Help! Is there any way to minimice or avoid rainbow effect in DLP projectors?

Discussion in 'Archived Threads 2001-2004' started by AlbertAgullo, Sep 15, 2002.

  1. AlbertAgullo

    AlbertAgullo Agent

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    Thanks
     
  2. Gil D

    Gil D Supporting Actor

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    I notice the rainbow effect on my LT150 when I dart my eyes across the screen. Sitting further back from the screen may help with this since your eye movement is less to track the action on-screen. Also the newer DLP PJ's have a higher speed color wheel which is said to reduce the effect.

    I notice I get a similar effect from my RPTV by moving (darting) my eyes quickly across the screen. I see a flash (or memory of the image)of any bright image on the screen. Similar to looking into any light in darkness, and then looking away.

    Although I see the rainbow effect occasionally it doesn't bother me. No-one else in the family sees them and I didn't notice them at all for the first few months I had the projector. The DLP image from a front projector with a high contrast ratio is exceptional, especially hdtv.
     
  3. Neil Joseph

    Neil Joseph Lead Actor

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    Neil Joseph
    What kind of projector do you have?
     
  4. AlbertAgullo

    AlbertAgullo Agent

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    I have a PLUS U3-810-SF.

    Well, I imagined there was some sort of photographic filter to minimize it. I guess it does not exist.

    In fact I've discovered I can get use to it. If I concentrate enough...

    I read somewhere that it's more a PAL problem than a NTSC problem. Do you think progresive output could be better?
     
  5. Allan Jayne

    Allan Jayne Cinematographer

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    As far as I know, all DLP TV sets are progressive scan at the DLP chip, using a built in doubler for interlaced inputs. In the crudest sense, the red, green, and blue content holding areas (buffers; needed for single chip DLP and LCD systems) act as the doubler with just the even scan lines or just the odd scan lines replaced for each 1/60 second (NTSC) as each interlaced field arrives.
    Only reason PAL would have more rainbows is that PAL is fundamentally 50 frames per second (progressive scan) compared to NTSC's approx. 60 fps. In the simplest case each video frame is represented three times on the DLP chip, for red, green, and blue content as the color wheel spins which is slower for PAL. The better DLP units use still faster color disk rotation. I am not sure of the exact speeds, this depends on how fast the DLP chip can change picture content. I suppose it is possible for PAL to be presented using an effective 300 fps at the DLP chip, each frame repeated six times, two reds, two greens,and two blues. There are some PAL CRT TV sets that are advertised as 100 Hz refresh, the 50 fps progressive frames are each displayed twice. It doesn't have to be an even multiple, the PAL could be done with 200 fps, the first video frame used for red, green, blue, red on the DLP chip, the next video frame used for green, blue, red, green, and so on.
    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  6. Chris PC

    Chris PC Producer

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    If you are using an HTPC is there an ideal refresh rate that minimizes the Rainbow effect? (Has to be within the range of compatible refresh frequency rates of the projector of course)
     
  7. Max Leung

    Max Leung Producer

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    I'd like to know this too (Chris' question).
     

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