The dot crawl is the popular name for a visual defect of color analog video standards when signals are transmitted as composite video. It consists in animated checkerboard patterns which appear along vertical color transitions. It results from intermodulation or crosstalk between chrominance and luminance components of the signal, which are imperfectly multiplexed in the frequency domain. Composite video is the format of an analog television signal before it is modulated onto an RF carrier. ... Intermodulation or intermod is the result of two radio signals of different frequencies being mixed together, forming additional signals at frequencies that are not at harmonic frequencies (integer multiples) of either. ... In telecommunication, the term crosstalk (XT) has the following meanings: 1. ... Chrominance (chroma for short) comprises the two components of a television signal that encode color information. ... The word luminance, a synonym for luminosity, means emitting or reflecting light. ... Multiplex is either a word derived from multi- + plex (fold) or a synthetic portmanteau combining the words multiple and complex and can be another word for many or (literally) manifold. ... Frequency domain is a term used to describe the analysis of mathematical functions with respect to frequency. ...

Dot crawl only appears when the luminance is transmitted with a high bandwidth, so that its spectrum reaches the band of frequencies used by the chrominance signal in the composite video signal. In other words, it appears when "too much detail" is transmitted. The noun spectrum (plural: spectra) has a variety of meanings. ...

Another, similar problem is the appearance of a colored noise in image areas with too much detail. Television studio guests usually have to avoid clothing where too fine patterns appear on clothes, eg. ties.

Dot crawl was first widely noticed with the Laserdiscs. Pioneers LaserDisc Logo The Laserdisc (LD) was the first commercial optical disc storage medium, and was used primarily for the presentation of movies. ...

It can be removed using a comb filter in the receiver. In signal processing, a comb filter adds a slightly delayed version of a signal to itself, causing phase cancellations and a spectrum that looks like a comb. ...