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Old 07-31-2013, 11:34 PM   #1
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Composite CG Shadow over Live Action

Hello,
I'm having issues adding my CG shadow over a live action plate shadows. I have a simple scene, a 3d car and its shadow and a live action shot of a beach. The shadows in the sand is where I am having issues. When I add the cg shadow over the plate, I see the bright parts through the shadow. i would like my cg shadow to match real.

Can someone help me with my issue please?

link is a frame of my footage.
http://www67.zippyshare.com/v/53015948/file.html
thanks

-NIK
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Old 08-01-2013, 07:11 PM   #2
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You'll need to create a black and white ( or as high contrast image as possible ) to use has a matte for you cg shadows.

You'll probably want to use a noise filter as well to add a similar texture to the shadow as the sand.
 
Old 08-01-2013, 08:20 PM   #3
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Use your shaodw as a mask for a color correction, tone down the backplate.
 
Old 08-01-2013, 09:07 PM   #4
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at first i would try to lumakey the BG, because you only want to shadow the light areas of your BG.

but be aware it can/will give you some artifacts in the edges of the key and maybe will lead to some double shadowing in these areas.

then use the matte from the keyer as a matte for your shadow pass and this as a mask for a grading tool to bring the light areas of the BG footage to the same color as the real shadow
 
Old 08-02-2013, 01:36 AM   #5
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Thank you all for your response. I've tried the keying method. It works to a centain limit then breakdowns because in HD footage each grain has a bit of shadow. The matte become very grainy. I then tried to blur the matte, then I get really bad edges.
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Old 08-02-2013, 05:30 AM   #6
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Degrain your footage. Try creating the matte from the red channel only, it's usually the one with the least noise(has something to do how footage is recorded).
 
Old 08-02-2013, 10:37 AM   #7
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Here is my solution :

I use the shadow as a matte to cut out a constant with the same color as the shadow. I then merge it over the plate using MIN. This takes any color brighter than the constant color on the plate and replaces it with the constant color. Then, I do it again with it slightly lower mix value, then I use a over to finsh it off. so.... the 2 MINs diffuse the sand colors and the OVER adds the shadow color.

Getting a luma key never worked, it gave some very ugly black egdes.

I attached my nuke file just incase you guys wanna try it out..


thanks


Attached Files
File Type: zip test.zip (2.4 KB, 9 views)
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Old 08-02-2013, 10:37 AM   #8
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