Can someone please explain the difference between metallic and smoothness? If something is smoother, I see that it reflects more … but isn’t that also what it means to be more metallic? It’s shinier?
Thanks for any insights.
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Metallic/Specular is visible from all sides but smoothness is only visible in Fresnel range
Metal objects reflect light differently than non metal objects. The “metallic” property is more literally “is this object made of metal or not” and should be either be 0.0 or 1.0 for real world objects. Using values in between can sometimes work as approximations of more complex real world materials, like a metal surface covered in dust, but generally should be avoided. The main difference between metal and non-metal (dielectric is the technical term) surfaces is metal reflects the same amount of light regardless of it’s facing toward you or away from you, and that light is tinted by the color of the metal. Dielectric materials reflect only some of the light when the surface is facing towards, but reflects more light the closer to a glancing angle it gets. This is the Fresnel @aliyeredon2 mentioned.
Smoothness on the other hand is how smooth or rough the surface is. A metal sphere can have a rough or smooth surface and look quite different.
Here’s a real world example of a rough steel sphere.
And a similar smooth steel sphere.
Compare this to something like a smooth onyx sphere.
Make note of how the reflection of the surface bellow the onyx sphere nearly disappear as the surface goes from facing away from the camera to towards the camera, where on the metal sphere the reflection of the ground stays almost uniform in brightness. Now, you might say “but wait, that’s not fair, the onyx sphere is black!”. Yes, the onyx sphere’s albedo, or diffuse color, is black. However technically speaking the metal sphere’s albedo is also black. The light that comes off of a metal surface is almost purely specular. The difference between the onyx sphere and the metal sphere is the onyx sphere is specularly reflecting only about 3% of the light when directly facing the view, where as the metal sphere is reflecting >80%.
Now there’s also specular color. That’s different than smoothness. The metallic value is a way to make it easier to make realistic materials by taking away control of the specular color from the user. A metallic value of 0.0 really just means a specular color of roughly sRGB (57, 57, 57). A metallic value of 1.0 means use the albedo texture’s color as the specular color, and use black for the albedo / diffuse.
Unity’s Material charts may help you here.
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