What is dot crawl??

Tomdale

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Can somebody please expalin what dot crawl looks like?
 
neilmcl said:
If you google it you can get loads of links to information.

what i did :)
 
The first link is not dot crawl in the AV sense of the word.

A lot of people ask this and very rarely is there a good example. So for you I've made one myself:

dotcrawl.gif


This is from a TV show that was mastered on Composite NTSC broadcast tape. You can see the 'crawling dots' because the equipment hasn't done the best job of seperating the yellow area from the purple background. This is because Composite video sends the Brightness and Colour information down one cable and relies on the TV to do the separation.

Composite video isn't a lost cause. Some Comb Filters (most notably I've been impressed by the ones the Sony WEGA sets have) clear the dot crawl up very well. But obviously, using a signal type that had the Brightness and Colour seperated in the first place, like S-Video, RGB, or Component, would save the TV this job:

dotcrawlnone.jpg


Note that for PAL video, the crawling dots appear much smaller. But, this also seems to make them harder for the Comb Filter to remove.
 

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