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Old 01-18-2013, 09:56 PM   #1
hikarubr
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How to make the floor invisible but keep the shadows?

I need to make the floor of a scene invisible but keep the shadows on the floor for compositing.

I assumed the way to do it would be with a compositing tag, unchecking "Seen by camera"and keeping "Receive Shadows".

But when I do this the shadows disappear with the floor.

What am I doing wrong? Any suggestions?
 
Old 01-18-2013, 10:46 PM   #2
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Invisible? You mean so like you can see the wall behind your computer monitor? No I did not think so. What effect do you want to achieve? Most likely you want to replace the floor with some other image or color, yes? Place that image or color in the color channel of the floor material, then use a compositing tag with Compositing Background checked. This will likely get you where you want to be.


Invisible! Sheesh. Kids today...
 
Old 01-18-2013, 10:59 PM   #3
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Yes, I mean invisible. I want to see the shadow projected on the floor but not the floor itself.

My first post was pretty clear I think. And there is no need for your condescending tone if you can't help.
 
Old 01-18-2013, 11:29 PM   #4
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I'm sorry. My humor didn't land well. OK. To be more concise... there is nothing visible nor invisible in any CG scene. It is all an illusion. You simply need to create the illusion of invisibility. And for that I gave very detailed help in my first post.
 
Old 01-18-2013, 11:40 PM   #5
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If it's a "transparent" layer you are after, so you can place whatever you want in post, then you need to use a multipass render.
Passes needed would be:
- RGB with floor, shadows and all
- shadow pass only
- object buffer to knock out the floor

Then, when compositing, you'd place the RGB image + inverted floor buffer on the top layer, and the shadow layer underneath in multiply mode. Finally, you can use whatever you need as your base layer, instead of the floor.
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Old 01-18-2013, 11:55 PM   #6
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Thanks for the info Fluffouille, that answers my question.

I know how to render with multipasses, but I assumed I could do it inside Cinema 4d just with the compositing tag in a faster way (I was sure I read somewhere that I could do that).

Thanks for the clarification, I'll use multipass then.

Last edited by hikarubr : 01-20-2013 at 08:52 PM.
 
Old 01-19-2013, 05:10 AM   #7
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Quote:
Originally Posted by hikarubr
Thanks for the info Fluffouille, that answers my question.

I know how to render with multipasses, but I assumed I could do it inside Cinema 4d just with the compositing tag in a faster way (I was sure I ready somewhere that I could do that).

Thanks for the clarification, I'll use multipass then.


You might just try checking "compositing background" in the compositing tag.
 
Old 01-19-2013, 05:14 AM   #8
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hmm
 
Old 01-19-2013, 05:16 AM   #9
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One thing that I know hasn't been mentioned before in this thread, but you could try using the Compositing Background option in the Compositing Tag.
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Old 01-19-2013, 08:11 AM   #10
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The guy wants to swap his floor in post. That said, compositing background is a valid option too, in case it hasn't been mentioned before.
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Old 01-19-2013, 10:07 AM   #11
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what you have probably heard is the old shadow catcher plugin.
not sure if it still works in the latest version but here it is (site says its been tested in r13)
http://www.grafxflow.co.uk/tutorial...n-in-cinema-4d/

downside is it only works on normal light shadows not Gi
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Old 01-20-2013, 08:48 PM   #12
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The guy is looking for a shadow matte/shadow catcher equivalent to what's in max.

Most robust way is to do it in multipass.

You can also make a shadow catcher with cell shader:
tutorial

Doesn't work with Physical render I think (because Sketch and Toon isn't supported).

Best,
Eric
 
Old 01-20-2013, 08:57 PM   #13
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Yes, I want to swap the floor in post in After Effects. Sorry if I wasn't clear in the beginning.

Thanks everyone for the help - the shadow catcher plugin and the technique with cell shader are really interesting.
 
Old 01-25-2013, 01:20 AM   #14
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I've looked into this many times, and the only method that seems to work regardless of light type or render engine is the shadow-only multipass, which is then set to multiply in AE as mentioned above. Forget about getting a transparent image with shadow.

Maxon should get their act together and include a proper shadow catcher.
 
Old 07-15-2013, 07:25 PM   #15
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given fluffouille's workflow above,

is there an alternate way route if using Vray? or are you stuck with setting up an additional render with the standard/phys renderer, and using those shadows?

ML
 
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