Hiding Motion Tracking Markets

Nick Royer

Nick Royer

Well-known member
I dont know much about motion tracking but Im going to need to use it on my next movie. My question is how to hide a motion tracking object (i.e. an orange golf ball on a tree)? The shot will be handheld in a wooded area. Should I just motion track off of part of a tree? If I use the gold ball how do I cover it up in post? Thanks.
 
I don't think a ball would work in the first place because you couldn't track rotation off of it, but I'm not entirely sure. If andrew kramer's tutorials are any indication, tracking off part of the tree should work.
 
Ill do some tests when it gets nicer outside. I meant like nail the ball to a tree in the background though, I'm not tracking the ball, I'm tracking the motion of the camera so I can put in CG planes in the sky above the actors.
 
I realize that, but generally tracking markers are "+"s or a similar shape so the camera can pick up the rotation of the tracking point in the image as the camera rotates. You couldn't do that with a ball.
 
you could just set up 2 balls for a rotation reference. As far as getting rid of the balls themselves, well... just use the motion tracking data you get from them to composite a corrected image of the tree or whatever it is attached to over top of the original footage. In other words, you can erase the ball in photoshop and then track that image ontop of the ball in the real footage.
 
Well the ball is the same concept as the x just 3D in dimension. Basically for 3D motion tracks you can have the ball be there so you can track it no matter the angle. Rotational tracking is done using two points to track any change in motion between them. Planar tracking would work here too using the tree.

Alternatives would include gaff tape x's made on the tree. Or simply finding a point with enough contrast so the program can differentiate when motion occurs. Or run it through MatchMover, that doesn't really need motion tracking points.

In essence, anything can be used to motion track. It depends what you are doing with the shot. If it is a 3D track, you might have a little bit of an issue. 2D tracking, any point you can mark will work.

You would need to paint the object out in one frame and use the tracked data to keep the corrected spot in place.

Matt

IPStudios and VFX
 
It will be a 2D shot, no rotation. I want to do a handheld shot with planes in it, so I need the tracking so that the planes look like they are actually there, and not just imposed over the image (i.e. they go in a straight line while the camera moves). I am planning on just shooting a model airplane on a green screen instead of 3D, because the planes are going to be relatively small in the frame, and it is easier to accomplish than 3D.
 
Well you could alway keep filming and remove the ball and paste a piece of feathered footage over where the ball is.

The only issue I see with what your doing is you need to track something very far in the background if its going to look like it would for planes or they'll move too much. Of course you could add an expression to divide down how much motion is applied like to dive it by 2 or 3. Just my thought.
 
Since you're tracking the ball anyway ... you can use the track to copy some other part of the tree over the tracking marker using the same tracking data.

If you really want to cover it seamlessly ... roto work to paint out the marker frame-by-frame is a common approach.
 
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