View Full Version : Moving backplates + reflections = confusion :D

06 June 2009, 08:55 PM
Okies, got my brain in a bit of a muddle over something here :drool:

Filmed a backplate.
Made an HDRI.
Matchmoved the backplate.

Now, if I put a test object in the scene, a reflective sphere for example, it's lit properly via the HDRI for now.
How on earth do I get reflections of moving subjects on the sphere IF there are obvious moving subjects in the backplate like people reaching towards the CG sphere or something along those lines.

The typical scenario of a still object in a still backplate is simple enough but when everything starts moving, it gets a little tricky.

06 June 2009, 01:31 AM
There are methods of getting movement in the backplate, but from what I know, an actual "backplate" has no movement.

06 June 2009, 09:58 AM
Is it a moving camera or is the shot locked off?
One way would be to shoot a mirrored ball, either in-plate or with a separate camera, that way you have pretty much every reflection angle covered. The only problem is you don't get HDR information, so blown out highlights need to be faked, or you need to shoot underexposed so none of the highlights clip.

In 1985, Lance Williams was part of a team at the New York Institute of Technology that used reflection mapping in a moving scene with an animated CG element. The piece "Interface" featured a young woman kissing a shiny robot. In reality, she was filmed kissing a 10-inch shiny ball, and the reflection map was taken from the reflection of the ball. To make the animation, the reflection map was applied to the robot, and the robot was composited into the scene to replace the ball.


06 June 2009, 10:32 AM
Hey guys !

I'm glad it sort of made sense :)

The video camera is moving, typical handheld style.
The 'mirrorball' is being used for the HDR, and as many sources suggest, it's in place of the CG element\character.
And, as you've suggested, I could also use another 'locked off' video camera for the world reflection on the mirrorball whilst I wonder around with the camera. In this particular instance, it's actually better if I'm in the reflection as well. :)

Just a bit of extra info:

Software usage is:
Softimage + Mental Ray - So I can use things like their mip_rayswitch_environment, mip_cameramap, mip_mirrorball, mip_matteshadow as suggested in the last pages of the 'production' pdf document =
I'm not using FG or GI, just typical lightdome and other lights.

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06 June 2009, 10:32 AM
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