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Camera Tracker, Green Screen, and a 3D Room

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Sean MortonCamera Tracker, Green Screen, and a 3D Room
by on Jan 5, 2012 at 11:24:51 pm

Hi everyone.

Having a lot of difficulty with attempting the following. I have shot an actor on a green screen with the camera moving around the circumference of the actor. (The actor being stationary in the centre). Green screen has all the appropriate tracking markers. I then ran into trouble with my camera tracker solving. It then went bad to worse.

There was no ground plain to specify since the actor was shot waste up. How do i then determine a better track? What is purpose of set origin and where should i be placing this? If there is no ground plane, what would you do??

When i attempted this i messed with the Camera Parented Null Object too much so that the camera then looked like it was were I shot it. This took way to long. what would you do different?

I then used vanishing point in Photoshop to put in a scene. I imported the file in and added it to my existing green screen actor. Put the precomposed room looked absolutely messed when i brought it in. Is there an easy way to make sure all the axis are correct??

Please Help. I have gone through most of the tutorials and manual on this but none show what to do without a ground plane. Not sure whether using vanishing point was the best option for this as well.

Sean


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Dave LaRondeRe: Camera Tracker, Green Screen, and a 3D Room
by on Jan 5, 2012 at 11:28:16 pm

Did you use 3D matchmove software like Syntheyes to do the track?
Motion trackers built into AE can't do 3D tracking.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Sean MortonRe: Camera Tracker, Green Screen, and a 3D Room
by on Jan 5, 2012 at 11:29:28 pm

I used the foundry camera tracker plugin


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Shawn MillerRe: Camera Tracker, Green Screen, and a 3D Room
by on Jan 6, 2012 at 12:28:12 am

Can you post an example of the clip? It's possible that something in the shot is throwing the track off, or you might not have enough features to get a decent track...

Thanks,

Shawn



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ben g ungurenRe: Camera Tracker, Green Screen, and a 3D Room
by on Jan 6, 2012 at 4:04:53 am

+1 to Shawn. We need to see what you are up against before giving very useful advice.

Ben Unguren
Motion Graphics & Editing
http://www.mostlydocumentary.com


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Tudor "Ted" JelescuRe: Camera Tracker, Green Screen, and a 3D Room
by on Jan 6, 2012 at 8:43:39 am

Camera Tracker usually does a pretty good job in figuring out the camera move without a ground plane. You may need to play around with it and chance the settings to get it to give you a better track.
Also, if the camera goes around the actor, vanishing point may not be your better option (there are some weird issues when bringing that in AE- I think Andrew Kramer has a pretty good tutorial that explains how to fix that). I would create the pieces of the 3d room in PSD as separate planes and then build that space in AE with 3d layers.
I also agree that you may be able to get better feedback if you post something for us to see.

Tudor "Ted" Jelescu
Senior VFX Artist


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Sean MortonRe: Camera Tracker, Green Screen, and a 3D Room
by on Jan 6, 2012 at 5:13:37 pm

Yes i sure did find some weird issues. specifically with orientation and it took forever to get something working. I am trying to work out setting up orientation easy. Parenting a 3d object to one of nulls isn't my problem. It's getting proper perpsective in a 3d room without the perpendicular walls warping.

Where would you place your "origin" in your camera tracker plugin? I tried following the latest red giant piece to no avail. If i were to camera track/greenscreen and create scene with my footage, would it be wise to turn off all those layers (thereby not confusing me) and build the proper 3D room in AE with proper orientation. How would i then match the proper perspective of the camera movement that has already been created.

Any suggestions would be appreciated. I did look at the old Creative Cow video of Aharon Rab... on the problems with vanishing point. It was helpful to point them out and the solutions were helpful but still couldn't fix my vanishing point footage... I will give up on that way of doing things.

Here is the Test Footage and what i intially tried to fix using vanishing point. I also felt that the orientation of the Null was very screwed up from camera tracker. i had to play with the null for hours to try to get the created camera to give me the same orientation as I originally shot. it isn't finished but what i want to try to avoid is the warping of walls while panning.







Thanks for any help Crew!!


