GLOSSY MATERIAL

As we mentioned in the BRDF section, there were no requirements to produce a physical accuracy reflection in the original BRDF of Octane. So when using Glossy material you can now use physical BRDFs Beckmann, GGX and Ward. With these models you can now create real surface properties such as the physical precision of the specular lobes, the fresnel effect, the law of conservation of energy, and anisotropy. As we will see in the future, you can create extremely realistic reflective surfaces with the "Metal Material" feature, which allows you to use complex refraction values that only show metallic features.

Glossy material is used to create materials with reflective properties. In reflection law, when the photon is hit by a surface, the reflection angle of light is equal to the angle of incidence. Photons do not spread around the surface as it is in the diffuse reflection. These surfaces are metal, plastic, and so on.

The energy of the irradiance from any point (I) to the point (x) on a smooth surface is reflected from this point in a special direction called the specular direction (see below diagram).


The radiance energy that comes to the surface usually reflects the light by creating a light lobe around the specular direction (Also called "specular lobe"). The shape of this lobe is determined by the difference between the exit angle of the light and the specular direction. These Specular Lobes can grow and shrink depending on the roughness value on the surface.


Reflection (actually Specular Reflection) is an important topic in CGI. Years ago we were dealing with reflection forms that were not physically correct (eg Phong BRDF). At that time, there were BRDFs, such as the Cook-Torrence or the Beckmann-Spizzichino, which had already been described but they wanted a computational power that exceeded that of their computers at that time. Now our computers are speeding up to calculate these models. But in response to this speed, we have to prepare materials by a good observation and knowledge without haste. Because entering an immediate value and expecting a realistic output often results in frustration. We repeat: Read and practice. There is no other way.


Now let's look at Octane's Glossy material options. We will not explain the parameters that we have already explained in Diffuse section and which most of the common material uses. When you select Glossy, some new parameters will appear. We will only explain these new parameters. Diffuse and Roughness parameters are important in creating Glossy Material, so we will include both of these explanations.



DIFFUSE

The Diffuse parameter gives the material its color. In computer graphics terminology this is also referred to as “Base Color” or “Albedo”. Diffuse color can be set using a value or by using a procedural or image based texture. But you should be careful to use diffuse in conjunction with specular color on metal-like surfaces. We will explain this in more detail in the Specular option.


SPECULAR

From this parameter you can adjust the amount of reflection on the surface. We have already explained the options here in Diffuse material section. Float value is disabled when using RGB color. And vice versa. For example, if you are creating a metal surface, it is recommended that you make RGB values ​​almost the same as diffuse color, because in the real world, the specular highlight colors of metallic surfaces are colorful. This is due to the characteristic of metals called "Conductor". Metals transmit heat and electricity well. Because of this, it is called "Conductor". They absorb different wavelenghts of the light and the color of the reflected light is the Specular Highlight. Therefore, the color of the metal material is also due to this reflected light. Gold metal, for example, appears specularly yellow as it absorbs the blue wave of visible light.

On surfaces called dielectric, there is an opposite situation, they can not transmit heat and electricity well, and when light hits these surfaces, most of the light wavelenght is not absorbed. For example, surfaces such as plastic are in the Dielectric category. If you are creating a plastic material, you can use the float parameter instead of RGB for the specular color. Thus your specular highlight will be determined according to the color of the light (mostly white).

All of this is a small recommendation if you want to make realistic material. For things like the Mograph, you can enter pretty eye-catching values. You can even use diffuse color for metallic surfaces. However, it is important to know that you should use diffuse color very lightly on reflective surfaces such as metals for a realistic result.

In the picture below, there are renders in various Specular values with a Roughness value of 0.



ROUGHNESS

Perhaps the most important parameter of glossy material is roughness. It is a parameter that must be used absolutely for materials with reflective characteristics. This is the practical counterpart of the "microfacet" theory that we briefly describe in the BRDF section. Roughness controls the amount of specular reflection scattered on the surface. In the real world, all surfaces are rough. Even the mirror that appears as the smoothest surface is rough when viewed very closely. Here the Microfacet theory is developed on this real phenomenon. If you are wondering how the surfaces look so closely, you can look at images taken by electron microscopy (search google). You will be surprised.


