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titleDiffuse Parameters

Diffuse Parameters

The diffuse parameters control the look of basic diffuse reflection. These are often used to define primary color attributes for opaque objects; wood textures, label text, polka dots, or more, you can find them all connected here. This lobe is on by default.

Gain

Gain is the weight applied to the diffuse parameters. You may also drive this with another pattern to show things like fading or wetness (where liquid darkens a surface). Below are examples at 0.0, 0.5, and 1.0 gain for a 50% grey material.




Color

Color is typically where textures or patterns are connected to create color for opaque objects. This is where a wood color texture would go, for example.




Roughness

Diffuse roughness is how you would simulate a powdery surface like dried clay or dust.

 

 

Bump

Bump mapping is a great way to fake the appearance of physical detail using shading instead. If this is not set, it will use the global bump normal specified in the Properties section near the bottom of this page.

 

 

Double Sided

If on, illuminate both sides of the surface for this diffuse lobe, that is, this will illuminate the surface whose normal is pointing away from the camera (2-dimensional objects) as well. This is so the backface will be shaded instead of black. This is on by default.

 

Use Diffuse Color

This only applies when Double Sided is on. By default, this is on to use the Diffuse Color for the back color.

 

Back Color

This only applies when Double Sided is on. When Use Diffuse Color if off, this sets the back color (the color for the back side). By default, it uses the Diffuse Color but choosing a different color provides you with a way to make the backside of 2D objects appear differently.

 

Transmit Gain

This only applies when Double Sided is on. This sets the transmit gain as a multiplier. If it's 0.0 then the effect is off. Below the Transmit Color is bright blue.

 

 

Transmit Color

This only applies when Double Sided is on. This sets the transmit color which could be different than the diffuse or back color. This is ignored if Transmit Gain is zero. This effect is useful for thin objects like leaves or paper. Below there's a light placed in the interior of the object and some interior text can be seen as light transmits through the surface.

 

 

 

Expand
titleSpecular Parameters

Specular and Rough Specular Parameters

The specular parameters control specular reflection. This is where you might define how shiny or reflective an object is. Is it plastic, a polished marble table, or  is it a mirror? The Rough Specular lobe below this has identical settings and effects.

Note

There's also the option for Artistic and Physical controls. The Artistic controls allows you to manually alter the properties of the reflection to match your tastes. Using Physical (with provided presets) can provide you with a matching real-world response for those looking to duplicate reality without endless tweaking.

 

Specular Model

Select which specular model to use: Beckmann or Ggx. Ggx may be preferred for its "tail", or how the highlight has a soft fade from the center reflection of a lightsource. Left is Beckmann and Right is GGX with roughness 0.25.

 

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Specular Fresnel Mode

In Artistic mode, specular fresnel response will be controlled by its Face Color, Edge Color, and Fresnel Exponent.

In Physical mode, specular fresnel response will be controlled by its Refractive Index, Extinction Coefficient, and Edge Color.


Face Color (Artistic Mode)

Specular color at facing angle (0 degree incidence). Note that there is no separate gain control. To control the specular "gain", simply adjust the color value or connect it to a PxrExposure node. Below are different choices including textured at roughness 0.25.

 

 

Edge Color

Specular color at the glancing angle (90 degree incidence). To control the edge specular "gain", simply adjust the color value or connect it to a PxrExposure node. Below are different choices including textured at roughness 0.25. The Fresnel Exponent is also reduced here to make it more obvious.

 

Note

Understand that this control changes meaning in the Physical Mode and operates as a multiplier for the reflection result in Physical mode. You can control reflection intensity and even tint the result using this parameter in Physical Mode. Below we used black, 50% grey, and white.

 

 

 

Fresnel Exponent (Artistic Mode)

Specular fresnel curve exponent. Lower numbers reduces the effect of Face Color while increasing the effect of Edge Color. Higher numbers reverse this. If your face and edge colors are the same, then there is no visible effect. Below we use a red Face Color and green Edge Color and increase the Fresnel Exponent from 0.1 to 1.5 and finally 5.0 with a small roughness.

