Bump Maps

A bump map isn't really a texture but is used in conjunction with one to simulate 3D surfaces on a 3D object. This generally reduces the polygon count of an object; instead of meshing out, say, a bumpy dinosaur skin by creating a 20,000-polygon model, you can use a bump map and a 2,000 polygon-count model to simulate this detail. The bump map is a grayscale map that the game or modeling engine uses to provide artificial relief on the existing texture (see Figure 1.7). The engine interprets the varying shades of gray, with white being the highest and black being the lowest.

There's also a disadvantage to using bump maps. For the relief, or visual depth, on the rendered model, the light source always seems to come from one direction—usually above. An advanced technique to providing a much better relief that changes with lighting direction (and makes the model appear extremely detailed) is using normal maps.

Note

Although people often use the words bump map and displacement map interchangeably, a displacement map is more appropriately a term for a texture map that creates the relief for a terrain. A game engine can use a displacement map, which is similar to a grayscale bump map, to create a height map for the terrain in a game. The engine translates the shades of gray on the map to build a surface accordingly. The more white on the map, the higher the terrain's surface; the more black on the map, the flatter the surface.

2D texture Bump map

Rendered 3D model

Figure 1.7 A bump map gives the model the illusion of a 3D texture during render time.

2D texture Bump map

Rendered 3D model

Figure 1.7 A bump map gives the model the illusion of a 3D texture during render time.

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