There are two common approaches for making a material look bumpy when using most 3D rendering programs. These are “bump” mapping and “displacement”. A bump map makes a surface look as though it has high and low areas based on how light strikes the surface. Whereas displacement actually creates new geometry based on your model.
Below are two planar surfaces which have each been assigned a reflective material.
A procedural “noise texture” will be used to give one surface a bump map and the other displacement. Noise textures are often installed by default in render engines and come in a variety of types, this style is called “Perlin”.
The grayscale values in the image are used by both bump and displacement to create peaks and valleys and as a result, give the flat surfaces a physical texture. The difference is that the displaced version is truly no longer flat. Look at the edges of the surface on the right to see how they undulate compared to the bump mapped version which remains flat along the edge silhouettes.
Bump maps will also have a limit on just how three dimensional they can look. Usually this value is set in percent with 100% being the maximum amount. The reflection value a material has can aid in the effect but for the extreme appearance of bump, displacement should be used. In this way, the white values in the source image can be assigned a physical height as shown in the image below where they are now raised by a value of twenty units in the model.