Before we get started with the motion tracking, we need a place to store our tracking data. For this, a Null Object will be perfect. You can create a new Null Object by selectingLayer -> New -> Null Object.
I called my layer 'HeadTrack' as we'll be tracking Walter's head
A Null Object is merely a placeholder object with a transform that contains position, rotation and scale data. You can animate these properties or add other custom properties to the Null Object and then use the Null to control other layers in your composition. A Null Object will never be rendered.
We will use the Null Object to store our position and rotation data from motion tracking Walter's head.
Position the track points on the element you want to track. For me, I will place them on the back of Walter's head and on his hairline as I want to track the position and the rotation of his head.Once you positioned your track points, you can start the motion tracking process by clicking on the 'Analyze Forward' button in the Tracker tool window.
After Effects will now, frame by frame, process your footage and try to keep track of the elements you specified with the track points. If at any point in time the track points fail to follow what you expected them to, you can stop this process, go back, reposition the track points and continue the process from where you left of
Sometimes you have to fix a few small things manually or help the motion tracking process along, but eventually you should end up with having your track points follow the object you are tracking nicely.
Now that we have the track points follow Walter's head, we can apply the motion tracking data (position and rotation) to our HeadTrack Null Object. For this, click on 'Edit Target' in the Tracker tool window and select the HeadTrack layer. Then click on 'Apply', select 'X and Y' and click OK.Now when you scroll through your clip, you should see the Null Object follow Walter's head correctly through the shot
You may have to manually fix up parts of the track, for example, where your actor enters or exists the frame. I fixed up the track for the HeadTrack Null Object manually.
Finally, I've created a nice glowing halo effect that we will now attach to Walter's head
Go to any frame in the footage and position the halo nicely over Walter's head.
We now want to parent the halo layer to the Null Object layer. You can do this by selecting the pick whip in the 'Parent' column for the Halo layer and dragging it onto the HeadTrack Null Object. This will make the HeadTrack layer the parent of the Halo layer.
Now, every change in position, rotation and scaling that occurs on the HeadTrack layer will automatically be applied to the Halo layer. Since we used motion tracking to make our HeadTrack Null Object follow Walter's head nicely during the clip, so will our Halo layer
You can add more effect layers and have them follow Walter's head by parenting them to the HeadTrack Null Object. I added a nice glow for the halo to make it look a little more convincing
You can use motion tracking to trace the movement of any element in your footage (as long as they have distinct features you can track), store the data in a Null Object and then use the Null Object to attach effect layers or control all sorts of other effects with itMotion tracking is a fundamental part of knowledge for any visual effects artist and I am sure you will have lots of fun with it!