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How manufacturers could eliminate the RBE...maybe...

Discussion in 'Projectors, Screens & Video Processors' started by Bugblatter, Sep 1, 2005.

  1. Bugblatter

    Bugblatter
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    Ok, I was thinking about the RBE and came up with an idea for pretty much eliminating it even with a colour wheel. I'm guessing there's a flaw in my logic, otherwise they'd already have done it, but I can't see the flaw.

    Ok, the magic solution is to add a clear (white) segment to the colour wheel.

    RBE is noticeable when you get strong white against strong black. That's because the white is made up of red, green and blue. Well why not make the white up from white?

    Ok, it may not be pure white. Fine, so make most of it from white, and add a little red or whatever. So if you have a colour with an RGB value of 222, 245, 255 then use a white value of 222 plus a red value of 0, a green value of 23 and a blue value of 33. There's no reason to only do this for bright colours, any colours could use white up to the lowest of the red, green and blue, and make the rest up with the other segments.

    I read that some cheaper DLPs already have a white segment to improve the brightness. Perhaps that means there's some way that having a white segment affects quality (perhaps it reduces contrast), otherwise they'd all be doing it.

    Ok, so tell me why it's a lousy idea :D
     
  2. Gary Lightfoot

    Gary Lightfoot
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    Some people who see RBE have said that a brighter image makes it more noticable, so the added brightness of a white segment tended to make it worse. I see your point about using one, but it seemed to have the opposite effect. The negative aspect was that the clear segment tended to wash out the colours so they would appear less saturated that a similar PJ without the segment (try taking a flash photograph of a projected image on a screen and you get the idea). For good colour reproduction you don't want the white segment, or at least black it out or turn it of like some pjs allowed you to do (Infocus 4800 IIRC).

    A few years ago there was an idea of using a colour wheel that had the colours laid out in a spiral fashion rather than in segments (sequential colour recapture??). I believe it was hard to program for, as all the colours were being reproduced on parts of the screen at the same time, but you had to take into account the way the archimes wheel arrangemnt of colour was moving across the screen. So far it hasn't appeared in any production models as far as I know.

    I think the only way to eliminate RBE is to use 3 chips like the latest Sim2 C3X. if there was a way to remove it from single chip DLP then I think TI or a pj manufacturer would have found it by now.

    Gary.
     
  3. Bugblatter

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    The image wouldn't necessarily be any brighter, the DLP chip can control that, and anyway the RBE should be virtually eliminated as the bright parts of the picture are made from white rather than a combination of red, green and blue. There might be a small amount of those colours present to provide the right tint, but nowhere near enough to cause the RBE.

    Maybe those cheap DLPs just weren't using the white segment in the way I'm suggesting, or they looked crap because they were cheap.

    I don't get the thing about flash photography though, when the white segment's in place the DLP would only be letting through the right amount of light, which is the same amount as the red, green and blue segments would have let through combined.

    I agree that there's probably a reason why it doesn't work, but I'm not seeing it.

    Hey, what time does the patent office open? :-D
     
  4. Gary Lightfoot

    Gary Lightfoot
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    The image is brighter because the RGB segments cut light and there's nothing the DMD can do about that since thay can't be made any more reflective. Coloured glass that let more light through without reducing the saturation might have helped maybe but didn't seem to be used like the white segment was. Adding a white/clear segment meant that more light hit the screen and reflected off of it, but was being added to the RGB colours so reduced the saturation - each colour makes up and image and relies on persistance of vision for us to see the image as a colour and not as a flash of RGB. Adding white into the same frame will make it look brighter but less colourfull.

    The Infocus projector added a lot of lumens to the image by using a white segment, and that was useful for data projection such as PowerPoint presentations. For video it disabled the white segment which dropped lumens and contrast by quite a bit. (CR went down from an advertised 2000:1 to 1400:1 IIRC). Image quality went up though, and that's the aim for home theater.

    You should make a working prototype that proves the theory then get it patented and make lots of money as every DLP manufacturer would want it. :)

    Gary.
     
  5. NicolasB

    NicolasB
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    They already use white segments in colour wheels. But the usefulness is limited - a bright yellow, magenta or cyan object would still produce rainbows.
     

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