Window Scenic Alpha

[Streetwise]

I can't seem to get my head around how to go about making a window scenic show up as an alpha render element. Of course you can set the Alpha contribution of the scenic plane to 0, but because there's glass in the window, it doesn't work. And because there's glass in the window, if you fiddle with that (Alpha contribution, or Affect channels Color + Alpha for reflection/refraction, you can pull an alpha of the glass, but then any geometry behind the glass (window panes, other building architecture) disappears as well. So short of hiding the glass material in a window, what should the proper procedure be to pull an alpha of a window scenic where the window has glass in it?

Thanks.

[padre.ayuso]

I can't seem to get my head around how to go about making a window scenic show up as an alpha render element. Of course you can set the Alpha contribution of the scenic plane to 0, but because there's glass in the window, it doesn't work. And because there's glass in the window, if you fiddle with that (Alpha contribution, or Affect channels Color + Alpha for reflection/refraction, you can pull an alpha of the glass, but then any geometry behind the glass (window panes, other building architecture) disappears as well. So short of hiding the glass material in a window, what should the proper procedure be to pull an alpha of a window scenic where the window has glass in it?

Thanks.

I don't get that David. If I pull the Alpha off the scene, any objects which don't have refraction behind the glass remain white on the Alpha Channel. Which means any scenary behind the glass will not be deleted. Perhaps, the IOR of the glass is so crazy that it distorts the image? Not sure, but I don't have that problem... Can you send some screen images, maybe I'll understand and I can try to help out.

[Streetwise]

I don't get that David. If I pull the Alpha off the scene, any objects which don't have refraction behind the glass remain white on the Alpha Channel. Which means any scenary behind the glass will not be deleted. Perhaps, the IOR of the glass is so crazy that it distorts the image? Not sure, but I don't have that problem... Can you send some screen images, maybe I'll understand and I can try to help out.

Here's a screen shot. 1) Window scenic plane with bend modifier. 2) Alpha contribution changed from 1.0 to 0.0 3) Region render 4) Not pictured - When I look at the Alpha render element in the frame buffer, I get pure white. No alpha Glass IOR is locked at 1.6.

Thanks.

[padre.ayuso]

I think I get it. Basically, your image is on a plane, but it is rendering in the scene. Why not make the plane not renderable but to show through refractions/reflections? Maybe that does not work, how about create an Material ID or a Render ID and select that in Photoshop and cut it out? If I'm not wrong, your alpha will only show through a "nothingness" yet the plane is an object so no alpha.

[padre.ayuso]

David,

Try making the plane not visible to camera under Object Properties, perhaps you get enough of the image on the refraction pass and you get your alpha and can composite it afterwards. I'm trying out things on the VRay Object Properties, but I'm not sure how to work this out totally.

alex

[Streetwise]

I've tried that along with excluding the glass refraction from the plane, etc... Nothing seems to work. I don't think it's possible. About the best I can come up with is to use a Render ID for the glass, but it's still not physically accurate.

[Sbrusse]

I don't get what you actually want.
Can you describe what you would like to achieve in stead of enumerating what doesn't work

Cheers

[padre.ayuso]

I don't get what you actually want.
Can you describe what you would like to achieve in stead of enumerating what doesn't work

Cheers

I understand what he wants. He wants an Alpha Channel in the window, yet there is a plane outside the window which is the scenic environment. I have never thought that to be possible, but if anyone has any idea. What he's done is as far as I can get to.

[Streetwise]

I don't get what you actually want.
Can you describe what you would like to achieve in stead of enumerating what doesn't work

Cheers

Yes, I would like the ability to be able to composite a different window scenic, if needed, or the ability to adjust the current scenic in post. As long as there's window glass present, I'm not sure how to go about pulling a clean alpha of just the scenic that's on the plane.

[Morne]

Give the material on the plane an ID or give the plane itself an ID (or the glass in the window, whichever will work). Then use the multimatte element as the "alpha".

If you want stuff behind the glass to be shown, then use the plane with your scenic pic as the ID

[Sbrusse]

Why don't you just render out on black and post the background?

[padre.ayuso]

Why don't you just render out on black and post the background?

I agree with Stan. I usually do that and add the background on post, then put a reflection pass on top of it so that I can get my reflections on the windows, just an idea if that is what you are trying to resolve.

[Streetwise]

Why don't you just render out on black and post the background?

Sounds like that's really the only option. I'll give that a try.

Thanks.