How to cast shadows on an object and not to another?

[rendermotion]

Hi,
I have a "background" frame and an "object" frame to composite in order to get a full frame. It's part of a fly-trough animation.

I'm using VrayMtlWrapper to catch object's shadows on alpha chanel.
the issue is that the background object will cast shadows on foreground objects. But when I render the objects i get shadows that should'n exist (I've marked those in red).

If I set the vraymtlwrapper to receive gi from himself, I obtain the occlusion but in compositing i'll have a doubled shadow in background.

Then, I need to have only object shadows under direct light.

Can someone help me, please?

Thank you a lot,
Pietro

[marco]

you should fully include the background object that is casting the direct shadows in your matte image. In object.jpg the direct shadow from the background object is visible only on the 3 cilinders and not on the background, that's why it cannot "absorb" your unwanted shadows. Please take a look at matte.jpg; this is how your "object-image" should look like.


Marco