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LuxRender Materials GlossyTranslucent

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Glossy translucent.jpg

Glossy Translucent represents a diffuse surface with both a transmission component AND a varnish coat. It is effectively a combination of glossy and matte translucent. Remember that as a result of this, it is the slowest to render of the four "basic" materials, you should use it only when you need both transmission and glossyiness. This material is well suited to most organic materials, including skin, internal organs, leaves, eyes, milk, ketchup, alien slime, etc. It can also work well for soap, and certain plastics.

Contents

Options

Note: Glossy translucent does not have matte translucent's "energy conserving" option, it acts as though it was always on. So transmission will always be calculated based on the leftover light from the reflection steps.

Diffuse color

This is the color of the matte base layer, and will be the main color of the material, assuming it is set above .4-.5 or so. Any light not reflected is transmitted, so lower than that it will be mainly the transmission/volume color

Transmission color

This determines the color of light that transmits through the material. For best results, you should leave this as 1.0 (full white) and use the object's volume to give the material its internal color. This allows for volumetric color absorption and, optionally, subsurface scattering. Color from the transmission setting is applied uniformly to transmitted light, and can make your object look unnaturally uniform in color, so using a volume is recommended.

Specular color and IOR

This is the color of the varnish coat. In many real world materials, all color is in the base rather than the gloss, so this color should often be left as gray. (For example, the paint on porcelain is applied before the glaze, so your paint texture should only be on the diffuse channel). Darker colors will make the material less shiny, especially at shallow angles. Optionally, you can specify an index of refraction for the coating material, however this will prevent you from coloring the coating, it will always be gray. This can be useful if you want to specify a specific material making up the coating. For example, a wet floor would have IOR = 1.333, the IOR of water.

The specular color should not be set higher than about .25, and many everyday materials will have much lower values, such as .03-.05. The IOR and specular color are related via the formula IOR = (sqrt(Ks)+1)/(1-sqrt(Ks)) (Ks is the proper term for specular color). This translates a specular color of .25 to an index of refraction of ~3. A specular color of .05 results in an IOR of approximately 1.6, which is still a bit on the high side. A specular color of 1.0 (full white) results in an IOR of infinity, which is impossible. Even the most extreme metamaterials would only have a specular color of approximately 0.9 (IOR = 40)

Roughness

This determines how shiny the material is by varying the roughness of microfacets. If your exporter uses the exponent to control roughness, higher values are shinier, with 0 being matte. If your exporter uses the direct roughness control, lower values are shinier, with 0 being a perfect reflector and .8 being matte. Values between .8 and 1 are an unrealistic "super-matte" and should be avoided.

Absorption color/depth

These allow you to specify the color and depth of light absorbtion by the surface coating. Note that since this is an absorption color, it will seem to work "backwards". Setting it to blue will cause blue light to be absorbed, leaving you with a yellow-orange appearance. To defeat this option, set the color to full black (0.0). This parameter is not related to volume absorption.

Examples of various absorption settings

Multibounce

The option will simulate light being scattered at the surface by things such as fuzz or fine hair. It is useful when using glossy translucent for a skin or cloth material, and will give a soft, fuzzy appearance:

A multibounce luxball, using the basic glossy material

Two-sided

This option will enable a second set of specular color, absorption, and roughness controls for the backface of the material, that is, the side opposite the normal. This is useful for planar surfaces and open meshes, such as leaves or textiles. Many of these items are much less glossy on the back, this option allows for that. If this option is left off, the backface will use the same settings as the frontface.


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