moire-type pattern on black screen

Discussion in 'Displays' started by DaveKahler, Apr 7, 2003.

  1. DaveKahler

    DaveKahler Stunt Coordinator

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    When the tv is very dark (most noticeable on total blackout), there is a horizontal moire-type pattern that's really annoying me. You can see the lines especially during scene changes. It's most noticable when the tv is just in a blank a/v mode, though.

    Any ideas on how to fix this? I've tried disconnecting all inputs, and it's still there.
     
  2. Allan Jayne

    Allan Jayne Cinematographer

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    Can you describe it in more detail?

    Try turning the contrast way down and then turning the brightness way up for just a few moments with no cables connected in back. This may make the moire pattern easier to see.

    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  3. DaveKahler

    DaveKahler Stunt Coordinator

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    It's horizontal lines, at about the middle 2/3 of each side of the screen, that converge toward the center of the screen. They also tend to be visible only near the edges, i.e. they pretty much disappear about 5-7" away from the sides. I have a panansonic 27SX12 27" flat screen, by the way.
     
  4. Allan Jayne

    Allan Jayne Cinematographer

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    The shadow mask in the picture tube may have a horizontal line structure. Usually the phosphors are in long thin vertical red, green and blue stripes. Except for Sony's, there are thin horizontal bridges that connect the vertical ribs of the shadow mask and you can see them using a magnifying glass while viewing a medium gray solid "test pattern".

    If the scan lines clash with this bridge pattern, you get these moire patterns. The moire is often accompanied by pincushion distortion and otherwise not quite straight and level scan lines.
     

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