Understanding volumetric scattering and fog in Redshift for Cinema 4D

Apart from Volume object and volume shader, we also have volumetric scattering and fog, which helps you describe lighting and shadow better in a scene. In this article, let’s dive into it to understand volumetric scattering and fog in Redshift for Cinema 4D.

When you enhance a scene, its space around is very important. It contains small particles of water, dust, ash, etc. And when light travels through this space, it changes based on the composition of these particles. Parts of the lighting get absorbed while the remaining lighting gets scattered around.

The volumetric scattering shader allows the user to describe the lighting properties of this space and, therefore, its effects on lighting.
Using the volumetric scattering shader, it’s possible to render:

• • • • A global fogging effect
      • Volumetric light beams and shadows

If you want to use the Volumetric Scattering effect, go to Create > Environment > Redshift Environment:

Enable

It’s used to toggle the volumetric scattering effect (fog and volumetric lighting) on/off

You can find this option in the Basic tab or just use the green checkmark icon to the right of the Redshift Environment in the Object Manager.

Tint

A global tint for all volumetric lighting effects (this doesn’t include global fog)

Scattering

It defines how strong the volumetric lighting effect should be. Higher values will generate brighter volumetric lighting and vice-versa. If you enable volumetric scattering and you get a completely washed-out-white frame, you might need to reduce this setting significantly.

Attenuation

It controls both the strength of the fog and the amount by which light gets attenuated as it travels through the space with light travelling through. Higher numbers introduce stronger fogging and more light attenuation.

Lighting attenuation only happens for non-infinite lights, but not with Dome lights, the physical sun and infinite lights.

Phase

The “Phase” parameter controls how much the lighting will bounce around inside the space with light travelling through and get scattered. In some ways, this setting is similar to the “Diffuse/Specular” settings of a surface material.

A phase of 0.0 means that the lighting will bounce around more and will appear more diffuse. A phase greater than 0.0 produce what is known as “forward scattering”, and the light there will not bounce around much but visible mostly when travelling toward the camera. On the other hand, negative numbers will produce “backward scattering’ which means that volumetric lighting will mostly be visible as it travels away from the camera.

Below are some forward scattering examples.

Emission Color

This parameter enables fog to be self-illuminating. This is useful when you want the fog to have color and not just be black.

Apply Camera Exposure Compensation

This option is enabled to ensure the emission color will be scaled appropriately so that the user won’t have to use large RGB numbers.

Height

This parameter sets the height of the fog. When height is set to zero, fog is omnipresent.

Horizon Blur

The horizon blur setting allows the height fog’s horizon (where the fog joins the horizon) to be faded out which will smooth out the effect.

Use Transform

If activated, you can control the orientation and location of the fog by moving the Redshift Environment object directly in your view. If deactivated, you can set a starting point and direction for the fog by using the Ground Point and Ground Normal parameters.

Ground Point

If using height fog, this setting determines where the fogging effect starts.

Ground Normal

If using height fog, this setting determines the direction of the fog. Using this setting you can create a ‘wall of fog‘ instead of a ‘blanket of fog’. See example images below.

Camera

It defines how much fogging and volumetric lighting you should apply to rays that hit scene objects.

Reflection

It defines how much fogging and volumetric lighting you should apply to rays that were spawned from reflection.

GI

It defines how much fogging and volumetric lighting should be applied to any GI lighting. Applying volumetric lighting on GI computations can wash out the results, produce noise (especially if strong phase settings are used) and be computationally intensive. That’s why Redshift turns off this contribution by default.

Environment Fog

It defines how much fogging and volumetric lighting should be applied to rays that don’t hit anything and go to infinity.

Enable

The ‘Environment Alpha Replace’ option replaces environment alpha with 1. This is because  alpha pre-multiplied  output can make the volumetric effect disappear in areas where the alpha is not 1 or 0. The example below shows a light volume over a black environment with an alpha of 0. You can clearly see the artifacts caused by disabling the option in the preview window of Softimage, where anti-aliasing produces ‘halos’ of alpha values between 0 and 1. You should only disable this option if you expect to composite and effectively replace the volumetric effect where the environment is.

To enable volumetric lighting for a light, use a Volume value above 0. You can find this setting in the Details tab of the Redshift Light.

Below are the effect of some more volumetric-lighting-related settings.

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Source and images: help.maxon.net