This page provides general information about the Smoke Color sub-section of the Rendering tab of the V-Ray Volumetric Grid.

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Overview


This tab controls the diffuse color of the volumetric shader. In general, the diffuse color can be a uniform Constant Color, a function of any loaded channel, or sampled from a texture.

 

Parameters



 

Based on | difSource – The source channel used to determine the smoke color. By default, it is a uniform simple color set by the Constant color option. The other options require the corresponding channel to be present in the cache files and remapped to the internal Volume Grid channels using the 3rd Party Channels Mapping dialog in the Input tab.

Disabled – The smoke color will not be rendered.
Temperature – The smoke color will be based on the values of the Temperature cache channel and can be remapped using the color gradient.
Smoke – The smoke color will be based on the values of the Smoke cache channel and can be remapped using the color gradient.
Speed – The smoke color will be based on the values of the Speed cache channel and can be remapped using the color gradient.
Fuel – The smoke will be based on the values of the Fuel channel.
Texture –  The smoke color will be based on the values of a texture map plugged into the Texture slot.
Constant Color – The smoke color will be the same for the entire volume and will be taken from the Constant Color box.
RGB – The smoke will be based on the values of the RGB channel.

Texture | difTexture – If Based on is set to Texture, this slot specifies which texture to use.

Reset to Defaults  – Resets the settings to their default values.

Modulate | difModulate – When Based on is not set to Texture, the color is multiplied by the texture in the Texture slot.

Constant color | difSimpleColor – If Based on is set to Constant color, this color is used. 

Scattering | difScattering – Controls how the light rays are scattered inside the volume.

Ray-traced (GI only) – Enables physically accurate scattering of light rays. This mode produces the most realistic results but it's the slowest to render. It requires V-Ray with enabled Global Illumination, otherwise, the rendered result would be the same as if the option is DisabledThe Diffuse Multiplier does not affect the rendering in this mode.
Disabled – Disables scattering. The Diffuse Multiplier value can be used to correct the brightness because without light scattering the volume would generally render darker.
Approximate – Uses an approximate formula which is faster than Ray-Traced scattering and produces good-looking results. Brighter areas of the volume would transfer light farther than dark areas. This option is not supported by the Volumetric Geometry render mode in the Rendering tab.
Approximate+Shadows – Same as Approximate, but also affects the strength of shadows over the scene geometry. Approximate+Shadows is not supported by the Volumetric Geometry render mode in the Rendering tab.

Scatter Depth | difScatterDepth – Specifies the maximum depth of the GI rays.

Use Light cache | difLightCache – Enables light caching for each voxel of the grid, which speeds up rendering considerably when the voxel size of the grid is significantly larger than the rendering pixel. If the grid resolution is large enough compared to the rendering resolution, disabling this option speeds up rendering.

  1. This option refers to the internal Volume Grid Light Cache, which is not related to the V-Ray Light Cache.
  2. When using V-Ray Progressive Rendering, this option might slow down rendering startup or the overall render speed. 
  3. This feature might produce artifacts when the smoke is very dense.
  4. This feature might produce artifacts when objects cast shadows through the smoke.
  5. Rendering multiple copies or instances of the Volume Grid node with this option turned on might lead to slow-downs.
  6. When rendering in Volumetric Geometry mode, for any of these Render Elements: [ Shadows ], [ Raw Shadows ], [ Global Illumination ], [ Raw Global Illumination ] , the Volume Grid Light Cache will require additional memory to produce the correct result. Please be aware that these Render Elements (and most other V-Ray Render Elements except for [ Atmosphere ] and [ Self-Illumination ] ) do not work in Volumetric mode.
  7. This option is ignored when using V-Ray GPU. It is a CPU-only feature that helps speed up Bucket rendering.

Light Cache Speedup | difLightCacheSR – Used only when Use Light cache is enabled. Because the smoke renders more slowly than the Diffuse geometry, lowering smoke quality can speed up rendering. This option reduces the light sampling and thus increases the noise.

Own Light Scatter Mult | difOwnLightsBoost – Valid only when Scattering is set to Approximate or Approximate+Shadows. This multiplier determines how far the light travels through the volumetric, based on the distance from the emissive light itself.

External Scatter Mult | difExtLightsBoost – Valid only when Scattering is set to Approximate or Approximate+Shadows. This multiplier determines how far the light from all external light sources travels through the volumetric. Both Scatter Boost parameters don't alter the visual density of the smoke to the camera and only apply to the illumination.

Master Multiplier | difMult – A general multiplier for the diffuse color. It is ignored when the Scattering mode is set to Ray-traced (GI only).

Shadow Strength | difShadowStrength – A multiplier for the opacity of the shadow that the volumetric casts on other objects.

Color gradient – By default, this parameter is inactive when using the Based on: Simple Color setting for photorealistic smoke. If Based on is set to a channel of the Volume Grid such as smoke, the gradient controls how the smoke color is driven by this channel's value. The selected channel's data range is highlighted in light blue.

You can use the following controls in the color gradient:

Double click – Creates a new point or changes an existing one.
Left button drag over a point
– Moves the point. If several points were selected beforehand, they move the same amount.
Left button drag over several points
– Selects several points.
Middle button drag over the background
– Drags the visible area.
Mouse wheel
– Zooms in/out.
Right-click
– Displays a drop-down menu where you can add a point, edit or delete a selected point, and fit the entire gradient into the view. If multiple points are selected, they can be edited simultaneously.