Talk:Dot crawl

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It would be useful to have a discussion of SECAM here, which presumably has its own distinctive colour/luminance artifacts.

Anyone has a screenshot of the effect?

[edit] Confused

"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 causes high-frequency chrominance detail at color transitions to be interpreted as luminance detail" -- nope, it's the other way around (high-bandwidth luminance is indistinguishable from chrominance in a composite video signal). —Preceding unsigned comment added by 84.137.243.218 (talk) 19:47, 31 May 2008 (UTC)

[edit] Need Images

A still or animated GIF of dot crawl would be helpful for readers.

Dot crawl isn't the reason why fine detail suits are avoided on TV. The real reason is the frequency inversion phenomenon that appears when sampling a signal at a frequency lower that the bandwidth of the signal (Nyquist). It typically generates moiré patterns.

The dot crawl effect also happens with SECAM and NTSC. In SECAM, the dot crawl effect gets worse, it undulates both horizontally and vertically, making it look like it goes round in tiny circles counterclockwise. In NTSC, the visuals are very similar to that of PAL, but instead of seeing pixels running down, they are running up.