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Table of Contents

This page provides information on the Smoke color rollout of the Volumetric Options dialog.

Overview


This rollout controls the Diffuse color of the Volumetric Shader. The Smoke Color can be a uniform color, a mixture of colors dragged by the simulation (RGB), a function of any physical channel, or sampled from a texture. It is also affected by lights and shadows cast by objects in the scene.

The diffuse color needs external light to become visible. When using a 3ds Max omni light, it should have Shadows and Atmosphere Shadows enabled, as well as VRayShadow. V-Ray lights work with their default settings.


Parameters





Based on
 | darg – Specifies the source channel that will be used to determine the smoke color. By default, a uniform simple color set by the Constant Color option is used. This could also be a texture map, or read from the cache files - in that case the corresponding grid channel must be present in the cache files and remapped to the internal Volume Grid channels using the 3rd Party Channels Mapping dialog in the Input rollout.

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

? – Opens the help documents.

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

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

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

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

Scattering | noscatter – 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 is the same as if the option is DisabledThe Master Multiplier does not affect the rendering in this mode.
  • Disabled – Disables scattering. The Master Multiplier value can be used to correct the brightness because without light scattering the volume generally renders darker.
  • Approximate – Uses an approximate formula which is faster than Ray-Traced scattering and produces good-looking results. Brighter areas of the volume transfer light farther than dark areas. This option is not supported by the Volumetric Geometry render mode.
  • Approximate+Shadows – Same as Approximate, but also affects the strength of shadows over the scene geometry. This option is not supported by the Volumetric Geometry render mode.

Phase Function  | phase_function – Controls the direction in which the light will scatter inside the volume. Negative values correspond to backward scattering, which mimics a volume made up of solid particles and will produce denser and more detailed looks. Negative values are more suitable for smoke or dust effects. Positive values correspond to forward scattering, which mimics a volume made up of water droplets where light will scatter more. Positive values are suitable for highly scattering volumes such as clouds. The default value of 0 will scatter the light in all directions and create an even and diffuse look. See the Phase Function example below.

Note that values very close to 1.0 or -1.0 will produce very directional scattering that will be invisible from most angles, so such values are not recommended. When rendering with a Phase Function different than 0 and Volume Light Cache is enabled the rendered result will be brighter. The Phase function is ignored when the scattering is set to Approximate or Approximate+Shadows.

Optimize Anisotropic Scattering anisotropic_scattering_optimization – When enabled it can greatly reduce the render times for highly scattering volumes such as clouds. Due to certain assumptions made for the optimizations, the optimized render result might produce different results compared to the exact brute-force anisotropic scattering. The option is ignored when the scattering is set to Approximate or Approximate+Shadows.

Volume Light Cache | lightcache – Enables light caching for each voxel of the grid, which speeds up bucket 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. This option consumes additional memory, so beware of high RAM usage when rendering very large cache files or a large number of copied or instanced volumes.
  7. When rendering in Volumetric Geometry mode, for any of these Render Elements: VRayShadows, VRayRawShadows, VRayGlobalIllumination, VRayRawGlobalIllumination, the Volume Grid Light Cache requires additional memory to produce the correct result. Please be aware that these Render Elements (and most other V-Ray Render Elements except for VRayAtmosphere and VRaySelfIllumination) do not work in Volumetric mode.
  8. This option is ignored when using V-Ray GPU. It is a CPU-only feature that helps speed up Bucket rendering.

Light Cache Speedup | subred – [V-Ray specific] [Valid only when Volume Light Cache is enabled] The higher this option is set, the faster the rendering is, but the lower the quality of the Volume Grid Light Cache. You can increase this parameter and gain render speed as long as you don't start getting dark cubic grid artifacts on the smoke.

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

Own Light Scatter Mult | transfown – [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 Light Scatter Mult | transfext – [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.

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

Color gradient | dcolorx_t, dcolory_t, dcolorx_s, dcolory_s, dcolorx_v, dcolory_v, dcolorx_f, dcolory_f  – When the Based on option is set to a grid channel, this color gradient remaps grid simulation data to render smoke color. The sim data channel is laid out horizontally along the X axis in the color gradient.

Simulation data has different ranges, depending on the solver it came from - Phoenix Smoke usually goes from 0-1; Fuel goes from 0-1; Temperature is in Kelvins, so it goes from 300-2000, or a few thousand; Speed is in Voxels/sec, so it depends on the grid size and resolution, but usually goes from 0 to several hundred. Data from other solvers often differs a lot from Phoenix ranges. The channel data range is highlighted in the gradient with a light-blue range which can change as you scroll the timeline as the temperature in a cache file rises, smoke dissipates, speed changes, etc., so keep in mind that the data range for one frame might not be representative for the entire cache sequence. You can also check the data ranges for the currently loaded cache file under the Frame Info rollout of the Volume Grid.

 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 are 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.



Example: Phase Function with front lighting



Phase Function = -0.5

Phase Function = 0

Phase Function = 0.5

Move the slider to see the example renders.






Phase Function = -0.5 (Backward Scattering) 



Phase Function = 0 (Isotropic Scattering)



Phase Function = 0.5 (Forward Scattering)


The orange arrow represents a ray of light going through the volume and the possible scattering directions for the ray.


 

Example: Phase Function with back lighting



Phase Function = -0.5

Phase Function = 0

Phase Function = 0.5

Move the slider to see the example renders.


 




Phase Function = -0.5 (Backward Scattering) 



Phase Function = 0 (Isotropic Scattering)



Phase Function = 0.5 (Forward Scattering)


The orange arrow represents a ray of light going through the volume and the possible scattering directions for the ray.


Example: Smoke Color Based on Speed


The Smoke Color can be based on any channel present in the cache files. The Speed channel can be used to drive the color of the smoke. It is automatically generated by Phoenix based on the Velocity Grid Channel. In this example, the slowly moving smoke is blue while the fast moving smoke is red to yellow.