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Alternative to motion tracking...?

Posted: Mon, 16th Jul 2007, 9:47am

Post 1 of 9

petet2

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I know that motion tracking is one of the top requests for an enhancement to the programs and I also guess it is pretty hard to implement so I came up with a possible alternative while working on my current movie.

I was trying to composite a 3D cgi dragon animation (as an image stream) with some hand held location footage (not very wobbly but not tripod solid). The problem was that the area of ground where I needed the dragon placed was pretty indistinct so it was difficult to accurately move the quad for the image stream to follow the movement of the ground. There was a dark rock in the background clip which would have been easy to follow but it was some way away from the dragon and there was no way to correlate the position of the two.

In the same movie I had to composite a broken window tiff file over a clip of a window (to make it look broken!) and that was easier because the window frame formed a clear reference area to follow with the handles of the quad for the tiff image.

So I was thinking what if you could add an anchor point to a superimposition layer to follow an easily recognisable part of the background clip? So for example with the first clip I described above I could draw a small square around the rock and this is on or anchored to the layer with the dragon image stream. Then all I have to do is move the small box to make sure it stays around the rock and the dragon moves in the same way (because the two are anchored together) and so follows the movement within the clip.

Most background clips will usually have some distinct point of reference to follow and this facility would enable to use it to move your superimposed image even when it is away from the area where that quad is placed. It's basically the technique you use with programs such as After Effects but you have to move the tracking square by hand rather than the program doing it for you automatically.

Is that possible? To my non-programmer brain it seems simpler than expecting the program to analyse the motion in the clip (the user's brain does that) - all you need the program to do is link two elements together. Obviosuly the anchor point would have to be visible on the canvas but not appear in the final render.

I hope that makes sense - sorry it's a bit wordy but I wasn't sure how best to describe it. If it isn't clear please ask and I'll try again. I might be able to mock up some pictures to help.
Posted: Mon, 16th Jul 2007, 10:33am

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shadu

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When you do CGI tracking in a moving footage use some add one reference point. I have two trick for you. Use a ping pong ball fluo color or some still camera film case painted in red. They can easily put in some strat├ęgic place in the background and they are easily removable by a little painting in post porb.

Shadu
Posted: Mon, 16th Jul 2007, 11:06am

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petet2

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If I could have had more control over the background I would have used something to help locate the cgi dragon but the background plate was a hillside that was pretty busy with people and I was filming it as if it was deserted apart from my actors. It meant that the shots were snatched as and when (hence handheld and not tripod) and we didn't have the chance to position any guides etc. Good tip tho, thanks.
Posted: Mon, 16th Jul 2007, 5:56pm

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ccirelli

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What you are describing is less "motion tracking" and more "match-moving". You are trying to do is re-create the movement of your actual camera and apply it to your 3D camera (the dragon's "camera" in your 3D application). That would be the "right" way to do it, but in many cases (where there is little movement by your 3D object and your camera is only moving side to side) motion tracking can work.

The best answer I can give you is to pick up a license for SynthEyes:
http://www.ssontech.com/

It is inexpensive (compared to BouJou or MatchMover) and it's extremely versatile. Of course, research it first to make sure SynthEyes works with your 3D package - but it can output to pretty much everything out there. And definitely read up on what match-moving is (vs. motion tracking). If you can get the hang of match-moving it will bring your 3D effects shots to a whole different level of realism.

But your workflow, very basically, would be something like:

1. create tracking data on your existing background footage using SynthEyes

2. export camera data from SynthEyes to your 3D application

3. in your 3D app, set up your scene with the dragon using the camera that contains your tracking data

4. export your dragon sequence from your 3D app with alphas enabled in the proper format (image sequence in a format that can handle alpha channels - tiff, png, etc., or, QuickTime Animation set to "Millions of Colors +")

5. composite your background footage and your newly exported 3D dragon sequence in After Effects, Shake, Combustion, whatever compositing app you use that will work with SynthEyes

Depending on your 3D application (I use Carrara 5 Pro) you can also composite your background plate and your dragon directly in your 3D app and skip Step 5, but then you lose some ability to independently color correct each one.

