Design Nomenclature / Surface & Material
Roughness
Also called roughness map, microfacet roughness, alpha roughness
This entry has not been translated yet and is shown in English.
The statistical spread of microfacet normals across a surface, controlling how tightly reflected light clusters around the mirror direction. Low values concentrate energy into a small bright highlight; high values spread the same energy into a broad dim one. It is a distribution width, not a quantity of reflection.
In practice
Most authoring tools expose a perceptual roughness that gets squared before it reaches the shader, so the slider is not linear in the thing it names.
Not to be confused with
- GlossinessThe inverse parameterization of roughness: the same microfacet distribution addressed from the smooth end. High glossiness means a narrow lobe. Conversion is rarely a clean subtraction — pipelines apply their own remap curves or exponents, so a round trip through 1−x will shift the material.
- SpecularIn metal/rough conventions, a scalar remapping a dielectric's normal-incidence reflectance — default 0.5 meaning four percent, the top of the range around eight. In spec/gloss conventions, an RGB map giving that reflectance directly, which is also where conductors get their tint.
- Bump mapA grayscale texture read as height, from which the shader derives a normal perturbation by differencing neighboring texels. Encodes the same end result as a normal map at lower precision and without the ability to state direction independently of slope. Cheap, lossy, and still the right call for fine noise.