This page gives some basic details about the Raw Reflection render element and how it is used in compositing.
Overview
The Raw Reflection Render Element stores reflection information calculated from the materials' reflection values in the scene. Surfaces with no reflection values set in their materials contain no information in the render element, which means these areas render as black. When the Raw Reflection Render Element is multiplied by the Reflection Filter (VRayReflectionFilter), the Reflection (VRayReflection) Render Element is produced.
VRayRawReflection gives the full reflection of objects reflecting in the scene, while the reflection filter VRayReflectionFilter sets how much of that reflection should come through in the composite. In other words, the filter defines the strength of the reflection, while the raw image defines what is being reflected in the image. When these two elements are multiplied, the true level of reflection is given as the VRayReflection Render Element. By using these component parts of the reflection, you can fine-tune the reflection in your final composite.
Parameters
This render element is enabled through the Render Elements tab of the Render Setup window in 3ds Max and displays its parameters in a rollout at the bottom of the window:
VRayVFB – Enables the render element inside the V-Ray Frame Buffer.
Deep output – Specifies whether to include this render element in deep images.
Color mapping – Applies the color mapping options specified in the Color mapping rollout (Render Setup window > V-Ray tab) to this render element. This option is enabled by default.
Multiplier – Sets the overall intensity of the render element, where 1.0 is the standard multiplier.
Denoise – Specifies whether to denoise this render element.
Common Use
The Raw Reflection Render Element is useful for changing the appearance of reflective scene elements in compositing or image editing software after the scene is rendered. See below how a scene looks before and after post-production. The reflections are reduced by increasing the intensity of the Reflection Filter RE. The result is then multiplied by the Raw Reflection to achieve the full reflections.
Underlying Compositing Equation
VRayRawReflection x VrayReflectionFilter = VRayReflection