 

 

Refractive Index (Physical Mode)

This is a parameter meant to describe a physical refractive Index; the dielectric index of refraction for the material. Channel values for this parameter typically lie in the range 1 - 3. Since we support 3 color values to capture the spectral effect presets may be preferred over color pickers to avoid lots of tweaking.

 

Extinction Coefficient (Physical Mode)

Extinction Coefficient is a second refractive index for the material useful for characterizing metallic behaviors. Channel values for this parameter typically lie in the range 1 - 3. Since we support 3 color values to capture the spectral effect presets may be preferred over color pickers. When 0, the material reacts as a dielectric (glass, clearcoat). When non-zero, the material responds as a conductor would. Since this is based on physical values you should the presets more helpful than manual tweaking of settings. Below are presets for Copper, Gold, and Nickel.

 


Roughness

Specular roughness. A greater value produces rougher or "blurry" specular reflection. At 1.0 it resembles a diffuse surface and at 0.0 it's a perfectly clear reflection. Most objects will be realistic somewhere in between these values. Texturing this value may give you interesting effects like smudges, greasy fingerprints, and worn surfaces. Below are examples from 0.0 to 0.5 and finally 1.0 (diffuse).

 

 

Anisotropy

Controls the shape of the specular highlights and reflections. 0 means isotropic which produces the regular circular specular highlight. Values from -1.0 to 1.0 produce the range of ellipses (stretching) from wide to tall.

By default, the direction of anisotropy is controlled by the model texture parameters. If the Shading Tangent is specified, it is used instead. Below are examples of -1.0, 0.0, and 1.0.

 

 

Shading Tangent

Controls the anisotropy direction. Only valid when it is connected to a pattern. This is useful for making brushed metals. Below are three examples using textures and an Anisotropy of -10

 

 

Bump

Normal to use for the specular illumination. If this is not set, it will use the global bump normal specified in the Properties near the bottom of this page.

 

 

Double Sided

If on, illuminate on both sides of the surface for this specular lobe, that is, this will illuminate the surface whose normal is pointing away from the camera as well. This is on by default to avoid losing the specular result on the backside.

 

 

Rough Specular

Identical Specular parameters except it has a larger default roughness which is 0.6. This layer is intended for use with higher roughness settings than the Specular lobe above. Below from left to right: Rough Specular, Specular, both lobes combined.

 

 

 

 

Expand
titleClear Coat Parameters

Clear Coat

Clear coats are great for making a top glazed layer found in coated objects or paints like car paint, carbon fiber, and more. You can even use a bump exclusive to this layer to make for convincing coating imperfections. While roughness is available, this layer is intended for low amounts of roughness. You will notice in the parameter examples that the base diffuse is 50% grey to illustrate how this works as a coating. If you need a metallic surface, use the above Specular lobes.

Note

There's also the option for Artistic and Physical controls. The Artistic controls allows you to manually alter the properties of the reflection to match your tastes. Using Physical (with provided presets) can provide you with a matching real-world response for those looking to duplicate reality without endless tweaking.

 

 

Specular Model

Select which specular model to use: Beckmann or Ggx. Again, Ggx might be preferred for its "tail" or fade from the center highlight of reflected light sources.

 

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Specular Fresnel Mode

In Artistic mode, specular fresnel response will be controlled by its Face Color, Edge Color, and Fresnel Exponent.

In Physical mode, specular fresnel response will be controlled by its Refractive Index, Extinction Coefficient, and Edge Color.

 

Face Color (Artistic Mode)

Specular color at facing angle (0 degree incidence). Note that there is no separate gain control. To control the specular "gain", simply adjust the color value or connect it to a PxrExposure node.

 

 

Edge Color

Specular color at the glancing angle (90 degree incidence). To control the edge specular "gain", simply adjust the color value or connect it to a PxrExposure node.

Note

Understand that this control changes meaning in the Physical Mode and operates as a multiplier for the reflection result in Physical mode. You can control reflection intensity and even tint the result using this parameter in Physical Mode.

