Research Blog – Materials
Hi in this blog I will be discussing materials and how they work within the Arnold render engine. This blog relates to the research I did for my rendering blog, so some of the information included will make more sense after reading that blog.
Materials or shaders are a set of surface parameters that determines how lighting will interact with geometry. Determining how much of a light ray is refracted or absorbed, this also determines light interactions such as refraction or pure reflection. Materials are often controlled by values and maps that contain alpha, colour or grey scale information.
In the case of Arnold it is a physically based render engine so its shaders and lights have simple roll outs that control values that equal real life lighting situations and surface behaviors.
The standard shader is a multi purpose shader that will be used in most cases for rendering surfaces in Arnold, as it can be use to make anything from plastic to metal to skin. As most parameters in PBR , the parameters for this shader are quite simple but not necessarily straightforward, it uses a specular workflow, not a metallic one.
Beside the major roll outs I will discuss, there is also access to bump mapping, subsurface scattering and emission.
The diffuse rollout controls the colour and roughness of the base colour of the material, this is a fairly simple part of the material. The major note comes with keeping the material physically accurate the weight of this parameter and and the weight of the specular parameter shouldn’t exceed a value of 1 when combined, as the the material wouldn’t produce more light rays than it absorved, an inaccurate calculation.
Specular Reflection and Reflection
The reflections for this material are controlled by two separate roll outs (specular and reflection) and they seemingly do the exact same thing. The biggest difference between the two is that specular has way more paramaeters and can reflect lights.
Specular indicates how reflective the surface is, its colour and strength can be controlled. It is here where the roughness of the highlights and reflections is controlled. This is why specular should also be used for blurry highlights. There is one last parameter which fresnel, this indicates how close to the edge the fresnel effect will take place and whether it takes place at all.
The reflection roll out has a limited amount of parameters and is advised to only be used for mirror like surfaces, it does not reflect light sources, so it is usually recommended to use this in combination with the specular parameters.
Refraction helps to create glass like materials, it is highly dependent on normal direction and will often require extra ray depth for it to work correctly on more complex materials. It is recommended to turn off the opaque option on any object with a refractive material as it will allow it to have internal retractions and have a more accurate shadow.
The most important parameter is the IOR (Index Of Refraction) this determines how much light traveling through is affected by the materials wavelength, the higher it is the more distorted light will be shown passing through it. There is also an option to make this value affect the Fresnel at normal. Beside this you can control the colour and weight of the refraction. There are is another way of creating colour for the material, and that is transmittance, this is a colour that determines how much the material is affected by it depending on how think the object it is.
Solid Angle. (2009). Diffuse. Retrieved August 10, 2016, from Solid Angle Support, https://support.solidangle.com/display/AFMUG/Diffuse
Solid Angle. (2009). Reflection. Retrieved August 10, 2016, from Solid Angle Support, https://support.solidangle.com/display/AFMUG/Reflection
Solid Angle. (2009). SSS layers. Retrieved August 10, 2016, from Solid Angle Support, https://support.solidangle.com/display/AFMUG/SSS+Layers
Solid Angle. (2009). Standard. Retrieved August 10, 2016, from Solid Angle Support, https://support.solidangle.com/display/AFMUG/Standard
Solid Angle. Specular. Retrieved August 10, 2016, from Solid Angle Support, https://support.solidangle.com/display/AFMUG/Specular