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How do I composite an interactive 3D model in a scene?

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Chase GillmanHow do I composite an interactive 3D model in a scene?
by on Aug 9, 2013 at 8:50:06 pm

Let's say I have a 3D model of a TV. I have motion captured the video and imported the camera into 3Ds Max. I placed the TV in the scene. I export to After Effects. How do I get an actor to walk in front of the TV 3D model? Is it as simple/tedious as creating a mask around the actor walking? Is there no easier way such as making an alpha channel from the original video? I know how to do this using a green screen, but can I do it without? How does Lord of the Rings put Golem in the scene and have Frodo walk in front and behind him? Did they seriously create a mask around Frodo and go frame by frame moving the mask path? I have always wondered and have yet to find an answer on the web. Thank you for any input you could give me.


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Angelo LorenzoRe: How do I composite an interactive 3D model in a scene?
by on Aug 12, 2013 at 6:35:49 am

[Chase Gillman] "How does Lord of the Rings put Golem in the scene and have Frodo walk in front and behind him? Did they seriously create a mask around Frodo and go frame by frame moving the mask path?"

Yes, while there are techniques to avoid keyframing every frame (maximizing keyframe distance by breaking up one large mask into to multiple simple shapes), rotoscope work is tedious and exacting. VFX studios have entire departments dedicated to the process.

[Chase Gillman] " Is there no easier way such as making an alpha channel from the original video? I know how to do this using a green screen, but can I do it without?"

You could try a difference mask if the camera doesn't move. The background shouldn't, within a margin of error to account for video noise, change while any motion of the actor should be picked up readily. Rarely as effective as rotoscoping because difference masking will fail so easily.

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Angelo Lorenzo

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