Help with shadow catching

[Anonymous]

Hello,

I am working on an animated short. While testing the lighting of the scene I got stuck into a problem. I want to have a shadow catcher for the scene but the "Use Background" material of Maya does not work as well as I would like.

What other alternative would you recommend me to have the shadows extracted for compositing?

I am attaching two images, the first one is how the shadows are supposed to look, the second one is with the Use Background material.

[J450NP13]

That's what you get in the compositing software?  Duplicate it and play with it.

[damaggio]

Use a mental Ray mip-matte shadow node, sorry don't have more info cause I'm on the road, look on the Internet is easy to find, this is a production shader and might be still hidden and you need to enable them.

[slimboJoe]

Do you have some ambient occlusion happening in the top render?  That's won't come out on the "Use Background" geometry.  Plus the shadow on the top image looks crisp and the bottom looks really fuzzy.  May need more info to help.

[Anonymous]

More information regarthing the issue:

Those images are a render straight out of maya no compositing. The render was created using just a physical sun and sky, the only difference between the images is the shader linked to the road. First image has just a plain lambert, second image I just changed the shader to a "Use Background" nothing else.

[Anonymous]

I will take a look at it and see how it works out, thanks!

[J450NP13]

The shawdow should be it's own pass...then composited in so you can adjust. Otherwise just render the beauty pass

[slimboJoe]

I can think of multiple reasons to render the shadow along with everything else exept a BG.

The mental ray matte shadow is the way to go.  Also involved is a ray switching environment node...there are some tutorials online, but I don't have available at the moment.  I just used it recently to render since I needed colored shadows with an alpha channel.  I followed a tutorial online, but I think I had to combine information from several to get the results I wanted.  Sorry, that's not super helpful, but gets you on the right track...

The matte shadow can be used to render separate layer for compositing as well.  It is a less complicated network that way and gives you a lot more control than the Use Background shader.

[damaggio]

Good info Slimbo, I would like to ad also that if he wants no comp, just straight out of render view...that a mib-opacity node needs to be added to the shading network with the matte shadow , wish I had my jpg tutorial but I'm traveling ... If that is what he needs then just try a search with those nodes on Google

[damaggio · Accepted solution]

Here I found mine...

[Anonymous]

Thank you very much for the alternatives and great solutions!

[J450NP13]

Lets see the difference.