Bump map

A bump map describes fine surface irregularities in shades of grey. Light values read as high, dark values as low. The render engine looks at how these values change between neighbouring pixels, works out the slope, and shades the surface accordingly. Plaster texture, the grain of stone or faint wood grain then appear on a flat face.

When to use it

Bump maps are simple and light, and they can often be made quickly from a greyscale copy of a texture. That makes them a practical choice for fine, irregular detail, especially on surfaces away from the camera: facade render, concrete, asphalt, leather.

Its limits

• It only fools the lighting; the silhouette and cast shadows stay the same.
• It loses conviction on deep grooves and ridges, where displacement is the right tool.
• Too much strength makes a surface look dirty or noisy.
• A normal map, which stores direction directly, usually gives crisper detail.

In practice bump, normal and displacement are partners, not rivals. A good material often uses displacement for large forms, a normal map for mid-scale detail and bump for the finest surface texture, so it holds up even as the camera moves closer.