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The cloud scene rendered with path lengths of 64 (left) and 256 (right).

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The cloud scene rendered with Multi-Scattering Approx. set to 0 (left) and 1 (right) with default Bleed and Contribution.

MS Approx Bleed

The MS Approx Bleed parameter controls how much light bleeds through a volume. Higher Bleed values allow more light to pass through the volume and light areas that would otherwise be shadowed. As such, the effect of MS Approx Bleed is most visible in shadowed areas of a volume, but it also creates a slight overall brightening effect. You can use the bleed parameter to compensate for the overall loss of brightness caused by lower Max Path Lengths.

The cloud scene rendered with Bleed set to 0.1 (left) and 0.9 (right) with default Contribution.

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The cloud scene rendered with Contribution set to 0.25 (left) and 0.75 (right) with default Bleed.

MS Approx Suggestions

• It can be tricky to find good values of Bleed and Contribution since they are very dependent on each other. One process you can try is to start by setting Multi-Scattering Approx to 1, then alternate increasing Contribution and decreasing Bleed in small steps until you get the correct balance of brightness in the shadowed areas.
• Contribution tends to produce a stronger brightening effect, so it should be adjusted in smaller increments than Bleed.
• At high values, the Contribution parameter becomes very sensitive, so you should adjust it in small increments (0.05 or less) as it gets close to 1.

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The cloud scene rendered without anisotropy (left) and with a forward scattering Primary lobe (right) with Primary Anisotropy set to 0.8 and Blend set to 0.

Adding a backward scattering Secondary lobe recovers most of the detail lost in the forward scattering render but still retains some of the detail in the areas facing the light source.

The cloud scene rendered without anisotropy (left) and with a forward scattering Primary lobe and backward scattering Secondary lobe (right) with Primary Anisotropy set to 0.8, Secondary Anisotropy set to -0.2, and Blend set to 0.2.

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