This page gives an overview of the Reflection Render Element and explains how it is used.
The 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 pass and therefore render as black.
The Reflection Render Element is formed by multiplying the Raw Reflection (VRayRawReflection) Render Element by the Reflection Filter (VRayReflectionFilter) Render Element. So while the raw reflection pass gives the full reflection of objects reflecting in the scene, the reflection filter sets how much of that reflection should come through in the composite. The two are multiplied together to create the VRayReflection render element which gives a true representation of the reflection in the scene.
The Reflection Render Element is a key component in the main Beauty Pass.
Since V-Ray Next Update 1, some of the render elements are rendered differently than before. The Lighting render element now contains all direct diffuse illumination and the GI element contains all indirect diffuse illumination. Similarly, all direct reflections of lights now go to the Specular element and all indirect reflections go to the Reflection element.
Previously this behavior depended on the sampling of the lights and not just on the type of the contribution. Some of the direct contributions that should be in the Lighting and Specular elements were written to the GI and Reflection elements instead. In both cases they compose back to Beauty correctly but the different types of contributions are now split between the elements more consistently.
This change makes the elements more consistent but it's also needed for preventing artifacts in these elements with the adaptive dome light (and possibly in the future with other adaptive lights).
The raw elements are affected only when the corresponding normal and filter elements are available, otherwise they're rendered as before. This is because the raw elements have to be derived internally from the corresponding normal elements in order to work with the consistent elements (e.g. VRayRawGlobalIllumination = VRayGlobalIllumination / DiffuseFilter).
There's an option to enable or disable the new behavior in the Global Switches rollout under the V-Ray tab in the Render Setup window. The consistent elements are automatically enabled when the scene contains an adaptive dome light so they don't have artifacts. They are also enabled by default for new scenes. For V-Ray GPU they are always enabled without an option to disable them.
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 – When enabled, the render element appears in the V-Ray Virtual 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.
The Reflection Render Element is useful for changing the appearance of reflective elements after rendering using compositing or image editing software. In the example below, the reflections are brightened using the Reflection RE. Some of the reflections are selected using a Cryptomatte mask and a cool tint is applied to them.