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  1. 3D & Motion Graphics
  2. Adobe After Effects
Cgi

Replacing Broken and Cracked Wall in a Live Action Footage Using 3D Tracking

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Difficulty:IntermediateLength:ShortLanguages:

1. Importing the Footage

Step 1

Open After Effects.

Step 2

Press Ctrl-N to open Composition Settings window. Create a new composition as Final of 6 second duration and the frame resolution as 720/576.

Step 3

Press Ctrl-I to open the Import File window. The live action footage is in image sequence. Select the first frame, turn on the JPEG Sequence option and click on Open.

Step 4

Drag and drop the image sequence in the timeline. You can see the image sequence as the video in the comp/monitor view.

2. 3D Tracking 

Step 1

With the image sequence layer selected, go to Effect > Perspective > 3D Camera Tracker.

Step 2

As soon as you apply the 3D Camera Tracker effect, the system starts analyzing and solving the footage. You can see the progress in the comp view.

Step 3

Once the tracking is done, you get several track points on the footage. 

Step 4

These track point would help to generate the dummy 3D plane/null for linking and the camera. You need to select at least four points to generate the helping dummy or layer. 

Select four corner track points of the photo frame as shown in the following image.

Step 5

With the four corner points selected, secondary-click the mouse and select Create Solid and Camera

Step 6

You get a 3D solid layer and 3D camera in the timeline. This solid layer is the placeholder and sticks with the footage and follows the camera.

Step 7

With the solid layer selected, go to Effect > Distort > Corner Pin.

Step 8

With the upper left corner pin selected, drag and put it to upper left corner of the photo frame.

Step 9

With the upper right corner pin selected, drag and put it to upper right corner of the photo frame.

Step 10

With the lower left corner pin selected, drag and put it to lower left corner of the photo frame.

Step 11

With the lower right corner pin selected, drag and put it to lower right corner of the photo frame.

Step 12

Due to tracking and the adjustment of the corners of the solid layer, the solid layer keeps the photo frame covered throughout the video.

3. Applying Track Matte

Step 1

Keep the solid layer above the photo frame video layer. With the photo frame video layer selected, go to Track Matte tab and select Alpha Matte option.

Step 2

This action eliminates the rest of the portion of the video but the photo frame throughout the video. There is no need to make any mask or do rotoscopy.

4. Cracks and Broken Wall Compositing

Step 1

I've made a crack image which I'll composite in the scene. I've imported the crack image file in the main comp.

Step 2

Turn on the 3D option of the crack file. Copy the Transform and Corner Pin properties of the solid layer and paste them in the crack layer.

Step 3

Increase the Scale of the crack layer so that it appears from the back of the photo frame layer.

Step 4

Put the photo frame video footage in the background.

Step 5

Change the mode of the crack layer to Multiply. Now the crack looks the part of the footage.

Step 6

Create a new composition. Rename this composition as Broken Wall

Step 7

I have an image of brick wall. I'll import that image in the new Broken Wall composition.

Step 8

With the help of Pen tool, make a small mask around the wall.

Step 9

Import the crack image file in the main comp. Turn on the 3D option of the Broken Wall layer file. Copy the Transform and Corner Pin properties of the solid layer and paste them in the Broken Wall layer.

Step 10

Put the Broken Wall layer above the Crack layer. Increase the Scale of the wall layer so that it appears from the back of the photo frame layer. 

Press the Play button and you will see the crack and the broken wall are perfectly matching with the scene.

The End Result

Conclusion

Track Matte is a great technique in After Effects. It saves huge amount of rotoscopy time. With the help of 3D tracking technique in After Effects, it can work wonders.

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