Blackmagic Forum

I am trying to do a simple overlay of a photoshopped sign over an actual sign on video. There is a perspective change so I'm trying the corner tracker. The planar tracker just throws the overlay all over the place with no reference to the actual tracking.

So I'm starting with the sign merged over the background video:


I add the CornerPosition node and match the points to the overlay's 4 corners (not sure why it defaults to a skewed shape?)


I pin the tracker's points where they go over the background. The original box stays (green) which, I'm pretty sure, is at least part of the problem.


I right click the first corner and select Modify With > Tracker Position. This is where it gets particularly weird. When I try to line the tracker up to the corner of the bg video, the Tracker window shows a completely different location of where the tracker is. In this image, you can see that the upper left tracker corner is just south of the upper right point in the video but in the Tracker window, it is in the upper left where it should be. Sometimes the image will be closer to the middle of where it should live over the bg video.

Apparently we can only add 3 images to a post (why??) so I'll continue this in a reply.

OK, so here is what I'm seeing in the Tracker window. You can see that the tracker (upper left corner of the overlay) is on the opposite side of the sign from where it is showing on the Tracker window (circled):


I'm guessing there is a method to reset the layout once everything has been squared up but I'm not seeing that. All of the tutorials I've seen have just shown it working so I'm not sure why there is an exception here.

Any suggestions?

The explanation for what you're seeing in your setup is that the two images aren't the same size.
If you were to merge your sign over a blank background that's the same size of your footage the corner positioner would work as you expect it to.

Modifying a point with a tracker can be useful if you want to attach one thing to a point in your image.
In your scenario I would use the dedicated tracker node, since you can do cornertracking/corner positioning/perspective positioning all in one go. The advantage is that the dedicated tracker node compensates for the difference in image size automatically so there's no need to merge over an empty background first.

so the short version is: for what you're trying to do, use a Tracker node.

Thank you for the reply! I really appreciate it. I've honestly spent more time on this issue than I care to admit.

By tracker do you mean a planar tracker? I've tried that several times with similar results each time. The tracker looks fine and the dots seem to stay with the same point in the sign throughout. But for some reason when I pipe the overlay through the planar adjustment node (I think that's what it's called off the top of my head), the overlay image does this weird exaggerated back and forth perspective movement. I have used planar trackers successfully many times so it's strange that it's just doing this here.

To your first point, do you think it would work if the overlay were the same size / ratio as the video layer? I should be able to photoshop an image file that is mostly alpha. Or would you say that's a tall tree to bark up?

By tracker I meant a regular tracker, where you'd track the corners of your image and then use those tracks to corner position them. But depending on your footage you could definitely do this with a planar track as well, maybe even easier. If you're new at this, it might take some time to get your head around all things Fusion, but - again depending on your footage - eventually you'll be able to set the basic version of this up in about 5 minutes.

If you're using a planar transform node to do the transforming you'll have to deal with the same issues you'be been describing. (i.e. mismatch between original footage size and the size of your replacement sign) You're probably better off doing it straight in the planar tracker node. After you'ver tracked you can change the operation mode to 'corner positioner' and you can just pipe your graphic into the planar tracker tool. Set up the corners and you should be good to go.

As for your last question: that is indeed the issue in your particular setup. If the overlay was the same size, then everything would line up. No need to go into photoshop though. You can either merge your overlay on top of of an empty background (with alpha=0) and you'll get that same result. You can also do it by 'cropping larger' i.e. just add a crop tool after your overlay, set it to the size of the footage you're merging over, check 'keep centered' and you'll get a nice clean copy of your overlay with more space around it. The benefit of using the crop method is that it will not add another intermediate filtering, since it operates on whole pixels only.

Wow, thank you. I'll give these a try tonight!

Fusion has been a blast to learn. I've done all of the tutorials (including the BM ones of course) and they have been very helpful. But with those, everything goes right. So when a weird problem like this "dancing" planar tracker comes up, it takes the insight from experience I don't have to fix it.

EDIT: I ended up learning more about the planar tracker which is awesome. I was tracking this sign which enters and then leaves the screen. The planar tracker would not work at either end. So I (and this is more for history sake in case someone stumbles upon this down the road) deleted the frames where the tracker went wacky. The tracking box I had drawn was then able to be manually moved off the screen so that the tracking worked until the end. I then changed the tracking type to corner pin and it worked perfectly.