Keep reflections in glas and fully transparent background at the same moment?

[Pretty Picture Girl]

Hi,

got a problem with reflections. Maybe someone has a suggestion?

Basically I want the image below (Image 1) but need to get rid of the black background in the areas which show the black "sky"
I'd only want the reflections to show, so that I can drop a background image behind the rendered png image in post production.

I tried the Render Elements Reflections & Refractions, but get the black background even in the Png version. Without this black I could use that to get the reflections

The tricky part is:

I need the reflections in the glass
I need the exterior furniture on the balcony visible
I need only the relections in the sky area

Alpha channel in glas material does not help as it affects the whole window (=I lose the exterior furniture).

I did not set a background image in the environment tab.
Even when I set the background color to white 1 in the environment tab, still results in a "blueish" sky (see image 3). I need transparency & reflections where the sky is blue.
If I set white and 10 I get white as background the sky is white but the reflections are fully absorbed by it.
When I set refraction of the glassmaterial to affect Color & Alpha I lose the balcony to some extent. (see image 4)

As I have many images where I would want to add a background in the sky area, but behind the rendered image with reflections I would appreciate a suggestion where I need to render each image only once and only drop the background behind in post.

Any suggestions?

Thanks!

[Pretty Picture Girl]

To put it in shorter words:

I want my render output to have reflections and refraction on the glass materials, have it show the exterior furniture & balcony to its full extent behind reflections, and have the rendering without any background so I can easely import background image.

[Grigio18]

2 steps:

1)Glass material, in reflection tab, search for "affect channel" , set to color + alpha or all channels. ( maybe you ll need to do the same for the refraction tab)
2) if you have a dome light be sure to deactivate the affect alpha option. save to png or exr to bake the alpha inside the image.

[Pretty Picture Girl]

Hi Grigio,

thanks.Tried that already.

When I set refraction of the glassmaterial to affect Color & Alpha I lose the balcony to some extent. (see image 4)
Basically the balcony elements behind the glass turns semi transparent then.
Still I want to keep those elements completly and have the reflections show up slightly on top of them.

Above the balcony is an area of sky where I only want to have the reflections and nothing else (without the black which it shows in image 1. So that when I drop the background in it shows the background only in this area and behind the glass reflections.

There are no dome lights. Only a Vray sun.

Any other thoughts?

[toniboni]

Hey there,
Just passing by to tell you that this is an issue I've been dealing with ever since. Found some cheesy workarounds (using the reflection pass, etc...) but never really suceeded. It would be so cool to find a solution here!

[Pretty Picture Girl]

Dear Chaos Group, could you please give us some ideas on this? Seems this is interesting to a number of people and we are missing a good solution/efficient workflow on this. Thanks so much.
P.S. Have not back from support either. (Yet!)

[Peter.Chaushev]

As Grigio18 already mentioned, simply set the window material's Reflection and Refraction "Affect channel" options both to "Color and Alpha". If Dome Light is used, disable its "Affect alpha" option.
Additionally, to prevent losing the alpha of objects on the other side of the windows, enable the window material's "Back Side Reflect" option in the Reflection section.

Kind regards,
Peter

[joelly3d]

That was it... reflect on backside is what i didn't do. That fixed her up. Thanks Peter!