Hiding mib_lookup_background texture when render?

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  07 July 2012
Hiding mib_lookup_background texture when render?

I can't seem to find the info I'm looking for on the forum so here goes:

I've got a shot in which a butterfly (CG) is flying through a forest (live action footage) and I'm currently using a mib_lookup_background with a file image sequence on the Environment Shader for the camera, so that the butterfly recieves final gather color contribution/bounce, making it blend in better. It's all working fine, except for the stage when I'm about to render this out. I only want the butterfly in the render of course, without the background, and right now I'm getting the texture in the mib_lookup_background in the render, which also shows up in the alpha, making the alpha completely white.

How would I go about to solve this problem?

Posting some screens to make you understand the problem better:


This is how I want the butterfly to look, but be rid of the background:



In other words, this is how I want the render in regards to alpha, so that just the butterfly WITH the effect from the lookup is visible, which it's not in this image:



And I want the alpha to look like this:



I'm at a stand still right now. Any info would be useful. Perhaps use an imageplane with Visible In Refractions/Reflections turned on?
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  07 July 2012
Hey,

Did you try using the Attribute Spread Sheet? Click on the object ( background plane) and open up the spread sheet. Then go into "All" turn visibility off and make sure reflections and refractions is turned on. I think this is what you're trying to get at? Then you can render just the butterfly with the alpha behind it as two separate passes or together.
 
  07 July 2012
Originally Posted by Mattgfx: Hey,

Did you try using the Attribute Spread Sheet? Click on the object ( background plane) and open up the spread sheet. Then go into "All" turn visibility off and make sure reflections and refractions is turned on. I think this is what you're trying to get at? Then you can render just the butterfly with the alpha behind it as two separate passes or together.


The thing with a mib_lookup_background is that there is no plane or background to click. You can't even see it in the viewport, but it shows up when rendering.
The problem is that when plugging in textures to the lookup-nodes, they require a "texture"-node. A "file"-node which you would normally use for a sequence of images won't work.

At this point I'm mimicking the color bleed in comp instead, but I'd still like to get to the bottom of this.

When using the "texture"-node in Maya, as the lookup-node is designed to use, you can even check "writable" to get the effects of the background you plugged in, but not see it in the render / alpha, which is what I want. Only problem is I want an image sequence.
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  07 July 2012
Originally Posted by Lightweight: The thing with a mib_lookup_background is that there is no plane or background to click. You can't even see it in the viewport, but it shows up when rendering.
The problem is that when plugging in textures to the lookup-nodes, they require a "texture"-node. A "file"-node which you would normally use for a sequence of images won't work.

At this point I'm mimicking the color bleed in comp instead, but I'd still like to get to the bottom of this.

When using the "texture"-node in Maya, as the lookup-node is designed to use, you can even check "writable" to get the effects of the background you plugged in, but not see it in the render / alpha, which is what I want. Only problem is I want an image sequence.


In the setting for that lookup_background you cant turn visibility off and keep reflections and refraction on? i know a lot of nodes you can do that.. Has to be a proper way to do it
 
  07 July 2012
Environment shader

Hi Lightweight,

You could apply the mib_lookup_spherical as an environment shader in the shading group of the material/materials you want it to apply to, I believe it wouldn't appear in the background then.

Or slightly more complicated I think you could rayswitch the eye/primary rays to black with the correct alpha. From memory, you would need an mip_rayswitch_environment and an mib_colour_alpha for that. But the above method would keep it simple, depending on how many shaders you had

Hope that helps

James

Last edited by jimjunky : 07 July 2012 at 08:38 AM. Reason: spelling!
 
  08 August 2012
I agree to use a mip_rayswitch, it's probably the simplest route just to add one at the end of your shader network to provide the functionality that you're going for, without knowing specifically where you could add it in.

Either that or use the quadswitch and manipulate the way your mib_lookup_background interacts with every object in your scene and your camera. (But that would be a lot more work, depending on what your scene looks like).
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  08 August 2012
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