- The "Markers" clip

About this Tutorial

The vertical poles in this shot were used to aid tracking of the 3D camera motion. The goal in this tutorial is to remove them. Playing through the clip, you will see that as the poles move across the background the background behind them is revealed. mokey can thus replace the poles in each frame with the background areas from other frames. To do this it has to track the backgrounds very accurately. Note the significant shearing of the background induced by the camera motion. This would make manual cloning of background regions very difficult and time consuming, because both the position and the distortion of the background areas needs to be matched. The mokey tracker is designed to cope with distortion like this.

Loading

When loading the clip, mask out the black borders of the clip using the following Mask settings: Left 3, Right 3, and Bottom 2.

Selections

Create background selections covering range of motion of poles, and create a selection for each pole. Make sure the pole selections are completely outside the poles. Label the selections Ground 1, Pole 1 etc.

Image 5 - Selections in frame 1

Tracking

Track all selections to the end of the clip. No special settings are required, but ensure that the pole selections are inside their corresponding background selections throughout the clip. If a pole drifts outside a background selection, stop tracking, go back to the frame where the problem started, extend the background selection as necessary are restart tracking.

Removal

Select Pole 2 and remove it in all frames back to the start of the clip. Then select Pole 1 and remove it in all frames to the end of the clip. The job is now almost done. You will probably find that some pixels near the bottom of pole 2 are not removed in the first three frames because they were not revealed as the background drifts slightly downwards through the clip. To paint over these pixels switch on Flood Fill for Pole 2 and redo the removal for Pole 2 in the first three frames.