed on features in the dam spillway, which greatly improves tracking accuracy, and the banner is now pinned as a sign on the spillway.
Either dark or light features can be used in center-of-weight tracking. The destination frame is offset substantially from the original features using individual Pin Offset controls and the Clip Offset control is used to set the overall position of the sign with the frame.
The advantage of a 4-point pin are shown here in a reverse angle, with the perspective distortion automatically kept correct.  
   

 

Edge Pixel Stretching

The above examples used pinned clips that had masks and so had transparent edge pixels. If you use a full size image as the pinned clip and scale the clip down, the distortion performed to fit the destination frame may replicate the edge pixels and so you can get edge pixel stretching as in the following example.

To prevent this, you can make the edge pixels transparent by applying a 1-pixel crop in the motion panel to the pin clip before dragging it onto the Clip to Pin well, as shown below.

 
     
 
 

.: Copyright © 2003 Lyric Media :..: Contact Us :..: Software License :.