You can select a bitmap file or to control the Anisotropy parameter. The map controls the shape of the anisotropic highlight, roughly (but not necessarily) within the area specified by the glossiness parameter. Black and white values have little effect. Maps with a good deal of grayscale values, such as or , can be very effective.
Mapping anisotropy. The stretch of the highlight depends on the level of gray in the map.
Reducing the Amount of the anisotropy map reduces the map's effect, and increases the effect of the Anisotropy value on the Basic Parameters rollout. When the Amount is 0 percent, the map isn't used at all.