Dot crawl
It consists of 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. This takes two forms: chroma interference in luma (chroma being interpreted as luma), and luma interference in chroma. Dot crawl is most visible when the chrominance is transmitted with a high bandwidth, so that its spectrum reaches well into the band of frequencies used by the luminance signal in the composite video signal.This results from high-frequency luminance detail crossing into the frequencies used by the chrominance channel and producing false coloration. Dot crawl can also make narrowly-spaced text difficult to read. Dot crawl has long been recognized as a problem by professionals since the creation of composite video, but was first widely noticed by the general public with the advent of Laserdiscs. Dot crawl can be greatly reduced by using a good comb filter in the receiver to separate the encoded chrominance signal from the luminance signal.
Dot crawl is the popular name for a visual defect of color analog video standards when signals are transmitted as composite video, as in terrestrial broadcast television. However, the only complete solution to dot crawl is not to use composite video, maintaining the signals separately by using S-Video or component video connections instead. Monochrome film recordings of colour television programs may exhibit dot crawl, and starting in 2008 it has been used to recover the original colour information in a process called colour recovery. .
This causes high-frequency chrominance detail at color transitions to be interpreted as luminance detail. The opposite problem, luma interference in chroma, is the appearance of a colored noise in image areas with high levels of detail.
