Arnold for Maya – Transmission Scattering (Ray Traced SSS)

Software:
Maya 2018 | Arnold 5

Scatter

The Arnold Standard Surface Shader’s Transmission Scattering options can be used for simulating highly realistic volumetrically ray-traced sub-surface-scattering suitable for materials like wax, soap, milk etc.

While the Transmission Depth attribute controls volumetric light absorption within the object (fog), the Scatter attribute controls what percentage of the light will be scattered instead of absorbed, effectively creating the murky effect of semi-transparent materials.

Note that for the scattering effect to work Scatter must have a dominant percentage value, and the Depth attribute must generally be much lower (shallower) than what would create coloring without scattering, otherwise the object will continue to look transparent and lacking the internal substance that we want to simulate.

Also note that the Opaque attribute must be unchecked in the Arnold attributes of the object’s shape node for the light to be able to pass into the mesh and illuminate the volume.
*This is actually a “cheat”, because physical semi-transparency has to be simulated by indirect light calculation or caustics, but for dense volumes like wax it’s very effective and the loss of realism is insignificant.

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You can simulate the effect more accurately by rendering caustics,
In that case the Opaque attribute in the Arnold attributes of the object’s shape node must be checked and more steps must be taken allow refractive caustics to be ray-traced.

Note that simulating the effect using caustics will be very demanding in Transmission samples and Ray Depth.

Scatter_Caustics

Related:
Translucency

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Using Arnold’s Ambient Occlusion node to create an eroding paint shader effect

Software:
Maya 2018 | Arnold 5

Arnold’s Ambient Occlusion (dirt) node can be used as a procedural mask to create interesting material effects like in this example of paint that is eroded at the model’s bulging areas to reveal metal beneath it.

In this shader’s case the Ambient Occlusion node is connected to the Mix property of an Arnold Mix shader, that blends between two different Arnold Standard Surface shaders, one simulating the underlying tin metal, and the other simulating the red paint that covers it.

Note that in the Ambient Occlusion node the Invert Normals property is checked, so that the effect will create a mask for the bulges and not for the creases,
And also that the Self Only property is checked so that the node will behave as a fixed object mask disregarding the proximity of other objects.
In this example the output of the Ambient Occlusion node is also process using a Remap Value node to increase it’s contrast so it will define borders between the areas.

Paint-Metal.jpeg

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Arnold for Maya refractive caustics

Software:
Maya 2018 | Arnold 5

An account of the drastic measures that need to be taken in order to ‘persuade’ Arnold for Maya to render refractive caustics.

  1. In the refractive object’s shape attributes,
    Under ‘Arnold’, ‘Opaque’ must remain checked.
    * This is unintuitive but when refractive caustics are calculated there is no need for transparent shadows. the caustics pattern is in fact the light refracting through the object.
  2. The refractive object’s aiStandardSurface shader must have it’s Transmission layer active.
    For a colored refractive object, Transmission Weight should be 1.0,
    A color should be selected, and the density of the color should be controlled with the Depth attribute (higher values make the color less dens).
    In the shader’s advance attributes, check ‘Caustics’.
    In the shader’s Specular layer, set the IOR to match your material.
    * The default of 1.52 is the IOR for glass, and water would be IOR 1.33 for example.
  3. For refractive caustics to be rendered, the light source must be an Arnold Mesh Light,
    And in its shape attributes, under Light Attributes ‘Light Visible’ must be checked.
  4. In many cases, in order for the caustics pattern’s intensity to be correct,
    The ‘Indirect Clamp Value’ must be raised in Render Settings > Arnold Renderer, under Clamping.
  5. In some cases the Transmission value under Ray Depth in Render Settings > Arnold Renderer must be increased for the caustics to render properly.
    * Light simulation must be able refract through all the relevant surfaces.
  6. To increase the caustics render quality, the number of Diffuse samples must be raised in Render Settings > Arnold Renderer.
    * This may be unintuitive, but the caustics pattern is actually part of the Diffuse rendering of the surface upon which the caustics are appearing.

That’s it!
Hope you find this useful 🙂

Arnold_Coustics_AArnold_Coustics_BArnold_Coustics_C

 

 

Simple Toon shader setup in Maya & Arnold

Software:
Maya 2018

Use a Surface Luminance node as a V coordinate input value for a Ramp (V Ramp) node containing the toon colors.

* Note that the Clamp node is important so results will be ass expected, it clamps the Surface Luminance values to 0.99 so the V coordinate will nor cycle back to the beginning of the Ramp.

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Related:
Toon Shading in V-Ray for Maya

Arnold for Maya Standard Surface Shader Translucency / Paper Shader

Software:
Maya 2018 | Arnold 5

Translucent
In this example, the lamp shade has a Translucent material

The Subsurface component of the Arnold Standard Surface shader (aiStandardSurface) controls Sub Surface Scattering (SSS).
When the ‘Thin Walled’ option is checked in the Geometry attributes of the shader, the Subsurface isn’t rendered as a full volume of material like soap or skin/flesh (the effect that is traditionally called Subsurface Scattering – SSS) but as a thin paper-like translucent surface like paper, thin cloth thin leaves, lamp shades etc. (the effect traditionally called Translucency or ‘Paper Shader’)

* Note that this option is suitable mainly for polygon surfaces without thickness (just one side)

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To create a Translucent shader with Arnold:

Subsurface Weight must be higher than 0.0 for the effect to be computed.

In Geometry, check Thin Walled for the SSS to be rendered as Translucency (Paper Shader).

Extra options:

Use samplerInfo Node Facing Ratio output in Subsurface weight to add realism by changing the weight by angle.

Multiply weave texture with Facing Ratio to simulate fabric translucency.

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