The randomness contained within a signal. Noise functions simulate various kinds of randomness found in real world signals. The two main types of noise functions are value and gradient noise. Each value in value noise is independent of its neighbouring values, thus this type of noise can only occur in discrete signals. In gradient noise the values vary smoothly, i.e. each value is related to the values in its immediate vicinity. In computing, noise is typically used to mimic natural effects, such as film grain, moss growth patterns or landscape heights.