Mental ray problem: no shadows in alpha

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Old 08 August 2014   #1
Mental ray problem: no shadows in alpha

Hi,

I'm new to these forums and also kind of new to maya. I hope im posting this in the right section.

My problem

I'm encountering a problem when trying to get a shadow pass from a render.
I want to integrate objects in a live action scene.



Let's talk about the shadows. As you can see it renders shadows perfectly. I have set this up by using a usebackground shader on a plane which receives the shadows and a point light.

Ok. All set. But now I would like to render it but when I check my render it's alpha the shadows are not there!



Does anyone know why this happens to me? I've looked through the web and couldn't find an answer to this.

Thanks ALOT if you could help me out.

Extra info

Renderer: Mental Ray
Maya: 2014
Shader on plane: usebackground
Segmented shadows: On
shadows: Raytraced shadows
 
Old 08 August 2014   #2
mmm

i never use the old use_background shader material, I know it should work but maybe some adjustment are neded, let me test and i let u know

better use the mip_matteshadow mtl, this is one of the hidden mentalray materials
you need to plug in the background slot a mip_alphacolor node and set it to transparent black
so the alpha is present as black and the shadows catch are white or opaque

so every geometry you need to catch shadows to composite in post NUKE or AE you can use this material
 
Old 08 August 2014   #3
interesting.. thanks for the tip im going to try this
 
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