CG Jam

Tracking Greenscreen

Tracking Greenscreen

In this lesson we learn how to track greenscreen clips and set up the compositing nodes.


This lesson we focus on Blenders motion tracking tools to track a clip. We’ll be using the same clip as the previous lesson which is entitle “match move test wide.” which you can download from the project link.

hollywood camerawork.

a brief summary of the main steps follows.

  1. Open the Motion tracking workspace and load the clip, pre cache the clip the your computers ram and adjust the aspect ratio via the properties panel. you need to set the x value to 1.5.
  2. Add a marker to one of the X’s in the scene, make sure your marker is on a corner of the X to help minimise slipping.
  3. Track the scene, then check though to make sure the marker has stayed in position and hasn’t jumped around any where.
  4. If the track has jumped, grab the marker an move it back onto its point and re track from where it jumped.
  5. Repeat that step until you have covered the scene with markers. ensure you have markers on the floor and both walls. don’t place any tracks on the girl.
  6. Once you have 20 or so markers tracked through the scene, select them all and open the solve tab. press the solve camera button. if your solve error is higher than 0.5 you will need to refine the settings.
  7. Change the keyframe range to a point in the video where the camera swings around creating parallax motion, then re-solve you may have to adjust these settings a few times before you find the optimal keyframe range.
  8. Open the refine menu and select one of the refine options. I found that refining the K1 K2 and focal length was enough.
  9. once you have a solve of 0.5 or less, click the set up tracking scene button, then set as background and split your window and open up a 3D view and enter camera mode
  10. Select 3 markers from the floor and press the set floor button. pick a single marker in the middle of the floor and press set origin then select a marker close to the origin and use it to set the X or Y axis, depending on how you want to orient your scene.
  11. Select two markers that are on X’s next to each other. the X’s are painted 1 meter apart so you can use this to set the scale of the scene. Dont panic if the cube suddenly seems massive, remember it is 2 blender units high which equates to 2 meters in the real world, so it is supposed to be quite large!
  12. Press alt A to run the clip through to make sure the actress is standing firm on the floor. if not you will need to add a few more trackers to get a stable shot. once the girl is solid save your work and we can move on to the next lesson!

If you haven’t yet done the garbage matting tutorial, you will need to go back and cover that lesson before moving on to the next, as we will be using the results of both lessons to incorporate what we have so far into a 3D scene.

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