DIGITAL COMPOSITING: 2D Motion Tracking
Stock footage can be found here:
STABILISING A SHAKY SHOT
B – Move start of comp work area to timeline indicator N – Move end of comp work area to timeline indicator
1. Double click footage to open it in a separate window. Footage must be tracked in footage view, not Composition view. 2: Open Window > Tracker Controls. Track motion and Stabilise motion collect the same data but use it in different ways. 3: Click stabilise motion and a double square will appear on footage window. Inner square is the tracking area, and outer square is the search area. If search area is too big, track can get inaccurate. Track area should be on a high contrast point, to maintain position frame to frame. 4: Position will be checked automatically, but stabilizing also requires fixing rotation. check that and a second box appears. move this to a point on the same plane as the first. 5: Click the triangular ‘Analyze forward button. It will go through the footage and add a set of keyframes to the footage in a Trackers tab. You can track backwards too, and overlapping isnt a problem – the same data just gets saved again. 6: Click apply – this will bring you back to the composition window, and the footage will be stabilized. 7: This will often show black bars around the edge of the footage, as the footage is offset frame by frame, so the only solution is to scale it up.
1: Layer New Solid to create a layer that will be our new sign. 2: DOUBLE CLICK FOOTAGE TO OPEN FOOTAGE WINDOW 3: Open tracking window and change ‘Track type’ to ‘Perspective Corner Pin’. This will create four linked track points, which should each be placed on the corners of the sign you want to replace.
NB – The search squares dont have to be centred on the track point – the search squares can be on a higher contrat point if its handier, so long as the track point itself is positioned on the corner of the sign being replaced.
4: Click ‘Analyze forward’. We dont want to apply this tracking data to the footage, but instead the solid layer that is our new sign. Click ‘Edit target’ and choose the New sign layer. Click apply.
5: The sign layer will have a ‘corner pin’ effect added to its keyframe timeline, and now be scaled that its corners match the four tracking points.
6: To play with the sign, we will precompose it into a new composition of its own. Click Layer > Pre-compose. In the window, choose ‘Leave attributes in parent comp’. This is important, because the tracking data on the layer must stay in the original parent composition, not the new child composition.
Here you can add text and images to the sign.
7: Back in the parent comp, you can add glows, blurs and colour correction effects etc to match this layer in with the original footage.
TRACKING A POINT ON SCREEN
1: Double click on your footage, to open it in footage view. Open the tracker window and click track motion.
2: Back in your composition, create a new Null object with Layer > Null object. This is just an empty object used for holding data and parenting other layers too. Go back once again to the footage window, and in the tracker controls choose ‘Edit Target’, and select the Null object.
3: The tracking data will be applied to the Null object. Since the Null object doesnt render, we can create a simple text box or text layer to demonstrate it. Draw some text on teh screen. In this layers parent, choose the whip icon and drag it to the null layer. Now when the null moves, the text layer will too.
4: If you want to reposition the text, just move the text layer on screen. Do not adjust the null itself, only the layers parented to it.
5: You can also parent parameters of layers to each other, such as the position keyframe data of the null layer. You can pick-whip one parameter to the other, or just copy and paste the keyframes themselves.
Warp stabiliser is another tool for automatically stabilising shaky shots. It can either be found in newer versions of the tracking menu, or under Animation > VFX Warp Stabiliser
This option appears in newer versions of After effects, and is used for 3D Camera tracking, which will be covered in a later tutorial. Camera tracking is better for large panning shots where the perspective shifts, and for integrating 3D objects. We will cover this later.