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View Full Version : Compositing CG Shadows Over Live Action DV Video Footage


AndyWhiteley
06-14-2006, 07:31 PM
What is the best way to composite CG shadows over DV video in After Effects (and Photoshop)?
I want the CG shadow to effectively blend with the original shadow as it would do in the real world.

Below are two tests.
The first one is an unsuccessful example in Photoshop using multiply.
The second is a more successful test in After Effects using the Background to Luma out the Multiplied CG Shadow Layer,
although this produces an unwanted outline around the shadow.

Am I on the right track with the After Effects technique?

Also see After Effects Forum (sorry for the cross thread)
http://forums.cgsociety.org/showthread.php?t=369575

http://www.andywhiteley.com/cgtalk_files/shadow_test_photoshop.jpg

http://www.andywhiteley.com/cgtalk_files/shadow_test_after_effects.jpg

1armedScissor
06-16-2006, 02:15 AM
It's nice if you can get 2-3 bg plates provided by the DOP. 1 - the bg with the appropriate lighting for the scene and no shadows. 2 - the same bg (identical camera settings and movement via motion control rig if applicable) with the key light source(s) turned off, or blocked out. 3 - if there are real shadows required from either onscreen or offscreen real world objects, the bg plate (same camera...) with shadows from these objects.

Then in compositing you'd use your cg shadow as a matte for the "shadow bg" and composite this over the bg with the scene lighting/or the bg with the scene lighting and actual shadows. Perfect integration (minus of course the contact shadow which can easily and quite realistically be achieved via the use of an ambient occlusion pass).

Otherwise if you only have one bg plate and your cg shadow your second method is much more acceptable than the first. What do you think of the results? Simply multiplying the cg shadow, or color correcting the shadow and then multiplying it over the bg looks terrible in my opinion and screams amateur work.

AndyWhiteley
06-16-2006, 11:45 AM
Thanks for the reply but I don't have a DOP or motion control rig to hand!
Also the shot maybe using a hand held camera and the shadows maybe moving, see example below for the effect I'm after (channel 4 ident).

I agree with you. My first technique looks amaturish, this is why I started this thread.
My second technique is more acceptable but has it's problems.
I need assurance that this technique is the way to go or whether anyone has a more professional method.

http://www.andywhiteley.com/cgtalk_files/channel4_ident.jpg

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06-16-2006, 11:45 AM
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