Exercise: Tracking Camera Motion
Click on the icon for a quick preview of the exercise and the final result.

Download an archive that contains the footage as well as the setups used in this exercise.
Put these files in your Flame system: for example under the /usr/tmp directory.

To learn how to load material into the Flame Library, see the exercise:
“Loading an archive”

Images are subject to copyrights: please read the disclaimer at the end of the tutorials.

The purpose of this exercise is to track moving foreground and apply its motion to a static background. Since the back clip in Action cannot be manipulated, let’s load the background as a layer to which we’ll later add the tracking data extracted from the front.

Start in Batch.
Note: In Flame, you access Batch from the Desktop, under the PROCESSING menu.
1. Drag the Library node to the Batch schematic.
2. Select the Lady_Key and Prison_Back shots and press Load.
3. Set the timeline to a length of 48 frames.
4. Drag an Action node to the schematic.
5. In Action’s media list, make sure the empty media strip is selected and choose Add Input twice.
6. Connect the Prison_Back shot to Action’s back and media1 (front and matte) inputs.
7. Connect the Lady_Key shot to the media 2 input (front and matte).

8. Double-click the Action node to display its properties.
9. Display the Result view F4.
10. If the Lady_Key shot is not visible, create a new image for it (double-click the lower-right thumbnail).

Since we’ve already covered keying in another module, here are broad steps to be used as a reminder. Refer to the Keying module for a detailed Master Keyer workflow.

1. In the Media list, double-click media 2’s Keyer field.
2. Click the color sample and drag from a light to a dark green.
3. Display the matte F3.
4. Adjust the Mix setting.
5. Adjust the Matte sampling by moving the cursor above the image while holding Alt.
6. Select Patch 1 sampling.
7. Ctrl-drag areas you want to force to black.
8. Perform Patch 2 sampling for the white areas if necessary.
9. Display the result F4.

If the edges look grayish, this is probably due to the spill suppression. You can use the edge colour trackball and introduce a color for the edge (such as orange), to make the edges blend in.

The key looks acceptable, but the difference in color between the front and back gives it away. Let’s perform a Front color-correction to match the foreground to the back.

1. In the keyer, Click the CCF button to enter the front Colour Corrector.
2. Press the CC button to toggle to the Colour Warper.
3. Darken the Black point (-0.08 or so).
4. Drag the midtones trackball towards warm brown so it matches the back colour.
5. Exit the Colour Warper.
6. Exit the Master Keyer.

Now let’s track the foreground’s motion and apply it to the static background. Since a typical workflow is usually the other way around, let’s connect the foreground clip as the back where it will serve as a tracking reference.

1. In the Batch Schematic, disconnect the back, and connect the Lady_key shot instead.

2. Display the Result F4.
3. In the Action’s media list, select media 1 (the background) and turn the matte off.
4. Display the Action schematic and select the Prison_Back parent axis.
5. In the Axis menu below Stabilizer, choose Scaling On. This will enable two-point tracking. Since there’s no camera roll in this shot, we don’t need to enable rotation.
6. Click on the Stabilizer menu to access the module.
7. Make sure you’re on the first frame.
8. Position the trackers as in the image below.

9. Press Analyse.
10. Scrub the timeline. If the tracking performed successfully, exit the module.

If a tracker fails at a certain frame, scrub to the last accurate frame, disable Fixed, and analyse again. This will update the tracker’s reference at every frame. You may also need to scale the tracker and reference boxes beforehand. If you are still having trouble with a tracker, press Reset in the lower-right corner and start over.

As you can see, the resulting background layer is offset. Let’s reposition it. Since tracking data has been added to the background layer’s axis, we cannot use this axis to reposition the front without destroying the tracking data. Instead, let’s add an offset axis for this purpose.

1. Make sure Auto Key is off.
2. Display the Action schematic ~.
3. Add an axis between the background layer’s axis and the image. Name it offset_axis.
4. Display the Result view F4.
5. Move the offset axis to re-center the image, and scale it up 110%. Move it to the left to include the door on the right-hand side.

The shot is almost done. To make it look like a more credible interior shot, let’s simulate a shallower depth-of-field by blurring the background.

1. In the media list, alt-drag the X and Y blur values for media 1 (the backplate) to a value of about 7.
2. Next to the blur amount, double-click the Gaussian (G) field to get a better quality blur.

To play back the result, you need to add an output node and process.
3. Add an Output node at the end of the process tree.
4. Adjust the output settings (remember that you can automatically adjust the output format to match the source, by T-clicking the Lady_Key input node in the Batch tree).
5. Press Process.
6. If you want to edit this shot later, make sure to save a batch setup.

If you want to know more about the interface and the functionalities covered in this exercise, watch the following overview:

To continue practicing with the next exercise, click on the following link: