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Cinema 4D: The Shadow Catcher Shader

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Beefdoctor

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In this Cinema 4D Video tutorial we take a look at The Shadow Catcher Shader. Not only can this Shader export our shadows with an alpha channel, it can also export reflections too. I also address a problem in which exporting shadows using the Physical Renderer appears not to work.

 

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Guest TeamZissou

Posted

Thank you for making this, it is exactly what I have been looking for!

 

I seem to have hit a brick wall though and was wondering if you could help at all?

 

 

Here's a basic scene to demonstrate:

 

1.thumb.jpg.9a2267707becf668c4f29192bc983368.jpg

 

I only want to render out the shadows so I added a compositing tag to my model, so far so good:

 

2.thumb.jpg.6b1b250769f508a7afbd1aa727c99356.jpg

 

Of course I now need to hide the plane, so I drop the shadow catcher on it and render it out, as you can see it has worked but I appear to be missing those little contact shadows which I'm guessing were created by Ambient Occlusion?

 

3.thumb.jpg.874da5558b4994207085b23ec6853075.jpg

 

Any ideas where I'm going wrong? I thought it might simply not be possible to achieve but then I spotted this video (jump to 28:20) and they appear to have nailed it. What's confusing here is this video was posted 4 years ago, pre shadow catcher..

 

Thanks for your time

 

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I hope you don't mind an answer from me...

 

First of all, the Shadow Catcher does not include AO, so two alternatives are to either add Global Illumination in Render Settings and do without AO (GI will do basic contact shadows), or render out an AO pass by Adding Ambient Occlusion in Effect and Multipass in Render Settings and when compositing , add the Multipass AO over the Shadow pass using Multiply mode.

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Guest TeamZissou

Posted

Thank you @ABMotion perfect!

I tried GI first but I could hardly see any contact shadows. So I went with AO using Multipass and hey presto!

I noticed that 'shadow' is also a Multipass option, does this produce the same shadow as the shadow catcher just not on a transparent background?

 

Any ideas how they managed to end up with the main shadow + contact shadows on what appears to be one transparent layer in Photoshop in that video I linked to?

 

Thanks again

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You can add Shadow as a Multipass as well and use that in a Composite way with the AO together, both using Multiply mode.

 

I'm not sure they do have them both together on a single layer in that video. It's hard to tell. I do not know of a way, nor do I think it's possible to achieve that anyway. As I said in my first post, the only way I would consider that even possible is to use GI and do without AO. It may be just the difference between their lighting and yours that makes it look like it may have. Your last screenshot without AO (shadow only), looks pretty much all one color gray, so it might be that you need some variance or multiple shadows etc.

 

I would also experiment with Standard Renderer rather than Physical to see if you get more of the result you're after. You can add GI to Standard Renderer.

 

 

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Guest TeamZissou

Posted

1 minute ago, ABMotion said:

You can add Shadow as a Multipass as well and use that in a Composite way with the AO together, both using Multiply mode.

 

I'm not sure they do have them both together on a single layer in that video. It's hard to tell. I do not know of a way, nor do I think it's possible to achieve that anyway. As I said in my first post, the only way I would consider that even possible is to use GI and do without AO. It may be just the difference between their lighting and yours that makes it look like it may have. Your last screenshot without AO (shadow only), looks pretty much all one color gray, so it might be that you need some variance or multiple shadows etc.

 

I would also experiment with Standard Renderer rather than Physical to see if you get more of the result you're after. You can add GI to Standard Renderer.

 

 

Got it! So.. what's the point of the shadow catcher shader then? Is it really just to save you from changing your blending mode to multiply? :confused:

 

Yeah, they appear to have a simple setup, it's just the model, a plane and a physical sky by the looks of it, maybe an additional light. Pretty much all I've got.

I wonder how they ended up with all those contact shadows on a transparent bg?

 

I will keep experimenting! Thanks again for your advice

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There are benefits of the Shadow Catcher in certain circumstances. For instance, it uses the alpha channel for transparency and masking and/or can add Reflections as well. If you have geometry in your scene that you want shadows against, it can cause issues that the shadow catcher can alleviate. In your scenario, as you've realised, there is no huge advantage as such.

 

Here is a quick overview of what it does exactly, rather than a tutorial as such: https://www.cineversity.com/vidplaylist/new_in_cinema_4d_r18/use_shadow_catcher_to_create_alphas_from_shadows_for_easy_compositing

 

Have fun experimenting and learning :)

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Here is an older tutorial that shows the old method for Shadow Catching but importantly some reasoning as to why you need to use it. Thought you might find it interesting:

 

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Guest TeamZissou

Posted

On 10/20/2017 at 1:47 PM, Beefdoctor said:

Well i was about to answer but it appears everything has been taken care of, thanks guys ::):

Hey @Beefdoctor Do you have any ideas how they ended up with a single layer of shadows in that video I linked to above ^

Looks like it has all the shadows, including contact, and it's all on a transparency in PS. I'm guessing with the age of their post this was also pre shadow catcher.

 

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Guest TeamZissou

Posted

On 10/24/2017 at 8:48 PM, Beefdoctor said:

Probably by combining AO with the shadow layer? the video doesn't give us much to go on tbh

Yeah I thought that would be the case but it's on a transparent background and I didn't think that was possible pre shadow catcher?

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