+ How to track motion in Adobe After Effects CS3? +In this tutorial we will understand how motion tracking works inside of after effects. Motion trackers tracks pixel location on frame-by-frame basis. You can track the movement of an object and then apply that tracking data to another layer or to an effect control point. Motion tracker can also be used for stabilizing the footage. You can also track multiple objects in the same layer. After Effects Motion Tracker is a flexible tool and used widely.
+ Motion Tracking +
Some examples are listed below.
1. Combining elements filmed separately.
2. Stabilizing the footage to remove hand held camera motion.
3. Stabilizing the footage to hold moving object stationery.
4. Animating effects.
5. Animating a still image to match the motion of action footage.
You prepare your short before shooting to get the best result out of the AE tracker. You should attach high contrast markers in your scene because trackers works great when it track a high contrast region. Set the appropriate numbers of track points in your trackers. You can track many points with one tracker. Try to track a point that is visible in entire shot; it should have contrasting colors from the surrounding areas and a consistent shape throughout the shot. One thing more you have to remember is that automatic tracking is not always perfect, some time you have to manually adjust the track points.
To see this in action, download the footage from link. Footage downloaded from this site can be used in commercial projects and it is absolutely free. Also download the project, link is provided at the end of this tutorial. Double click on Motion Tracking composition is it is not open already. In this footage camera is stationery and pans from left to right. Right click on the composition panel and select Track Motion.
You would immediately notice few changes. AE will open a new layer viewer which appropriate because we are tracking layer not a composition.
At the bottom right corner Tracker Controls panel will be docked and a track point is also added in the layer window.
However after effects has a default workspace for motion tracking. Choose Motion Tracking from workspace menu.
Now have a look at Track point Icon.
Feature region defines the element in the layer to be tracked. While defining feature region make sure that feature region should surround a distinct visual element in the shot.
Search Region will allow you to track the set of pixels defined by feature region against those defined by the search region. Confining search to a small region makes tracking faster and it would be processed easily.
Attach Point defines the place of attachment of the target.
There is one more button in the Trackers Controls called Stabilize Motion. It is used to stabilize the footage like footage short with hand held camera. We will discuss stabilizing motion in next tutorial in detail.
Below that is Motion Source, it is the layer that contains the motion to track. Current track is the active tracker. If you click on the Track Motion button you create more trackers in the layer.
Next is track type menu that defines which tracking mode to use.
Stabilize tracks position, rotation and scale to compensate for the movement in the tracked layer. When you track rotation it creates two track points and produces rotation keyframes for the source layer.
Transform tracks position, rotation and/or scale to apply to another layer.
Parallel Corner Pin tracks skew and rotation but not the perspective.
Perspective Corner Pin tracks skew, rotation and perspective changes in the tracked layer.
Raw tracks position only. Use this option when you don’t want to use apply option. The Edit Target button and the Apply button are not available when you use this option. Click on Options button to rename the tracker. There are other options there that we will discuss later.
Motion Target defines the layer that the tracking data will be applied to. Change the target by clicking the Edit Target button. Then there are four buttons for analyzing one frame forwards, forwards, backward and one frame backward when analyze is in progress these buttons changes to stop button that you can used to stop the analyzing.
Reset restores the feature region, search region and attach points to their default position.
Apply button sends the tracking data, in form of keyframes to the target layer.
Click on the Option button and rename tracker1 as Red Ball. You can also rename the tracker within the timeline.
Drag the track point over the red ball; you would notice that AE magnifies the area underneath the Tracker so that you can easily place the feature point on specific area. Drag the corner yellow boxes to enlarge or shrink the feature or search area.
Once you are happy with the position of the track point. Click on Analyze Forward button; make sure that you are at the beginning of the timeline when you add the track point. AE will track the motion and place a series of keyframes.
Twirl down the Motion Trackers option in timeline. You will see a series of keyframe for Feature Center, Confidence and Attach point properties.
Feature Center defines the position of the center of feature region.
Feature Size defines the width and the height of the feature region.
Search Offset defines the position of the center of the search region relative to the center of feature region.
Search Size defines width and height of the search region.
Attach Point defines position defined to the target layer.
Attach Point offset defines the position of the attach point relative to the center of the feature region.
To add additional track point, select the Tracker Red Ball in the timeline from the Trackers Controls flyout menu, select New Track point.
Now click on the Edit Target button and new windows will popup. Select Bird for the layer and press OK.
Next click on the Apply button and pick X & Y from the apply dimension drop down options. It will copy all the keyframe data from the tracker and apply it to position property of the bird layer. Bird layer will jump right over red ball.
Scrub the Playhead in the timeline and you would see that bird is now locked in to red ball. Change anchor point and scale properties of the Bird layer to place the bird perfectly over the red ball.
Now if you change any tracking data in the tracked layer, you have to reapply it by clicking the apply button. To avoid this you can use an expression. That way you never have to click on the apply button. Delete all the position keyframes of the Bird layer.
Alt click on the stop watch of the Position property for the bird layer and pick whip it to Feature Center of the Red Ball Track point. You have now the power of expression you never have to worry about the Applying the changes.
Now if you jump to 3 seconds in timeline and scrub forward, you would notice that a boat there. We want to track this boat and attach a sign to it. The problem with this boat is that it starts off screen. We will fix that.
Double click on the newEngland layer to open it in layer view. Click on the Track Motion button in the tracker controls to add a brand new tracker. Rename this to boat tracker. Jump to the end of the timeline and place the track point in boat area of the shot.
Now analyze backwards and make sure that make sure that you stop analyzing before track point goes off-screen. Stop around 3.26 seconds.
Before we move ahead let us understand what is the confidence value. If I twirl down the boat tracker I can see that my confidence value is currently 98.6%, you might see a different value on your computer as you might have picked a different set of pixels. What 98.6% means is AE is 98.6% confident of its tracking data. Confidence settings can be found by clicking options button.
If Confidence Is Below Specifies the action to perform when the Confidence property value is below the percentage value that you specify.
Continue Tracking ignores the confidence value. Stop tracking used to stop the motion tracking. Extrapolate Motion is used to estimate the position of the feature region. It will continue tracking motion in the direction it was heading. It is good option when your cam move is linear. Select Adapt Feature to use the original tracked feature until the confidence level falls below the specified threshold.
We will modify our trackers position manually, so we will choose stop tracking and set confidence value to 70%. Since our camera is panning in a uniform way. We can move our search area to another set of pixels and leaving attach point where it is. Now alt + drag the search area on the new set of pixels.
Analyze backward again until boat disappears and stop the tracking. We don’t have to track option to the begging of the shot as boat has already gone out of the frame.
Turn on the Plus Sign layer and repeat the process of linking feature point to position of the layer as we did for Read Ball tracker. Likewise you can control the anchor point and scale of the Plus Sign Layer.
Now if you scrub in the timeline you would notice that plus sign goes off the screen as if it was part of the boat. This wraps up this tutorial. I hope it was informative to those who just started learning tracking in After Effects. In next tutorial we will learn how to stabilize the footage using tracking controls.
+ Download Project +