Composite CG Shadow over Live Action

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  07 July 2013
Composite CG Shadow over Live Action

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.

  08 August 2013
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.
  08 August 2013
Use your shaodw as a mask for a color correction, tone down the backplate.
  08 August 2013
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
  08 August 2013
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.
  08 August 2013
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).
  08 August 2013
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..


Attached Files
File Type: zip (2.4 KB, 10 views)
  08 August 2013
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