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Green dotty noise

Discussion in 'Projectors, Screens & Video Processors' started by Mark13, Jan 11, 2005.

  1. Mark13

    Mark13
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    I recently bought a Sharp XV-Z91E Projector and I am generally very impressed with the picture quality. However occasionally I have noticed the presence of an odd appearance where there is some greenish speckling over dark areas. I noticed it particularly on the underwater submarine sequence in The Phantom Menace.

    According to the projector magazines this is a problem that is common to DLP machines. I find this more of an irritation than the oft mentioned rainbow effect which to me is hardly noticeable.

    I am currently projecting onto a magnolia wall and I wonder if this is adding to the effect. I am considering buying a screen but I am unsure as to whether it will make any difference.

    Any thoughts?
     
  2. Oakleyspatz

    Oakleyspatz
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    How are you connecting your source to your projector? If you are using just composite or even S video, moving up to component will help. Dot crawl is a problem caused by poor chrominance(colour)/luminance(brightness) filtering. Component as does RGB, helps correct this problem by seperating the colour/luminance filtering. If you are connecting via one of these and still get this problem, it may well be just a limitation of this particular model. As you mentioned, earlier and newer lower priced DLP projectors can suffer from a green dot crawl although The latest batch of DLP models such as the Infocus 4805 have addressed this problem successfully with superior video processing.
     
  3. Mark13

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    I am currently using an S-video cable. Sadly my DVD player doesn't have a component output. Perhaps my next upgrade will be a new DVD player.

    Thanks for the advice.
     
  4. Bristol Pete

    Bristol Pete
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    Try reducing the contrast to minimise the green dot crawl.

    Cap :)
     
  5. Gary Lightfoot

    Gary Lightfoot
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    Actualy, you should reduce brightness for black level, and contrast for white level. :)

    This could well be an incorrectly set brightness level (or gamma setting) as Cap has suggested, as seeing mpg artefacts is one of the results.

    As it's a DLP, it could be the green is more active at a certain dark level, though I doubt you'd see this from a normal seeting position.

    To correctly set your brightness and contrast for DVD, you should use something like Video Essentials (for PAL) or Avia (for NTSC). If your DVD player has a 0ire or some similar black setting for NTSC, use it, as that will set both black levels for PAl and NTSC to the same level.

    Another way is to go up to the screen when playing a 2.35:1 movie, and adjust the brightness down until you can no longer see any mirror activity occuring in the black bars. They will look like tiny white dots or 'mosquito noise' flicking around. It's not a perfect way to do it, but it does work quite well sometimes.

    HTH

    Gary.
     
  6. Bristol Pete

    Bristol Pete
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    See Gary, now you know why I always ask you questions...LOL

    Thanks for putting that right.

    Doh!

    Cap :)
     
  7. Gary Lightfoot

    Gary Lightfoot
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    No Probs,

    Easy mistake to make, and it was something I never even considered until I became aware of it myself. I always wondered what those controls were doing, because they both seemed to do much the same thing. :)

    Gary.
     
  8. Oakleyspatz

    Oakleyspatz
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    Just incase this is all fairly new to you, here's a brief description of the things we're discussing here. The thing to remember with any projector is the image is only as good as the weakest link in the chain. You may have a great pj, a great DVD player but if you connect them via a composite lead, you'll have artifacts appearing. Adjusting contrast and brightness may well mask these problems, but to really overcome them you should always try and improve on the weakest link.
    S Video is not a bad connection on a TV, but projectors displaying images of 7 foot across, show up it's limitations. RGB, Component or the latest DVI/HDMI should all be top of your list.

    Composite video
    A single video signal that contains luminance (brightness) and chrominance (color) information. A composite signal is better than an RF signal, but not as good as S-video or component video. A composite video jack is usually a single RCA-type.
    S Video
    this 4-pin connector usually provides a sharp, high resolution picture by transmitting the chrominance and luminance portions of a video signal separately. The signals can then be processed separately, reducing interference. Direct S-video connections generally outperform composite connections
    Component Video
    The three-jack component video connection splits the video signal into three parts (one brightness and two color signals). Component video has increased bandwidth for color information, resulting in a more accurate picture with clearer color reproduction and less bleeding. A growing number of TVs include component video jacks to provide the best possible picture quality (better than S-video or composite video) when connected to a compatible DVD player.

    Chrominance
    The color component of a video signal that includes information about hue (shade) and saturation (intensity).

    Luminance
    The brightness or black-and-white component of a color video signal. Determines the level of picture detail.


    Contrast ratio
    Measures the difference between the brightest whites and the darkest blacks a display can show. The higher the contrast ratio, the greater the ability of a display to show subtle color details and tolerate ambient room light.

    Artifacts
    Unwanted visible effects in the picture created by disturbances in the video transmission or processing. Examples include "dot crawl" or "hanging dots" in analog pictures, or "pixelation" in digital pictures.
     
  9. Gary Lightfoot

    Gary Lightfoot
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    Don't forget, that no matter how good your equipment is, having settings such as brightness and contrast incorrectly adjusted can make a good set-up look aweful. Then they won't be masking anything except unwanted artefacts that shouldn't be visible anyway, as they're below the normal level of black which you should be calibrated too. You'll just be seeing what you should be seeing. :)

    Having blacks as black as can be without masking shadow detail is one advantage, as is bright skys with cloud detail. Having grey blacks with noisy artefacts and bright skies with no cloud detail or overly bright highlights are some disadvantages, none of which can be cured with even the most expensive equipment.

    Having an optically adjusted colour wheel for the lamps RGB imbalance helps with colour accuracy (D65) more so than dark area dithering, though extra dark green segments will achieve this, but not many projectors have them. I personaly find that a correctly adjusted pj will show a great deal less dithering and dark area noise than a poorly adjusted pj with green segments.

    Gary.
     

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