 

 

 

Fresnel Exponent (Artistic Mode)

Specular fresnel curve exponent. Lower numbers reduces the effect of Face Color while increasing the effect of Edge Color. Higher numbers reverse this. If your face and edge colors are the same, then there is no visible effect. Below we use a red Face Color and green Edge Color and increase the Fresnel Exponent from 0.1 to 1.5 and finally 5.0 with a small roughness.

 

Refractive Index (Physical Mode)

This is a parameter meant to describe a physical refractive Index; the dielectric index of refraction for the material. Channel values for this parameter typically lie in the range 1 - 3. Since we support 3 color values to capture the spectral effect presets may be preferred over color pickers to avoid lots of tweaking.

 

Extinction Coefficient (Physical Mode)

Extinction Coefficient is a second refractive index for the material useful for characterizing metallic behaviors. Channel values for this parameter typically lie in the range 1 - 3. Since we support 3 color values to capture the spectral effect presets may be preferred over color pickers. When 0, the material reacts as a dielectric (glass, clearcoat). When non-zero, the material responds as a conductor would. Since this is based on physical values you should the presets more helpful than manual tweaking of settings. Left to right are Copper, Gold, and Nickel.

 

 

Roughness

Specular roughness. A greater value produces rougher or "blurry" specular reflection. At 1.0 it resembles a diffuse surface and at 0.0 it's a perfectly clear reflection. Most objects will be realistic somewhere in between these values. Texturing this value may give you interesting effects like smudges, greasy fingerprints, and worn surfaces. Below are values 0.0, 0.5, and 1.0

 

 

Anisotropy

Controls the shape of the specular highlights and reflections. 0 means isotropy which produces the regular circular specular highlight. Values from -1.0 to 1.0 produce the range of ellipses (stretching) from wide to tall.

By default, the direction of anisotropy is controlled by the model texture parameters. If the Shading Tangent is specified, it is used instead. You may even "overdrive" the parameter by going further than -1.0 and 1.0.

 

 

Shading Tangent

Controls the anisotropy direction. Only valid when it is connected to a pattern. This is useful for making brushed metals.

 

 

Bump

Normal to use for the clear coat illumination. If this is not set, it will use the global bump normal specified in the Properties near the bottom of the page. Setting this separately can produce a "glazed" effect where you have a bumpy clearcoat above a smooth surface.

 

 

Double Sided

If on, illuminate on both sides of the surface for this clear coat lobe, that is, this will illuminate the surface whose normal is pointing away from the camera as well.

 

Specular Energy Compensation

Applies fresnel energy compensation to diffuse and subsurface illumination lobes. A value of 1.0 attempts to fully balance those results by darkening them against the specular and rough specular illumination responses.

Specular and Rough Specular roughness are also taken into account. The effect fades off as specular face or edge color approaches 1.0, so metals can add a diffuse baseline color. Look at Clearcoat Energy Compensation for a visual example.

 

Clearcoat Energy Compensation

Applies fresnel energy compensation to all lobes other than clearcoat itself. A value of 1.0 attempts to fully balance those results by darkening them against the clearcoat illumination response.

Clearcoat roughness is also taken into account. The effect fades off as clearcoat face or edge color approaches 1.0, so metals can add a diffuse baseline color. Left is 0.0 (default) Right is 1.0. Notice the darkening (changes in energy conservation) that happens.

 

 

 

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Expand
titleSubsurface Scattering Parameters

Subsurface Scattering Parameters

Subsurface Model

Select a subsurface scattering model: Jensen Dipole, d'Eon Better Dipole, Burley Normalized, and Multiple Mean Free Paths. The parameters are populated based on the model chosen and are valid for that model. If you change which model you use, your connections may be lost to invalid parameters.

Burley Normalized produces accurate effects while preserving details.

Jensen and d'Eon Dipoles are great for very translucent objects like gummies and extended art direction.

Multiple Mean Free Paths is great for texturing to produce color bleed easilyintuitively. While not necessarily physically correct, its intuitive scattering of textured colors works well for art direction while avoiding color shifting.

