Preventing usebackground shader from receiving reflections from IBL

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  10 October 2012
Preventing usebackground shader from receiving reflections from IBL

Hello CGS.

I'm new to this forum so I hope this is the appropriate place to post this topic. I am also aware that there have been similar threads before, however, I didn't find a solution to my problem.

We have an assignment in school in which we are to model an object (a toaster, in my case) and place it next to its original in a reference photo. We are using IBL and alas, we are not allowed to do any compositing.

Here's my problem: I'm using the usebackground shader, on a plane, for the toaster's shadow and its reflection on the table it stands on. I guess it picks up reflections from the IBL or something because where the plane ends, there's a distinct contrast.

I've tried many different methods but so far to no avail, so I'd be really grateful for any help.

Here's what my scene looks like.

Thank you in advance!
  10 October 2012
well i didnt understant fully, from the image i cant see where the problem is, and for advice and more control i would use mip matte shadow for capturing shadows and reflections,

and for your problem the simplest way of removing any contrast is to extend your plane out of the frame. make sure occlusion in bg shader is to 0 becuase thats for capturing , well occlusion and it will darken your image..

now if you can show the problem area on the render , maybe i can help more
Reel 2014 and RnD
  10 October 2012
Thanks for your reply. Here's a render.

When you talk about occlusion for the useBackground shader, do you mean the setting Occlusion Mask under the mental ray tab? If I slide that to 0, the plane receives no shadows.

A friend mentioned mip matte shadow as an alternative to useBackground - any opinions on that?
  10 October 2012
that looks to me like a specular. does this go away when you zero the specular or reflection.

Mip matte shadow is much more useful than bg shader but in your situation without compositioning it would be still difficult to get what you need
Reel 2014 and RnD

Last edited by tozger : 10 October 2012 at 07:41 PM.
  10 October 2012
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