In PBR, what does Roughness control, and how does it affect reflections?

• A. Roughness controls how glossy a surface appears; higher roughness reduces sharp reflections, lower roughness increases sharp reflections.
• B. Roughness controls color.
• C. Roughness controls emission.
• D. Roughness controls normals.

Answer: (A)

Roughness describes how rough or smooth a surface’s micro-geometry is, and it controls how reflections form on that surface. When roughness is low, the surface acts like a smooth mirror, so reflections are sharp and clear because most tiny facets align to reflect light in the same direction. When roughness is high, the tiny facets face many different directions, causing reflections to blur and spread into a softer, more diffuse highlight. That’s why polished metal looks highly reflective and crisp, while rough plaster or chalky paint looks dull with fuzzy reflections. In practice, roughness is often stored as a grayscale map: darker values mean smoother, crisper reflections; lighter values mean rougher, blurrier reflections. It doesn’t directly change color, emission, or normals.