Diffuse reflection is the scattering of incoming light in many directions when it hits a rough or matte surface, so the surface looks similar from most viewing angles. It is the opposite of mirror-like specular reflection. Paper, clay, and unpolished stone are largely diffuse reflectors.
A rough or matte surface has microscopic irregularities that scatter incoming light in many directions at once. The result is that roughly the same amount of light reaches a viewer no matter where they stand, so the surface keeps a consistent color and brightness across viewing angles. This is the behavior captured by the Lambertian model.
In physically based rendering, the diffuse component represents this scattered light and is usually paired with a specular component that handles mirror-like reflection. Most everyday matte materials, from cardboard to painted drywall, are dominated by diffuse reflection.
Diffuse-dominant materials are the reliable case for 3D capture. Because a diffuse point looks the same from every angle, photographs taken from different cameras agree on its color, and reconstruction can triangulate it to a single, stable 3D location. This is why matte objects reconstruct cleanly while glossy or transparent ones do not.
When a 3D capture looks crisp, it is usually because the subject was mostly diffuse. Understanding this helps teams predict which products will be straightforward to bring into 3D and which will need more careful capture.
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