EMPEROR'S NEW CLOTHES

Let's look at the new BRDF models in Octane. Until the V3.08 version, Octane was using its original BRDF. There was conservation of energy in this model, but it was not fully functioning. In other words, the amount of reflected light was the same as the incoming light (in other words, always 100%). Along with the new BRDF models, Octane's material arsenal is much more advanced. The materials you will create from now on will be more plausible and accurate materials that conform to physical laws.

皇帝的新衣服

让我们看看Octane中的新BRDF模型。 在V3.08版本之前，Octane一直使用其原始的BRDF。 在此模型中，存在能量守恒，但是它没有完全发挥作用。 换句话说，反射光的量与入射光相同（换句话说，总是100％）。 与新的BRDF模型一起，Octane的材质库更加先进。 从现在开始您将创建的材质将是符合物理定律的更合理，更准确的材质。

You can see the difference between the original Octane BRDF and the new BRDF models as shown in the figure below.

您可以看到原始的Octane BRDF与新的BRDF模型之间的差异，如下图所示。

ENERGY CONSERVATION IN OCTANE

The biggest difference between the new BRDF models is the compliance with the law of conservation of energy. In the original Octane BRDF this was always 100%. So energy conservation was not fully achieved. We can test it with new BRDF models. For example, create a sphere and put it anywhere in your scene. Then create a Texture Environment from the Live Viewer. Go to RGB Spectrum in Texture Environment settings and make the color white (230, 230, 230). Then create an Octane Glossy Material. Change the following in the material settings.

Diffuse: Full Black (0, 0, 0)

Specular: White Color (230, 230, 230)

Roughness: 0.5

Index: 1 (To disable Fresnel)

Finally, go to the Settings/Kernel and select Pathtracing.

Now run LV. You will not see anything other than a white screen. But the sphere is there. Why?. Even if the material and the environment are the same color, the total energy of the light reflected from sphere must not be more than the total energy of the incoming light, according to the law of conservation of energy. We see a white image because the original Octane BRDF is equalizes the reflected light energy and the incoming light energy (it's always %100).

Now change the BRDF models this time, for example choose "Beckmann". You will see that Sphere is a little more visible. What happens here is that the reflected light's energy is less than the incoming light's energy. So the new BRDF models fit exactly into the Law of Conservation of Energy. You can see the differences in the picture below.

Octane能量守恒

新的BRDF模型之间的最大区别是遵守能量守恒定律。在原始的Octane BRDF中，该比例始终为100％。因此没有充分实现节能。我们可以使用新的BRDF模型对其进行测试。例如，创建一个球体并将其放置在场景中的任何位置。然后从实时查看器创建一个纹理环境。在“纹理环境”设置中转到“ RGB光谱”，然后将颜色设置为白色（230、230、230）。然后创建一个Octane光泽材质。在材质设置中更改以下内容。

漫射：全黑（0，0，0）

高光：白色（230，230，230）

粗糙度：0.5

索引：1（禁用菲涅耳）

最后，转到“设置/内核”，然后选择“路径跟踪”。

现在运行LV。除白屏外，您将看不到其他任何东西。但是球体在那里。为什么？。根据能量守恒定律，即使材质和环境的颜色相同，从球体反射的光的总能量也不得大于入射光的总能量。我们看到一个白色图像，因为原始的Octane BRDF使反射光能和入射光能相等（始终为100％）。

现在，这次更改BRDF模型，例如选择“贝克曼”。您将看到Sphere更加可见。此处发生的是反射光的能量小于入射光的能量。因此，新的BRDF模型完全符合能源守恒定律。您可以在下图中看到差异。

MICROFACETS IN OCTANE (Roughness)

In the previous chapter, we briefly mentioned microfacets. With the new BRDF models, Octane tries to mimic the roughness while redefining the surface at the micro geometry level according to the "Microfacet" functions. These functions are the commonly used "Beckmann", "GGX" and "Ward" BRDF functions. Unlike the original Octane BRDF, these 3 models allow you to create features such as "Fresnel Effect" and "Anisotropic Roughness" not previously available in Octane. These features make very nice and realistic results in Octane material creation.

The biggest difference between these 3 microfacet models is the Specular Lobe. These specular lobes are defined by the microfacet NDF (Normal Distribution Function). NDF describes the distribution of microfacets for the surface and unique to each BRDF model. Also this function is most responsible for the size and shape of the specular highlight. In the pictures below, you see the Specular Lobes of all 3 models with a roughness value of 0.2. GGX produces more specular tail than other models. This is because the angle of the Microfacet normal differs from the Surface Normal, so the GGX does not fall below a certain value.

Microfacet is a very complex theory. You can get more detailed information from the below link:

https://www.cs.cornell.edu/~srm/publications/EGSR07-btdf.pdf.

Octane中的微细面（粗糙度）

在上一章中，我们简要提到了微面。使用新的BRDF模型，Octane尝试模仿粗糙度，同时根据“ Microfacet”功能在微观几何级别重新定义表面。这些功能是常用的“贝克曼”，“ GGX”和“沃德” BRDF功能。与原始的Octane BRDF不同，这3个模型允许您创建功能，例如Octane以前不可用的“菲涅耳效应”和“各向异性粗糙度”。这些功能在创建Octane材质时取得了非常不错的逼真效果。

这3个微面模型之间的最大区别是“镜面波瓣”。这些镜面波瓣由微面NDF（正态分布函数）定义。 NDF描述了表面的微面分布，并且对于每个BRDF模型都是唯一的。同样，此功能对镜面高光的大小和形状最负责。在下面的图片中，您可以看到所有3个模型的“镜面波瓣”，其粗糙度值为0.2。 GGX比其他模型产生更多的镜面反射尾巴。这是因为Microfacet法线的角度与表面法线不同，因此GGX不会低于某个值。

Microfacet是一个非常复杂的理论。您可以从以下链接获取更多详细信息：

https://www.cs.cornell.edu/~srm/publications/EGSR07-btdf.pdf。

ANISOTROPY IN OCTANE

One of the new material properties of octane is "Anisotropy". You can get complex metallic surfaces thanks to this feature, which is a plus for new BRDF models. As we have already mentioned, 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 can increase or decrease the roughness according to the BRDF model you choose. The results will be different for every 3 BRDF because of their Microfacet functions.

Octane的各向异性

Octane的新材质特性之一是“各向异性”。 借助此功能，您可以获得复杂的金属表面，这对于新的BRDF型号来说是一个加号。 正如我们已经提到的，各向异性是通过围绕曲面的法线旋转反射值而引起的。 各向异性表面的例子包括抛光金属，人发，毛皮和木材。 在Octane中，可以将各向异性功能用于3个新的BRDF模型。 您可以根据选择的BRDF模型增加或减少粗糙度。 由于其Microfacet功能，每3个BRDF的结果将有所不同。