This page gives some basic details about the Atmosphere render element and how it is used in compositing.
The Atmosphere Render Element stores only atmospheric or volumetric participating media such as fog or Aerial Perspective. This render element can then be used to enhance or color-correct just the atmospheric component of the image during the compositing process.
When atmospheric effects or fog is included in a scene, they render into the Beauty|RGB channel, and should also be output as the VRayAtmosphere channel for compositing use.
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 Atmosphere Render Element is useful for changing the appearance of the atmosphere and volumetric effects in a rendered image using compositing or image editing software. In the example, fog is generated using the VRayEnvironmentFog. A warmer color is assigned to the fog and the intensity is increased using the Atmosphere RE.
The VRayAtmosphere Render Element is Added to the Beauty render to form the final image.