Dither is an intentionally applied form of noise used to randomize quantization error, preventing large-scale patterns such as color banding in images. Dither is routinely used in the processing of both digital audio and video data and is often one of the last stages of mastering audio to a CD.
A common use of dither is converting a greyscale image to black and white, such that the density of black dots in the new image approximates the average grey level in the original.
Dither is utilized in many different fields where digital processing and analysis are used. These uses include systems using digital signal processing, such as digital audio, digital video, digital photography, seismology, radar and weather forecasting systems.
Quantization yields errors. If that error is correlated to the signal, the result is potentially cyclical or predictable. In some fields, especially where the receptor is sensitive to such artifacts, cyclical errors yield undesirable artifacts. In these fields introducing dither converts the error to random noise. The field of audio is a primary example of this. The human ear functions much like a Fourier transform, wherein it hears individual frequencies. The ear is therefore very sensitive to distortion or additional frequency content, but far less sensitive to additional random noise at all frequencies such as found in a dithered signal.