A displacement map is a bitmap (or procedural texture) that is applied to surface geometry (generally a polygon mesh or particle group). The grayscale values of that image are then used to physically displace the geometry. White represents the maximum displacement along the given axis, while black represents no displacement. The maximum value is determined by the user, measured in whatever units the program is set to. See Column A and B for examples of displacement mapping.
A bump map is a bitmap (or procedural texture) that is applied to a surface, and only a surface. Bump mapping is a surface shader, meaning that it does not actually alter the physical geometry of an object. The shader simulates small protrusions or 'bumps' on the surface. White values represent the peaks of the bumps, while black values represent no bump. Since these are not physically there, the only way they show up is by interacting with light. The surface is shaded according to the direction that the light comes from. The effect can be very convincing from a distance, however they fail miserably up close. See Column C for an example of bump mapping.
Both displacement mapping and bump mapping have their uses. Bump maps are generally fast and require little resources. Displacement mapping requires more resources during setup and manipulation, but since this takes place during your scene setup, displacement mapping doesn't often increase your render time. Bump mapping will increase render time, as there is another shader to process.
Some uses of Displacement Mapping:
- landscapes
- animating fields of grass or trees
- waves or ocean water (and animating it)
- animating fire, clouds, smoke, or any other particle-driven volume
Some uses of Bump Mapping:
- adding realism to textures (human skin, orange peel)
- adding small details to an object
- simulating grass from far away
If anyone has any questions, or would like to add to this information, please feel free to do so! =)
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