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Use Background (for shadows)


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I'm currently trying to light a scene so that it matches a background plate. I've got a character who is casting a shadow onto the ground, I've got my background image in the scene, and I've modeled a ground plan which I think matches well enough for my purposes. Now all I need to do is figure out how to render the shadows on the plane but not the plane itself. In maya, I just use a "background shader". This causes the shadows on the plane to render but where there are no shadows or reflections the background image renders.

I saw instructions for doing this sometime ago (I thought on a sidefx tutorial), but I can't seem to find the link. I've tried using the shadowmatte texture, but that doesn't really help me because it renders the groundplane as black on top of my background texture.

comph.jpg

In order to see if my shadows match the direction of those around them and follow the ground well, I'd have to render it out, pull it into shake, and composite the layers. Is there anyway to just render the shadows on the plane but not display the plane? Anyone come from Maya and know what I'm talking about? Thanks for any help! I imagine there's an easy way to do it, I just haven't found it yet.

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The use of the Shadow Matte Material for the ground plane is just the right way. Just render out your image with this material asigned to the ground, save it as png or tga and composit it over the background plate in the compositing package of your choice ... et voila...

You can load your background plate in Houdini with the d-key / background to adjust your scene. The background plate will show in the viewport but not in the rendered image.

Hope this short answer helps.

Edited by Lutze
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The use of the Shadow Matte Material for the ground plane is just the right way. Just render out your image with this material asigned to the ground, save it as png or tga and composit it over the background plate in the compositing package of your choice ... et voila...

You can load your background plate in Houdini with the d-key / background to adjust your scene. The background plate will show in the viewport but not in the rendered image.

Hope this short answer helps.

Thanks for the reply. As I mentioned above, I was hoping there was a smarter way to do it because I didn't want to keep jumping between packages to see if my shadows work. For now I'll do it that way until I find a better one.

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Thanks for the reply. As I mentioned above, I was hoping there was a smarter way to do it because I didn't want to keep jumping between packages to see if my shadows work. For now I'll do it that way until I find a better one.

You don´t have to switch between apps to view the result. Only my answer was a bit too short. Just set the Background image with the d-key in the IPR Renderview-Tab and you will see your image with background, shadows and all in the IPR / viewport (updating in realtime).

Sven

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You don´t have to switch between apps to view the result. Only my answer was a bit too short. Just set the Background image with the d-key in the IPR Renderview-Tab and you will see your image with background, shadows and all in the IPR / viewport (updating in realtime).

Sven

That worked like a charm:) Thanks.

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