Dot crawl

It results from intermodulation or crosstalk between chrominance and luminance components of the signal, which are imperfectly multiplexed in the frequency domain.

[1] Some (mostly older) video-game consoles and home computers use nonstandard colorburst phases, thereby producing dot crawl that appears quite different from that seen in broadcast NTSC or PAL.

The effect is more noticeable on these cases due to the saturated colors and small pixel scale details normally present on computer graphics.

[citation needed] The opposite problem, luminance interference in chroma, is the appearance of a colored noise in image areas with high levels of detail.

When the NTSC standard was adopted in the 1950s, TV engineers realized that it should theoretically be possible to design a filter to properly separate the luminance and chroma signals.

[6] This type of filter uses a computer to analyze the NTSC signal three scan lines at a time and determine the best place to put the chroma and luminance.

Enlarged detail from a video source exhibiting dot crawl. Note the distinctive checkerboard pattern on the vertical edges between yellow and blue areas.
RAI Philips test card with artifacts visible in areas of contact between solid colors (ex: yellow and cyan) and on high horizontal detail ("rainbows" over fine vertical stripes pattern) - click to enlarge