Chroma dots

Chroma dots are visual artefacts caused by displaying an unfiltered analogue colour video signal on a black-and-white television or monitor. They are commonly found on black-and-white recordings of television programmes originally made in colour. Chroma dots were once regarded as undesirable picture noise, but recent advances in computer technology have allowed them to be used to reconstruct the original colour signal from black-and-white recordings, providing a means to colourise material where the original colour copy is lost.

Background

Analogue colour video signals comprise two components: chrominance and luminance. The luminance component describes the brightness of each part of the picture, whilst the chrominance component describes the colour tone. When displayed on a black-and-white monitor, the luminance signal produces a normal black-and-white image, whilst the chrominance signal manifests as a fine pattern of dots of varying size and intensity overlaid over the black-and-white picture. A related phenomenon is dot crawl, which can produce visual artefacts in colour pictures.