Dot crawl defintion?

Discussion in 'Archived Threads 2001-2004' started by Ryan Wesson, May 21, 2001.

  1. Ryan Wesson

    Ryan Wesson Auditioning

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    I have seen the term "dot crawl" used a few times in the forums. Could someone please try and define what this refers to? [​IMG]
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  2. Jack Briggs

    Jack Briggs Executive Producer

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    Ever notice how, when you look at a brightly colored object on the screen that's situated next to something not so brightly colored, there seems to be movement along the objects' borders, sort of like bubbles in a fish tank? Those are NTSC interlacing artifacts, known as "dot crawl." It's called "dot crawl" because that's what it looks like. Dot crawl is reduced somewhat by a good comb filter. To eliminate it altogether, think component-video input and progressive scan.
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  3. Jay Mitchosky

    Jay Mitchosky Producer

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    If you want to see it connect your DVD player to your TV's composite video input and bring up the color bars pattern from Video Essentials or Avia. Depending on the quality of your TV's comb filter you will see a "freeway" of dots rising up and down (like bubbles) where the different colored bars meet. Another good test is the Video Essentials' Montage of Images. The yellow parking polls are nasty. And the scene where the two dancers are nose to nose against a blue background - you'll see a mass of smeared dots outlining their faces. This shows how much dot crawl and hanging dots can reduce the sharpness and detail of an image.
    It's a function of the comb filter's inability to properly separate the luminance and chrominance information (black/white and color). Newer sets typically have very good comb filters so you may not see this effect at all. As Jack indicates it will not be an issue for you if you are using S-Video or Component connections for DVD. Where you will see it is from your VCR (depending, again, on the TV's comb filter).
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  4. derek

    derek Second Unit

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    This month's Sound & Vision magazine has a good introductory article to various video transmission types (composite,svid,component) along with some good pics including dot crawl.
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    Derek
    Surround EX FAQ: http://www.geocities.com/Heartland/P...urroundex.html
     

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