AUGUST 04, 2003
AE6 Overview Part 1: Tracking and Stabilizing Motion
Tracking Region Indicators
When you have made a selection to either motion track or stabilize footage, the video portion of the Layer window will include a single or multiple tracking region indicators. The tracking indicator is made up of two boxes (one inside the other), which represent the regions After Effects 6.0 will use to track pixels in the footage. The innermost box is the Feature region and is used to define the area or element you want to track in your motion video(the corner of a building or a window, for example).[an error occurred while processing this directive]
The outer box is the Search region. This is used to “limit” the area After Effects uses to find the tracked item inside the Feature region.
If there is just a slight drift, then the box can be smaller. It should be noted that tracking times will increase the larger the search area.
Each of these tracking/stabilization boxes can be resized independently of one another so each contains the necessary regions needed to obtain a perfect track. My suggestion is to size the Feature region box first, as it will adjust the Search region box automatically should the Feature region box get too large. Then, if needed, further adjust the size of the Search region box to accommodate frame to frame movement.
To change the size of the region boxes, click on one of the corner point handles and drag around the screen. You can constrain the box to a perfect square by clicking on the corner handle, then holding the Shift key down as you drag. If you want to change the position of just want to adjust the position of two sides of the box, hold down the control key.
IMPORTANT: The smaller and more accurately placed the Feature region box is, the faster the analysis of the clip will be.
Also, it is not important that the Search region box be centered around the Feature region box. The Search region box should be positioned so that it is looking ahead to the next frame - searching the area where a tracked pixel will be, instead of where a tracked pixel once was. For example, if the tracked data moves down from one frame to another, the position the Search region so there is more area below the Feature region box.
To reposition either of the region boxes, click on the sides of the box and drag to a new position. This is something new to After Effects 6.0. In previous versions you could click anywhere in either of the boxes to move them independently. In AE6.0 clicking and dragging in the region boxes will move the entire tracker box.
A third portion of the tracking region indicators is the Attach Point (previously known as the Tracking Crosshair). If you are familiar with this from AE5.5, the Tracking Crosshair only appeared when doing Motion Tracking, in the latest incarnation, the Attach Point is available during stabilization as well.
The Attach Point designates where the place of attachment for the target footage. This could be an effect control point, the layer itself, or another layer all together.
For example, if you were tracking a CG butterfly onto a practical flower, you would motion track the original flower footage using single point motion tracking. The Feature and Search region boxes will track an area of the frame (the eye of the flower), while the Attach Point tells After Effects where the CG butterfly should be (the petal). After motion tracking is complete, After Effects 6.0 will apply position keyframes to the CG butterfly layer that correspond to the position of the Attach Point.
Like the Search region box, the Attach Point does not need to be centered inside the Feature region box. It shows up there only as the default. There will be times when the Feature region you are tracking is nowhere near the place where you want an element from another layer to be positioned. To move the Attach Point, simply click the center of the crosshair and move it to a new location.
It is a very good idea to always move the Feature region and Search region boxes first, then position the Attach Point - since the tracking crosshair is “parented” to the Feature region box.
However, if you need to reposition the tracking boxes after positioning the Attach Point (perhaps if you need to correct a tracking point during the process), if you Option-drag (Mac) or Alt-drag (PC), you can move the tracking boxes without affecting the position of the Attach Point.
Related sites: Animation Artist Animation Supplement AV Video Content Mastering Corporate Media News Creative Mac Digital Animators Digital Media Designer Digital Post Production Digital Producer Digital Video Editing The WWUG
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