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  1. #1

    Removing Tracking Markers from Video.

    Tracking on grass or asphalt can be difficult because there often aren't any good objects to use as markers, so you need to place your own. In this video, Laustinart shows one way to remove markers, but it only works well if the camera isn't moving too much. If the camera is walking through the scene you'll need something else. I came up with the following technique that seems to work pretty well.

    For markers, I used golf balls propped up on tees for shooting in the grass, and poker chips on the asphalt. (You can get hollow plastic golf balls at Wallmart pretty cheap. Get white ones. Yellow is too similar to green.) Avoid placing markers near shadows or anything else that might get Copy/Pasted into a wrong spot.

    Start by using Laustinart's technique for creating masks around each tracking marker. Don't forget to parent each mask to its marker.
    In the node editor, the Movie output splits in two, one going to an Alpha Over, the other going to a Translate node which then leads to the Alpha Over.

    Create a Mask node for the mask that you made in the Movie Clip Editor. Give it some blur to make the edges less obvious. Plug the Mask into the Fac socket of the Alpha Over.

    Now you'll need to offset the second image a bit using the Translate node. How much and which direction may depend on your scene. If none of the markers leaves the frame you can probably get by with just using the "X" value. Use just enough that you're sampling an area near the marker, but not getting the marker itself.
    If markers are disappearing off the bottom of your movie, you'll need to add some negative "Y" displacement.


    Here's the node setup for the grass scene...

    Click image for larger version. 

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    And here's the asphalt scene. The only difference is the asphalt scene only Translates in the X direction, while the grass scene uses both X and Y.

    Click image for larger version. 

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    Here's a video. I don't have a decent video camera. I use my still camera which takes crummy video, and then Youtube makes it look even worse.




    I'd love to see what someone can do with an HD video.

    This technique should help improve your camera solutions. You can place the markers in an orderly grid which should help when selecting the Origin, X, and Y axes. After you've got your solution, go into the 3D viewport, go to the Top view and see if these markers are in still in a grid. If not, it probably means your Camera Data is off.
    If you bring a tape measure and measure the distance between markers, you can use that with the Set Scale feature.


    Steve S



  2. #2
    I noticed a little glitch in my initial test. When a marker went off the edge of the frame, the mask just sat there for the rest of the video.




    This can be corrected in the Movie Clip editor by manually extending the tracks far enough off the edge of the frame so that the masks won't be visible. But since you're basically guessing where the marker is, this could affect your camera solution. So just end the tracks at the edge of the frame like normal, do your camera solution, then extend the tracks a few more frames past the edge to make the masks disappear.

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    Steve S



  3. #3
    Do you think you can take markers off a human face? That would be great. Ill try but Im not good with nodes



  4. #4
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    The problem with this is that you get an absolute translation going on as in... if you look closely, the tracking mark locations swivel / change what is actually there... it probably would be more noticeable at HD resolution.

    What i would do is pretty much the same, except doing it in a 3D scene... so once you have a 3D track, at the locator points, putting a plane which covers up the markers... Then, creating an image sequence of a stabilized footage, one center point, one for rotation... then make a loopable 12 or so frame sequence and then assigning this to the plane. this way it will respect what the camera is actually doing, and still looks decent.

    Little bit more complex but for shots which rotate around a lot, its nessessary. If the camera doesnt have this sort of rotation translation then your method works fine

    Yes, this will work for human faces.



  5. #5
    Originally Posted by kazinger View Post
    Do you think you can take markers off a human face? That would be great. Ill try but Im not good with nodes
    It might be doable. I think you'd have to offset in the Y direction because the X distance between markers would change as the head turns from side to side. Even then I think it would be difficult as the markers start to disappear from view as the head moves.

    I went and bought a halfway decent camera (1080p, woohoo!) I went out to film a quick test and I'm working on it now. One mistake I made is that I laid out the golf balls in 2 parallel lines (like runway lights.) The ones off in the distance are so close together that it's difficult to track one without it trying to track the one next to it. Lesson learned. I'll post a vid when I get it finished.


    ETA: Here's a before/after still from the test. I think this will work pretty well in most cases. The golf balls work really well as markers. They only times it lost track was when I need to resize the Pattern setting because the golf ball had gotten larger as it approached the camera.

