Render image in Vray with transparent background


I would like to render an image with a transparent background so I can easily set a background image behind it in post-production. In my case, I am looking through two curtain walls until I see the background. Since the glass is an object I cant just use the alpha channel to cut it out afterwards. It seems to have something to do with the environment texture, but if I turn it off I don’t get such good results regarding the light in the image (basically almost everything gets dark). I read something about using channels but I can’t seem to figure it out. See the image attached:

I am new to vray and to rendering in general, so please make it easy for me to follow :wink:

Thanks in advance

Did you save your rendering as PNG? I ask, because the background is transparent per default and I wonder why you don’t get it.

Glass will always be opaque over background. You can use Cryptomatte / Multimatte or Material Random Color elements to select glazing and then Reflections / Specular / Refraction elements to somehow edit the glazing in post production.

I’m not sure there’s an easy solution.

Oh wait, there is.

You can use your background image directly in V-Ray:

(try to set the multiplier around 10)

Glass create a transparent alpha if you enable it at the material. At my example from the V-Ray material library: left default fake_glass and right “Glas tempered” where I enabled color+alpha.