 

 

Gain

Subsurface scattering weight. Higher numbers increase the visibility of the subsurface scattering.

 

 

Color

Subsurface scattering color.

 

 

Mean Free Path Distance

Subsurface scattering mean free path distance (mfpd). This specifies how far the light travels inside an object and as a consequence how smooth the subsurface scattering is. This gets multiplied by the unit length set in the Properties section. Higher amounts make the object appear less opaque and more translucent as well as increase noise. Small amounts make the surface look diffuse and it may be more efficient to turn off the effect (0.0 Gain) if it's not visually important. Below we change the values from 8 to 16 and then 32. Notice how the sphere and pedestal become "softer" and more translucent. Your render times might also increase at high values due to noise generated by translucent objects.

 

 

Mean Free Path Color

How far the light travels in the Red, Green, and Blue spectra. This is scaled by Mean Free Path Distance. Different colors may spread more or less and provide interesting effects like the red color bleeding into shadow edges on skin. The RGB values correspond to how far the light travels in that color band. For example, and RGB value of 0.8 0.65 0.5 means Red spreads furthest at 0.8, then Green and finally Blue traveling the least distance in the object scatter result. Below we've taken out the center sphere and replaced it with a bright disk light at the back of the outer sphere. Note that the sphere and pedestal share the same material and lighting plays an important role in your result.

 

 

Post Tint

Tint that is applied at the end of the subsurface computation. Below on the left is a normal render and on the right a very light blue tint is added. If we want to apply the tint before the subsurface computation, set Irradiance Tint in the Properties section.

 

Multiple Mean Free Paths Description


Multiple Mean Free Paths operates differently than the others in a few significant ways. For most cases you will be happy with the results of the other models. However, there are instances where the user may want a non-physical way to control the colors of the scattering. The Mean Free Path Color in many models uses the supplied RGB value to determine the color scatter as noted in the parameter description. This means your result may have color shifts that are not desirable. Let's say you supply a textured color of RGB 0.51 0.28 0.31 which is a pink color. The scattering result will also include the green (0.28) and blue (0.31) responses. The Multiple Mean Free Paths model maintains the pink color. Below is an example using this scenario illustrating the differences. The texture is connected to the Color and Mean Free Path Color of the Jensen Dipole and to the Short and Long Colors of the Multiple Mean Free Paths model in addition. Note the color shift on the Jensen model (Left) while the Multiple Mean Free Paths version maintains the colors of the texture at all depths where connected.

 

 

Short Gain

Short subsurface gain or weight. This is only valid for Multiple Mean Free Paths subsurface model.

 


Short Color

Short subsurface color. This is only valid for Multiple Mean Free Paths subsurface model.


Long Gain

Long subsurface gain or weight. This is only valid for Multiple Mean Free Paths subsurface model. Operates the same as Short Gain.


Long Color

Long subsurface color. This is only valid for Multiple Mean Free Paths subsurface model.

 

Short MFP Distance

Short subsurface mean free path scalar distance. Below we go from 16 to 24 and finally 32.

 

 

Long MFP Distance

Short subsurface mean free path scalar distance. Below we go from 16 to 24 and finally 32.

 

 

Diffuse Computation Switch

Switch the subsurface computation to a diffuse computation if the dmfp is smaller than the ray footprint (not visible given the settings and distance). This is an optimization to ignore computing scattering, especially on far away objects or objects where the scattering scale is so low a diffuse computation is visually similar and much faster. This may be easier than manually setting the Gain to 0.0. Lower values increase the chance of rendering a diffuse computation instead of subsurface scattering.


Double Sided

If on, illuminate on both sides of the surface for this subsurface lobe, that is, this will illuminate the surface whose normal is pointing away from the camera as well.


Trace Control:

Consider Backside

Whether subsurface respects surfaces on the other side. This is for the hit side, not the illuminating side (which is subsurfaceDoubleSided):

  • "Off" - It will ignore surfaces on the other side completely. This is useful to make objects appear thicker than they are.
  • "On" - Normal mode, where the diffusion happens between the front and the first surface behind it.


