Compositing CG behind glass/semitransparent objects

[Hugh]

I've never done any shots needing specifically CG behind glass, but in situations where there's glass in front of a green-screen, the reflection can usually be pulled off the greenscreen to ensure that it remains in the final comp.

Through fog can be a pain - needs to be carefully matched to make sure that th CG element is as far into the fog as the live action elements at the same distance are. Depending on the level of interaction needed, fog is often added in the comp itself - this requires quite a bit of rotoscoping, but gives more overall continuity in the effect.

[Steve Green]

OK, cheers Hugh.

It always impresses me how well some comps are done, especially when they're having to comp in rain etc.

- Steve

[Aneks]

It depends on the plate. I prefer layering in things like smoke, fog dust etc. rather than having to pull a key with al this junk blocking the screen. Reflections can generally be luma-keyed off glass and laid back in. Fingerprints, scratches etc of green/blue screen or even black glass. Either key it and grab the flaws that way or try inverting the glass and doing a 50% mix with another frame. (Degain first) Now you can isolate the ares that are just flaws and use these as a matte.


hope this helps

[Steve Green]

Cheers Aneks,

Thanks

Steve

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