Hey everyone, just wondering if you have a model that you want to put behind a dirty window. The window is not in front of a green screen, just so you know. It's a live shot in a deserted house with a dirty window, yet we want to place a model rendered out of 3ds Max as a png sequence behind it.
Is that possible?
Any help would be great. By the way, great website and forum. Been a lot of help for a long time. =)
Is the camera moving, or locked down? What's currently behind the window? Is it light or dark?
If it's locked down, you might be able to simply mask out the window and position your 3D render. Duplicate the masked layer, invert the mask (so you get the window only), raise it above the BG plate and CG render in the stack, and change its transfer mode to something like screen.
If the camera is moving, you may be able to track the window (Mocha-AE would be brilliant for this) and repeat as above, or you may have to solve the camera in 3D (such as with SynthEyes or the Foundry's CAMERATRACKER). You'd need to export this 3D data both to your Max camera and your AE camera.
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As Walter suggests, some tracking is in order for a moving camera shot.
As for masking, I think you may get better mileage by generating a luminance matte from the dirt. Then use Levels (Alpha) to finesse the actual amount of transparency and the area of transparency you get.