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Matching live action to cg elements.


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#1 James Steven Beverly

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Posted 26 November 2006 - 10:19 PM

What are some things to remember when shooting and lighting live action footage that you know will have CG elements added to them in post to make the CG elements blend more seemlessly and realistically?
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#2 Zamir Merali

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Posted 26 November 2006 - 10:45 PM

I'm not the most knowledgable in this aspect but I would think that you should make sure that you know where the light sources are coming from, Get pictures of a reflective sphere so that you can create a reflection map in your 3d pacakage. Make sure you record some data for camera tracking (ie, lens, distance from various objects). Also make sure the actors know where the cg element will be placed so they can looks and interact with the correct spot. It would probably help to ask the person who will be doing the compositing what they require as well as having a visual effects supervisor if your budget allows.
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#3 Will Earl

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Posted 27 November 2006 - 01:12 AM

Adding to what Zamir said...

Onset VFX people normally grab a few things to help match CG and LIVE-ACTION elements... camera information, survey data, photo reference and lighting information.

Lighting information is obtained via written notes and diagrams. Reference passes are normally taken of a Diffuse and Reflective lightprobe. The reflective probe gives you a reflection map and the position of the lights. The diffuse probe is used to match intensity and colour of the lights.

The idea behind the diffuse (18% reflectance) probe is to match a CG lit sphere to the lightprobe in the plate. This is normally the first step taken in trying to match lighting between CG and live-action.

You should always light your live-action scene just the same as you would normally light it.
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#4 Mark Allen

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Posted 27 November 2006 - 06:54 AM

What are some things to remember when shooting and lighting live action footage that you know will have CG elements added to them in post to make the CG elements blend more seemlessly and realistically?


If the camera is gong to be moving, make sure there are lots of trackable things in the frame. Doesn't necessarily need to be tracking marks, but things which are consistantly there (not a gleam) and high contrast but relatively small in frame - consult with your fx person on that one, it's a big issue.

get measturement of cg subject from camera.

make sure you record the lense width, fstop and all that good stuff. Get photographs and a map of where the lights are on the set and how strong they are and (if possible) measurements. All this helps the artist to build the basic lighting set up.
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#5 Stuart Brereton

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Posted 27 November 2006 - 11:21 AM

On the shows I've done where there is some CG element, we've recorded the lens, focus and stop, as well as lens height and angle (from horizontal).

Usually, the FX super will also ask us to roll a few seconds with reflective globes in shot so they can mimic lighting.
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