The other suggestion I would make for FXhome is to get in touch with Russ over at Andersson Technologies and perhaps team up to create an export script for VisionLab. There are other 2D apps (Motion v1 for example) that SynthEyes can export to, so in theory it's possible.

Hope this helps.

Please note I have no affiliation with SsonTech other than being a customer. They have a great, affordable product!

craig

Last edited Mon, 16th Jul 2007, 6:01pm; edited 1 times in total.

Posted: Mon, 16th Jul 2007, 6:00pm

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ccirelli

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petet2 wrote:

The problem was that the area of ground where I needed the dragon placed was pretty indistinct so it was difficult to accurately move the quad for the image stream to follow the movement of the ground. There was a dark rock in the background clip which would have been easy to follow but it was some way away from the dragon and there was no way to correlate the position of the two.
Another side note on this, concerning 2D tracking - you don't need to have your tracking point anywhere near the area where you are placing your 3D object. I did this using Shake on the last shot(s) I worked on, but it is also possible using AE.

For example in this particular shot, I needed to track some bullet hits onto the windshield of a car. Well there were no good tracking points in the middle of the windshield where the bullets hit, so I used the corner of the registration sticker instead which was in the corner of the window.
Posted: Mon, 16th Jul 2007, 6:06pm

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Hybrid-Halo

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What you're suggesting is essentially being able to parent layers to other layers. I think it's a good idea.

-Hybrid.
Posted: Mon, 16th Jul 2007, 6:13pm

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ccirelli

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That's correct, in After Effects. In Shake which is nodal-based, there are no layers, so it's a little different. Easier-different, not harder-different. smile
Posted: Mon, 16th Jul 2007, 6:14pm

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petet2

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ccirelli wrote:


What you are describing is less "motion tracking" and more "match-moving". You are trying to do is re-create the movement of your actual camera and apply it to your 3D camera (the dragon's "camera" in your 3D application). That would be the "right" way to do it, but in many cases (where there is little movement by your 3D object and your camera is only moving side to side) motion tracking can work.
To be honest I'm not trying to be that advanced. I'm just trying to superimpose what is effectively 2D footage rather than trying to match up tracking shots etc. Although I'm trying to do this with a dragon animation it would work equally well if you were trying to superimpose something fixed like a castle onto a shot of a hillside for example.

ccirelli wrote:


Another side note on this, concerning 2D tracking - you don't need to have your tracking point anywhere near the area where you are placing your 3D object. I did this using Shake on the last shot(s) I worked on, but it is also possible using AE.

For example in this particular shot, I needed to track some bullet hits onto the windshield of a car. Well there were no good tracking points in the middle of the windshield where the bullets hit, so I used the corner of the registration sticker instead which was in the corner of the window.
Yes that's the point I was trying to make. If there was a way of making the superimposed quad layer move in tandem with a tracking point I would be fine. I don't know of a way within the FX Home programs to have a tracking point away from the quad handles of the effect you are superimposing.

Obviously with AE the program will track the motion autmatically as well. I'm happy to give up a night or two to do that, I just need a way of having an effective tracking point outside the quad.
Posted: Mon, 16th Jul 2007, 7:12pm

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ccirelli

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petet2 wrote:

To be honest I'm not trying to be that advanced. I'm just trying to superimpose what is effectively 2D footage rather than trying to match up tracking shots etc. Although I'm trying to do this with a dragon animation it would work equally well if you were trying to superimpose something fixed like a castle onto a shot of a hillside for example.
There are two issues here - the movement of your camera, and the movement - if any - of your 3D object. Hard to say if it will be successful in 2D without seeing any footage - or without knowing what you want your final shot to look like. But if you disregard your 3D space, you run the risk of making your shot look pretty fake.

Your best bet next time is to simply lock down your camera if you aren't going to match-move.