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Shawn MillerRe: Camera Tracker, Green Screen, and a 3D Room
by on Jan 6, 2012 at 11:55:51 pm

Hey Sean,

I think the problem is your footage. You don't have enough features distributed throughout the shot. To fix this, you might try putting markers not only on the green screen, but also on some stands (with markers) randomly arranged in the shot. Remember, what the tracker is looking for is parallax shift... or the comparative difference in movement between identifiable features. So, if you have objects close to the camera and objects far away from the camera, the software will have an easier time solving the shot. You might also consider using bigger, smoother movements (like a longer dolly shot)... jerky camera movement can add a sense of realism, but it also makes it harder to get a solution with minimal errors. Lastly, make sure that your subject is omitted from the solution, unless your talent is DEAD STILL (and they never are), you should instruct your software to ignore trackers on people, or anything moving... unless you're doing object tracking and camera tracking at the same time. I hope this all makes sense.

Thanks,

Shawn



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Sean MortonRe: Camera Tracker, Green Screen, and a 3D Room
by on Jan 7, 2012 at 12:25:33 am

I am going to try your suggestions next time. I don't think that what I was trying to do is that unreasonable a shot to work with. (i.e. moving around the subject with some motion) My idea being to make it as realistic an enviornment as possible. The idea of placing additional tracking stands sounds reasonable. Maybe the parallax will be more authentic assuming that the closer trackers will move faster than the rear trackers. However if i am trying to move on axis around the actor those stands will get in the way of that movement.

Any other ideas anyone??

Sean


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Shawn MillerRe: Camera Tracker, Green Screen, and a 3D Room
by on Jan 7, 2012 at 12:18:46 am

Sorry, I meant to post an example. For this shot, I used features on the ground, on the house, on the dumpsters and on everything that isn't moving. This made the track easy...



Thanks,

Shawn



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Sean MortonRe: Camera Tracker, Green Screen, and a 3D Room
by on Jan 7, 2012 at 12:33:57 am

I think a lot of my trouble was working without a ground plane which in that example you had a lot of.

I suppose i could shoot from further away but i wanted a closer shot and i don't want to digitally zoom in so that I lose my resolution.

Anybody else??


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Shawn MillerRe: Camera Tracker, Green Screen, and a 3D Room
by on Jan 7, 2012 at 12:46:21 am

"I think a lot of my trouble was working without a ground plane which in that example you had a lot of."

You don't necessarily need a ground plane, just enough (motion) information for the camera tracker to get a good solution. I think the biggest issue with your shot is that you're trying to get a solve with one plane (behind the actor), and not very much motion. You might be surprised at how much easier one or two c-stands with markers on them can make you life.

Shawn



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Sean MortonRe: Camera Tracker, Green Screen, and a 3D Room
by on Jan 7, 2012 at 12:59:40 am

I am certainly going to try that next time! How would you do it with a closer shot though? I am guessing you are going to say i have to restrict my movement. I suppose i could hang some markers above the actors head so as to not impede the shot.

Do you have another suggestion?

one more thing... how should set origin be used in camera tracker? that really confuses me.

Thanks
Sean


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ben g ungurenRe: Camera Tracker, Green Screen, and a 3D Room
by on Jan 7, 2012 at 2:39:30 am

If you don't see the ground, then you don't really need the solver to know exactly where it is. In that instance, I usually make the origin my point of interest (where I am putting in CG elements, for instance).

But, as others have said, the main difficulty with this shot is the lack of parallax: you need foreground, mid-ground, and background elements. And you only have background.. I use syntheyes, and if someone gave me this shot I would tell them that there may not be enough 3D information to get a good solve, but it might be possible to get a 2D track; that is, to treat the camera as though it were on a tripod. Of course, the shot is handheld, but you don't move it around enough in 3D space to give much confidence for a 3D solution. Really you might get better results doing this in Mocha as a planar track, particularly if you only need to put in a background plate.

I recommend the syntheyes website for good general rules on what makes a track-able shot.

Ben Unguren
Motion Graphics & Editing
http://www.mostlydocumentary.com


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