Motion Tracking Markers!

If you are filming a subject against green (or blue) screen and you want to move the camera during the shot, then you will need to place tracking markers into the scene.

In post production, computer software locks on to the tracking markers and uses them to create a camera move on the background image which matches the studio camera move.

When the foreground and background elements are combined to create the final image, it looks as if it's all been shot at the same time and with a single camera move.

How tracking works?

Tracking software picks out reference points within the scene and uses these to interpret how the camera moved when you filmed the backplate. The computer can then replicate an identical camera move around the CGI element so that both parts of the composited scene look like they were filmed at the same time and in the same place. Most scenes will have plenty of naturally occurring reference points such as the edges of a building, windows or a prominent landscape feature. If this is the case with your backplate, then you will not need any additional tracking markers.

If the backplate is relatively featureless or low contrast, then you should place some additional tracking markers into the scene.

Where to place these markers is a matter of experience, so if you're not sure, seek advice from the CGI team. But in general, you will need at least 7 in shot at all times during the move with some in the foreground and some in the middle distance. Make sure that at least 7 markers are in shot throughout the move and be careful that they are not covered by moving objects.

Tracking markers have to stand out from the background so black and white disc markers usually work well, although you might use brightly coloured tennis balls or footballs depending on how far they are from the camera.

Making Tracking Markers!

You can make the black and white disc markers yourself, or download a templates for the internet. Make sure they are large enough to be seen by the camera and either stick them to features in the scene or attach them to a rigid but thin pole stuck into the ground. The tracking markers and any support poles will have to be painted out during the compositing process, so you should try to camouflage the poles as much as possible.