Shadow catcher reflections

Support Materials and Textures
1

Is there a way to set up a shadow catcher that captures the shadows in reflections without capturing the geometry? See example. Yellow box shows the shadow catcher, and red box shows those shadows in reflections. In the example, the reflections are correct (the HDRI). I could simply not make the catcher transparent, but then the

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geometry reflects.
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I want only the shadows reflected. Not the plane.

In fact, the reflected object only seems to reflect shadows, and not reflections in the shadow catcher. Doh! This is annoying.

EDIT. For the purpose of showing my issue, I haven’t aligned the grid to the BG, so I know the reflected BG is off - that’s NOT the issue.

2

Hi,
looking at your portfolio you are an experienced user so maybe my initial answer could looks basic to you but I think the way to do it is by compositor.
This video could be a very good start to go deeper even if it’s from 4 years ago, don’t know if you already saw it.

3

Thank you. There’s nothing in that to address the issue exactly, but I think I can use some of the techniques to achieve the end result.

i.e.

Render out the shadow pass and the reflection pass of the table top/ground/whatever is catching those shadows and reflections.

Use the rendered image as a texture on a proxy table/floor/whatever using the Window mapping.

Re-render with the reflective objects on that proxy, with shadows and reflections turned off.

That should then get me the reflected shadows and reflections from the “ground” plane.

I’ll have to test when I get a little time. Right now, I’m attempting to move my email server from one VPS to a different one, and it’s giving me a headache getting it to work. No worries, though, I have a month before I kill the old server (as in, stop paying for it), so should have time. Fortunately, I have a domain name and email address that isn’t often used so that I can test with that.

4

Please refer to the video :thinking:

5

But that’s not my problem. I already have the shadows and reflections from the CG objects. What I don’t have is reflections of those shadows and reflections in the CG objects.

6

Maybe i understand you not right, but afaik that is not possible.
A reflected shadow is no longer a shadow ray and cant be catched by a shadowcatcher anymore.

7

Don’t know the level of details and needs of your project but have you thought about make the hdri real? I mean an hdri dome, in this case you don’t need a shadow catcher at all.
This is the first video I found, there are a lot of them:

Others solutions could be some complex projection/camera trick using geonodes but I get a headache just thinking about it :grimacing:

8

I think the quickest way is to make the floor a regular object and project the footage on top of it.
That way you can do a full render of the floor, the shadow and the reflections of all of it in one go.

Otherwise it’s going to be a complex set of sub-renders and comping I guess.

9

I’m getting to that point. It still means rendering the background with shadows and reflections, but no objects visible to the camera, using that as a texture, and then rendering the objects with no shadows or reflections (or maybe just without a ground plane on a transparent background) and then compositing them together.