V-Ray Wrapper material / Matte Surface compositing

Overview

With the current setup, the Reflection, Lighting, and GI contribution of the V-Ray Wrapper material are not stored into the corresponding render elements. Due to this limitation, the final Back To Beauty composition will not match the RGB output from the renderer. This article explains how to get the missing information and match the final composition with the RGB output.

Setting up Render elements and Render Output

In order to get this information, you need to add a VRayBackToBeauty render element to your scene. This automatically adds and composites the necessary render elements in the VFB.

Find out more about the VRayBackToBeauty render element here.

Compositing in VFB2

1. Once you add the Back to Beauty render elements and render the image, the VFB automatically composites the render elements in the correct order and places them into a Back to Beauty folder.
2. Select the Source layer. Use the Create Layer button to add a Folder and name it RGB x Alpha.
   
   
   
   
3. From the Create Layer button add a Render Element and set it to RGB color.
   
   
   
   
4. To isolate the background from the needed Reflection, Lighting and GI, add a new render element inside the folder and set it to AlphaL
   
   
   
   
5. Set the Blending mode to Multiply:
   
   
   
   

6. Subtract the Back to Beauty folder from the RGB x Alpha folder:
   
   
   
   

7. Now, you are left with the information about the GI/reflections on the matte surface, which you can control separately.

The missing contribution for Reflections, Lighting and GI from the V-Ray Wrapper Material, along with the other render elements, can be taken to Photoshop or other compositing software for further tweaking.

Please note that you need to use 32-bit images as output, such as EXR files. The 16-bit images do not contain the necessary information.