Digital Compositing - Nuke Tracking #01

Aim: To replace the picture in the frame with another image.

We start by importing the assets into the node graph.

We then attach a 'Tracker' node to the original footage. To start with there will only be one tracker activated on the screen, (fig.1) the inner square indicates the target feature to be tracked, the outer square indicates the area to be searched in the following frame. 

You can then activate up to 3 more trackers per tracker node by ticking the box labeled 'enable' in the node properties panel.

Line up the trackers to the features you want to track. (note that if you are tracking 4 corners the trackers need to be placed on the correct positions: 1=bottom left, 2=bottom right, 3=top right, 4=top left)(fig.2)

to track press the play button in the Tracker node properties panel. 

Now that the track is complete, attach a 'CornerPin' node to the replacement image. We then need to feed the information from the 'tracker' node into the 'cornerpin' node. This is done by Ctrl + LMB-Click-Dragging from the tracked data in the 'tracker' node properties panel to the corresponding parts of the 'cornerpin' node's properties panel. (fig.3) This creates a live link between the two nodes shown by the green pipe.

The 'tracker' node can now be disconnected from the source footage as the data is now stored within the node.

The foreground and background can now be merged. If the image does not match up exactly to the frame (fig.4) a 'transform' node can be applied to the replacement image, where it can be distorted until it fits correctly. (fig.5)

The complete Node Graph is shown in (fig.6) with an additional 'grade' node for basic colour correction.