If you're familiar with PBR materials, for example because you've used them in other programs such as Blender, Unity, Substance, and others, then you know there are two workflows, called Metallic Roughness and Specular Glossiness...
Video Transcript
Hello everyone! If you're familiar with PBR materials, for example because you've used them in other programs such as Blender, Unity, Substance, and others, then you know there are two workflows, called Metallic Roughness and Specular Glossiness. Depending on the workflow used, you need to specify certain information.
In Unreal, the workflow used is Metallic, so in a Material we need to specify at least Base Color, Metallic, and Roughness information, plus optionally a Normal Map to simulate details through a specific Texture. If we want to create a basic Material, however, we only need to set the first three channels I just mentioned.
We always start with the Metallic channel, where obviously 0 indicates a non-metal and 1 indicates a pure metal. Base Color defines the base diffuse color of a non-metallic object, while for metals it determines the tint of the specular reflections. The Roughness parameter specifies how rough or irregular a surface is: with 0 we'll have a perfectly smooth or polished surface, while with 1 we'll have a very rough surface that appears matte. For example, to create a perfect mirror, we would use pure white color, Metallic set to 1, and Roughness set to 0.
In Unreal Materials, however, there is also the Specular channel, which can cause some confusion, especially considering that Specular Glossiness is the name of the other PBR workflow. Moreover, if you use a purely metallic Material, changing the Specular value seems to have no effect. So what is the Specular parameter used for in this context? In Unreal Engine, this value is used to control the base reflectivity of non-metallic materials only. That's why this parameter is completely ignored if Metallic is set to 1.
So, for a metallic material, the correct configuration obviously comes from setting Metallic to 1, the color of its specular reflections defined by Base Color, and a Roughness value chosen according to the shininess of its surface: low for a shiny metal and high for a matte or brushed one. In these conditions, the Specular parameter has no effect.
As for non-metallic materials, in that case Specular allows you to control the base intensity of their reflectivity. The default value in new Unreal Materials is 0.5, which represents 4% specular reflectivity. This last statement, taken directly from Unreal's online documentation, creates even more confusion. How is it possible that a value of 0.5, in a range from 0 to 1 for the Specular field, corresponds to 4%, which should be 0.04?
The fact is that the actual reflectivity value used by Unreal is the Specular value we set in the Material multiplied by 0.08. The value 0.08 represents the maximum reflectivity for dielectric materials in Unreal at an incidence angle of 0, that is, when the surface is viewed straight on. As the angle increases, reflectivity also increases, in accordance with Fresnel's law, and Unreal automatically takes care of this aspect. So, when you see this field, you're actually setting a reflectivity value between 0% and 8% for the surface when it's viewed frontally.
In any case, the default value of 0.5, which corresponds to 4% reflectivity, is fine for most non-metallic materials such as plastic, glass, rubber, wood, ceramic, human skin, and others. If we set Specular to 1, we get a maximum reflectivity of 8%, generally reached by diamonds, certain gemstones, and just a few other materials. The Specular value should never be set below 0.25, which corresponds to a reflectivity of 2% when the incidence angle is 0.
In conclusion, you can think of Specular as how strong the light reflection is, and Roughness as how sharp or diffuse that reflection appears. Unless you know the exact reflectivity value of the non-metallic material you want to create, leave Specular at its default value of 0.5. If you do know that value, divide it by 0.08 to get the correct Specular parameter value. For example, water has a reflectivity of 2%, so we take 0.02 divided by 0.08, which gives us 0.25.
Alright, that's it for this short video! If you found it useful, you can thank me with a Like and by subscribing to the channel! Don't forget to turn on notifications so you won't miss the next tutorials. See you soon!