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Motion tracking - image/sign

PostPosted: Sun Sep 24, 2023 2:12 pm
by Eddiep
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Hi folks,

I am trying to do a motion track for an image which will act as the front of a desk. I was able to use planar tracker for the background, but no matter what I try to use for the front of the desk the image is warped.

I have tried planar tracker, and tracker.

Also - with planar tracker, I have tried the corner pin, directly from planar tracker and also as its own node.

Please see attached images for reference.

Re: Motion tracking - image/sign

PostPosted: Tue Sep 26, 2023 1:06 am
by Glenn Sakatch
Well, the screen right corner of your desk is warped. you have a perfectly rectangular image that you are trying to track on to a non-perfectly rectangular object.

Your desk cover is not very precise on the edges. Your left edge isn't perfect, but it does go fairly straight down, but your right edge curves in towards the center.

I'm assuming your camera is moving, so you would have to try some manual adjustments.
I think a nice, crisp front panel on the table, with clean contrast built into the corners would have made a corner pin quite easy to do on the shot, rather than a green screen.

Re: Motion tracking - image/sign

PostPosted: Tue Sep 26, 2023 8:12 am
by Eddiep
What do you mean/suggest in terms of "manual adjustments."?

And yes, the camera is moving forward toward the desk.


Glenn Sakatch wrote:Well, the screen right corner of your desk is warped. you have a perfectly rectangular image that you are trying to track on to a non-perfectly rectangular object.

Your desk cover is not very precise on the edges. Your left edge isn't perfect, but it does go fairly straight down, but your right edge curves in towards the center.

I'm assuming your camera is moving, so you would have to try some manual adjustments.
I think a nice, crisp front panel on the table, with clean contrast built into the corners would have made a corner pin quite easy to do on the shot, rather than a green screen.

Re: Motion tracking - image/sign

PostPosted: Tue Sep 26, 2023 11:51 am
by Glenn Sakatch
You can't just think of tracking as a "push the button and walk away" operation. You should always be prepared to do some manual adjustment to the keyframes when the track hits a snag.

Look at your spline editor and see when and where the curve takes a weird turn. Those areas may need to be deleted and redone, or sometimes, just deleted, with the in-betweens being calculated from there.

If the camera move is smooth enough, you may not even need to track the table. Just set start, end and middle keyframes for your shape and see how it looks.

A good track can be done fairly simply in many cases with automated operation.
A great track will quite often take a bit more work, and user intervention.

In your case you may want to try to just track the top 3 or 4 inches of the table, to avoid that right hand side, or the entire height of the tabel, but not the width, and then adjust your final shape after you have some tracking data. But i can certainly see where a simple corner pin is going to be a bit off with what you are starting with.

Re: Motion tracking - image/sign

PostPosted: Tue Sep 26, 2023 12:27 pm
by Hendrik Proosa
It is a bit unclear, in what way is the front of the desk warped. Is it warped on the reference frame? Does it get warped during the motion? If former, then your placement of the element needs fixing, modify your cornerpin to make it not warped. If during motion then issue is in the tracking data itself. Although planar tracker can represent perspective transform, camera move where more and more of tracked area is obscured (if cam pushes closer to table) can introduce warping due to lack of data to properly solve the transform. You have to manually counteract it by animating the cornerpin or track backwards from the most obscured frame, which can sometimes help. Imho getting a solid track with less degrees of freedom is better than a wobbly do-it-all track, so you can try solving for example only translation, rotation and scale, but not perspective, and manually animate cornerpin on top to introduce perpective changes (if it is necessary at all).

Since you have already bothered placing a lot of trackable patterns in the scene you could also do a 3D cam track and place a card at the proper location. Make sure to handle lens distortion if there is any though, as that will either make track less precise and/or cause apparent warping in your element. Ff edge of table curves due to lens distortion but your new element doesn't there will be a dynamic mismatch which changes depending on location in the frame.