Specular surfaces usually reflect light by creating a light lobe around the specular reflection direction. The shape of this lobe is determined by the difference between the exit angle of the light and the specular direction. This resulting lobe creates blurring effect due to its roughness. The larger the specular lobes, the more blur and the surface looks darker. In computer terminology, this is called "reflection blur". This value behaves in accordance with the law of conservation of energy in BRDFs that provide physical results. In other words, the incoming light is scattered in more directions during reflection, resulting in energy loss. This is the explanation that Lob goes towards darkness as the size increases. Even at extreme values, the surface almost starts to show diffuse properties (see the picture below. The other 3 brdf except the octane show this feature).  


With this parameter you can also use the options we mentioned in the Diffuse section. Do not forget that not RGB but Greyscale values are important. So you must enter Greyscale values when using RGB. Or you can use Float value. You can also get very creative results with texture use.

In Octane's new BRDF models, the roughness parameter now produces more realistic results. You can see the roughness values according to different BRDF models in the picture below.



ANISOTROPY

This parameter is present in our material arsenal as a result of the new BRDF models. The anisotropy is the reflection value changes by turning the surface around its normal. Examples of anisotropic surfaces include polished metal, human hair, fur and wood. In Octane, you can use the anisotropy feature for 3 new BRDF models. You should enter the roughness value for to use this effect. You can increase or decrease the roughness according to the BRDF model you choose. Anisotropy has several options, let's explain them.

Anisotropy: From here you can determine the amount of anisotropy you will apply to the surface. It can be a negative or positive value. Do not forget to enter a value for the roughness.

Rotation: From here you can rotate anisotropy by defining a texture. With the texture you use, you can get a wide variety of effects by turning the surface normals. You can use any texture image or procedural, provided that it's a gray scale. Even with the new OSL texture, you can create completely different results.

If you want to make a realistic anisotropy, be sure to first observe the physical properties of the material you will create. All anisotropy surfaces shows absolutely roughness / specular and IOR properties. Without this, you can not create an anisotropic surface. In particular, surfaces showing anisotropic properties such as polished metal, wood and fur show distinct microfacet features from each other. Also take a shot of the subject for reference if you have to. Finally, set your model's surface normals and UV map settings according to your objective.

The following picture shows the anisotropy properties of different BRDF models. In this image the roughness value is fixed and a gray scale image texture is used for rotation.



Sheen

This is mainly used for simulating clothes and velvet/satin like materials. It's basically increasing reflectance for grazing angle with varying roughness. Less roughness means a sharper peak of sheen reflection around the grazing angle, higher roughness means a less sharp peak and a more spread out sheen reflection across the fabric surface.

This feature works in new BRDF models. So choose the other BRDFs instead of the default Octane BRDF. Sheen is also a BRDF model and is written according to the formulas on this link.

To use Sheen, create a "Glossy" material and enter the values you see in the picture below to get started. The parameter that is important after completing the main material setup is the "Roughness" parameter. You can change the sheen look by playing with this parameter. It is also possible to use Sheen more efficiently with Mix material.

The Sheen feature is definitely a great addition to Octane material creation. Previously we used "Falloff" texture to make fake fabric. We no longer need this type of tricks thanks to the sheen feature.



FILM WIDTH & FILM INDEX

Film width simulates the look of a thin film of material on the surface. This is useful when you want to create an effect such as the rainbow colors that appear on the surface of an oil slick. Or a soap bubble. Larger values increase the strength of the effect. The Film Index controls the Index of Refraction of the thin film, use this option to adjust the colors visible in the film. For this parameter you can also enter RGB color/Float Value and image/procedural texture values. In the picture below, a gray scale image texture is used for Film width. Film Index is 2.2.



INDEX (INDEX OF REFRACTION)

This parameter determines the reflection strength of the surface according to the fresnel reflection law. Also called IOR or Refractive Index. Fresnel is the surface reflection of the observed angle and the surface IOR (Index of Refraction) values. The Fresnel effect is, which reflects less light from the direct-facing surfaces than the other angles. In this case the value you enter will change the Fresnel reflection (see below picture).

in reality each surface has a refractive index. For example, if you want to enter a correct value in the index part here, be sure to use https://refractiveindex.info/ as your online resource. The "Selected data for 3D artist" section on the main drop down menu is a good start. The values that concern us here are the "n" and "k" values. These values are actually called "complex index of refraction". But there is no area in Octane where you can enter these values except "Metal Material". In this case, you can only enter "n" in the index section. The number "k" is the value of extinction coefficient. Since the index is a complex phenomenon, we will refer again to both "Specular" and "Metal Material" sections.