    Click image for larger version. 

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    Also keep in mind that any 3D elements added to the scene should help distract the viewer away from any minor problems with the marker removal.



    Steve S
    Last edited by Steve S; 06-Sep-13 at 01:23.



  6. #6
    I just have a point and shoot. nikon coolpix L 610 point and shoot but it shoots high res.
    This is my first attempt on a head with the blender camera tracking http://www.youtube.com/watch?v=REL3x1crI2w. I wanted to do a transform head gear. It was to grow from a small device to a big( like in Stargate movie) but did not know how to track without painted dots. I almost got it with voodoo tracker.
    I do see the tracking is not good in my video most track point are on a little wire thing with dots on it taped to her head.
    Edit also shadows seem to be a pain in cycles. That's why there are none I could not get them on a transparent object.



  7. #7
    I'm working on that scene and I'm getting some strange behavior from the masks. When the marker makes a change in direction, the mask lags behind and doesn't remained centered on the marker. Can it be made to remain centered?

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    Also, if two masks overlap they result in a Boolean Intersection. Can they be made to Add to each other?

    Click image for larger version. 

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    ETA: Okay, you can ignore the first part of this post. Apparently my computer was just getting a little groggy. I shut it down to have lunch and now it seems to be working fine. I should probably be doing this on my desktop instead of my laptop. It's better at handling stuff like this.

    But does anyone know about the intersecting masks? That's still a problem. Ideally I should refilm and make sure the markers aren't so close together.


    Steve S
    Last edited by Steve S; 07-Sep-13 at 14:27.



  8. #8
    I went back and reshot with the markers placed farther apart. It works really well. I thought you might be able to see where it's been cloned over, but even knowing where the balls are I can't see it.
    And those bright white dots are soooo much easier to track. I used to get frustrated constantly having to reset after the software lost track of a marker. The only time it lost track on this video is when the marker got near the left edge.



    Steve S



  9. #9
    I decided to add Suzanne to the clip.





    Steve S



  10. #10
    Originally Posted by kazinger View Post
    Do you think you can take markers off a human face? That would be great. Ill try but Im not good with nodes
    Blender Cookie has an excellent tut on this (have to be citizen). It uses the 'inpaint' node to paint in where the trackers are.
    http://cgcookie.com/blender/lessons/...oint-tracking/



  11. #11
    Originally Posted by FloridaJo View Post
    Blender Cookie has an excellent tut on this (have to be citizen).
    Why is there nothing in the Blender Wiki about using this node? I don't know if it would work in this situation since I can't figure out how to use it. The only input socket is for the image.

    On a side note, I came up with a way to avoid using the Bezier curves to make the masks. Do the camera solution and set up the scene in the 3D viewer.

    Select one of the markers in the 3D scene, hit Shift-S and select Cursor to selected. Add a sphere and scale it down to the size you want for the mask. Paint it white and select Shadeless.

    Duplicate the sphere. Select another marker, hit Shift-S, select Cursor to Selected, then select the duplicate Sphere, hit shift-S and select Selected to Cursor.

    Repeat this process for all the markers. You'll need to prerender the mask.

    Steve S
    Last edited by Steve S; 12-Sep-13 at 18:50.



  12. #12
    Member hype's Avatar
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    The inpaint node won't work perfectly for grass. It would fill holes, but not with grass texture, just with smeared color.
    I showed some demos of the inpaint node here:
    http://blenderartists.org/forum/show...=1#post2216468

    Also in my BlenderCookie tutorial I show a technique similar tyo what you are talking about - making circles, making them white shadeless, and attaching them to track points. No need to solve a camera, though. Tracking the markers is enough to do the job. And you wouldn't have to prerender anything.

    You could also use rotoscoping (masking) to create the masks.
    If it's not fun, what's the point?
    http://www.imdb.com/name/nm0448332/



  13. #13
    Member 3pointEdit's Avatar
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    Regarding face dot removal. inpaint would be good but I made a tracking distort effect recently, that stabilises a face then alters it. After which you un stabilise the result. I wonder if the clone would be easier to apply in this stabilised area?
    Cheers, David ___________"awesome in space and other places".
    ________Follow me on twitter @3pointedit
    _____________ Check the blog Blender's VSE or Youtube Channel for tutorials.



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