Continuation Ray Mode

Control continuation ray mode:

"Off" - Simply trace out of the object (default).

"Last Hit" - Ignore internal geometry and jump to the last surface.

"All Hits" - Scatter (collect light) on all hits as the ray leaves the object. This can bring additional brightness, at the cost of additional noise.

Below left we use "All Hits" and you can plainly see the text "SUBSURFACE" embedded in the sphere. To the right it's set to "Off" which causes the embedded geometry to render incorrectly by clamping that falloff.

 

 

Max Continuation Hits

Maximum number of hits to test in all hits mode. This is only valid when Continuation Ray Mode equals All Hits

 

Follow Topology

Controls how strongly normals are considered in the subsurface computation. This may affect visible details created through bump mapping as well.

 

Trace Subset

Specify trace subset for inclusion/exclusion when struck by a ray indirectly.

 

 

Expand
titleSingle Scatter Parameters

Single Scattering Parameters

Single scatter is a simple and inexpensive effect for scattering effects. Below a disk light is placed inside the model and we render using no diffuse color and again with a default middle grey color.

 

 

Gain

Single scatter gain or weight.

 

 

Color

Single scatter color.

 

 

Mean Free Path

Single scattering mean free path scalar distance. This specifies how far the light travels inside an object and as a consequence how smooth the single scattering is. This gets multiplied by the unit length set in the Properties section. Larger values are more translucent.

 

 

Mean Free Path Color

How far the light travels in the R, G,  and B spectra. This is scaled by Mean Free Path Distance.

 

 

Directionality

Single scatter directionality:

1: forward scatter which is more light on the backside.

-1: backward scatter which is more light on the front side.

0:isotropic (no effect).

 

 

Refractive Index

Single scatter index of refraction.

 

 

Blur

Blur strength for single scatter.

 

 

Backside Direct Illum Gain

Gain for direct illumination from the other side.

 

 

Direction Tint

Tinting color for the Backside Direct Illum Gain.

 

 

Double Sided

If on, illuminate on both sides of the surface for this single scatter lobe, that is, this will illuminate the surface whose normal is pointing away from the camera as well.

 

 

Trace Control Parameters:

Consider Backside

Whether subsurface respects surfaces on the other side. This is for the hit side, not the illuminating side (which is singlescatterDoubleSided):

  • "Off" - It will ignore surfaces on the other side completely. This is useful to make objects apear thicker than they are.
  • "On" - Normal mode, where the diffusion happens between the front and the first surface behind it.

 

Continuation Ray Mode

Control continuation ray mode:

"Off" - Simply trace out of the object (default).

"Last Hit" - Ignore internal geometry and jump to the last surface.

"All Hits" - Scatter (collect light) on all hits as the ray leaves the object. This can bring additional brightness, at the cost of additional noise.

 

 

Max Continuation Hits

Maximum number of hits to test in all hits mode. This is only valid when Continuation Ray Mode equals All Hits

 

 

Direct Gain Mode

Control continuation ray mode:

"First Hit" - Simply trace to the next surface (this is tied to considerBackside).

"Last Hit" - Ignore internal geometry and jump to the last surface.

"All Hits" - Scatter (collect light) on all hits as the ray leaves the object. This can bring additional brightness, at the cost of additional noise.

 

 

Trace Subset

Specify trace subset for inclusion/exclusion when struck by a ray indirectly.

 

Scattering Globals

Irradiance Tint

A tint applied to illumination before being scattered by subsurface or single scatter.

 

Irradiance Roughness

Diffuse roughness to be applied for subsurface or single scatter. A value of 0 represents classic Lambertian shading model. Non-zero values increase the microfacet roughness for the Oren-Nayar shading model. A greater value produces rougher diffuse.

 

Unit Length

Subsurface and single scatter unit length. It is a multiplier on Mean Free Path Distance. Mean Free Path Distance is often measured in millimeters. If the scene is modeled in some other scale, Unit Length should be set accordingly. The default value of 0.1 is appropriate for scenes modeled in centimeters (the default in Maya) and Mean Free Path Distance measured in millimeters.

 

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