Dither
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 processing of both digital audio and video data, and is often one of the last stages of mastering audio to a CD.
For other uses, see Dither (disambiguation).A common use of dither is converting a grayscale image to black and white, such that the density of black dots in the new image approximates the average gray level in the original.
Etymology[edit]
The term dither was published in books on analog computation and hydraulically controlled guns shortly after World War II.[1][2][nb 1] Though he did not use the term dither, the concept of dithering to reduce quantization patterns was first applied by Lawrence G. Roberts[4] in his 1961 MIT master's thesis[5] and 1962 article.[6] By 1964 dither was being used in the modern sense described in this article.[7] The technique was in use at least as early as 1915, though not under the name dither.[8]
In digital processing and waveform analysis[edit]
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 error. 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.[9][10] 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.[11]