How to render a transparent background but keep the reflections of the window/glass material

[christophe913]

Hi there,

See a simple interior scene of kitchen with windows looking towards outside.
As you can see the background is a simple standard sky.

Now, I want to render this image with a transparent sky/background but the keep the reflections on the windows, because I want to post-edit this picture and put my own background in it.

Possible? (check some render elements channels? I don't know...)


Thanks in advance for all your help!
Kind regards,
Christophe.

[Vizioen]

Set your glass to affect color + alpha in the refraction.

Alternatively instead of a VraySky you can put your background on a plane or dome (depending on the BG), position it like you want behind the glass, with a vraylightmtl (your bg as the color texture) and in the geometry itself disable cast/receive shadows and in vrayproperties disable generate GI. You can then play with the VrayLightMtl multiplier for the desired strength.

[christophe913]

Thanks for your quick reply.
It seems that vraylightmtl is only available in Vray for 3D Max ?
Is there another possible workaround for Vray Sketchup?

Thanks!

[Vizioen]

My mistake, I didn't see I was answering in the Sketchup forum haha. SketchUp has an equivalent though: Emissive - V-Ray 5 for SketchUp - Chaos Help

[christophe913]

Thanks.
So, I put a background-picture in an Emissive material. So, in that way I can indeed play with the illumination strength.
The problem though is that after rendering the background-picture-Emissive material looks blurry (after denoiser has did its job).
Any suggestion how I can fix the blurriness?

(The blurriness was actually the reason why I want to put in the background afterwards, in the pos-editing process in Photoshop)

Thanks!

[manishpaul_simon]

Hi Christophe,

You can add a cryptomatte mask render element and add the background later in photoshop. You will be able to retain the reflections as well.
Just make sure to change the background blending mode to multiply and reduce the opacity.

Alternatively, you can also add a render ID to the material and add the multimatte render element.

I mostly use the cryptomatte mask these days as it assigns colors for different materials correctly.

I would suggest that you try using the composite techniques within the Vray frame buffer to change your background. I will be releasing a tutorial on this soon on my youtube channel
https://www.youtube.com/channel/UCqq...VnFfTNCFZzcMPQ

[christophe913]

Ok thanks for the tips manishpaul_simon . I will search it out!