TIP: intergrating live action with 3D animation

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Chris B
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Joined: Apr 10 2001

hi

Here's a simple technique I'd like to share that I've used to get round the problem of camera movement matching when wanting to put live action into 3D animated scenes. You do need knowledge and access to 3D modeling software.

1. Create your 3D 'set' to scale.
2. Video your actor/s on a blue or green background. TIP: if filming one person lock the camera at 90degrees to get better final resolution.
3. import your video into your editing package, make a copy of the clip and put them side by side on the timeline. key out the blue on both clips and set one of the clips to display the black/white matte as the output.
4. export each clip actor1.avi (keyed) and actor1mask.avi (keyed and matte output)
5. in your 3D scene create a rectangle plane or thin box (to represent the actor).
6. in the material editor import the actor1.avi as the texture and actor1mask as the opacity.
7 apply the texture to the plane or box in the scene.

limitations: the actor can't walk more than a step or two.
Tip. the plane or box with the texture needs to be rotated to face the 3d camera at all times otherwise the illusion will fail.

matching the lighting as best you can helps.

this technique is suitable for animated 3D shots, static shots should be just a layer of keyed video over your background image.

have fun.

Chris

Chris Boylan - boylanmedia.co.uk
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HMC151 Windows 7 CS5 Production i7 950 3.07 GHz GTX570

RichardB
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Joined: Aug 27 1999

Thats a good tip Chris, it's often called '2 1/2D' and it's very common in 3d compositing: you'll find most 3D packages have an option to set the target rectangle plane to always face the camera so you don't need to rotate it manually.

When you buy stock footage of explosions or individual crowd members, you get the footage and the black and white opacity map to go with it. Takes the hassle of making your own mattes away, but then it is nice to build the whole effect from scratch - and it is original.

Spaceships exploding, or large crowds in amphitheatres or football grounds are done this way.

You can make your actor walk more than a few steps by either having walk on a treadmill (cheesy, but it works), or, panning the camera with him as he walks, then simply just animate the rectangle in the 3D program to match. This is where the auto-face function comes in handy, meaning you can concentrate on the walk cycle and not worry about the camera facing.

PS Don't forget to switch on the 'accept cast shadows' function on the rectangle, to make the most of that 3D foreground action!