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End of the rainbow?

Discussion in 'Televisions' started by Grobnic, Jul 29, 2005.

  1. Grobnic

    Grobnic
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    Guys

    I was browsing the web, as you do, and I came across an article on LCD v DLP (http://www.projectorcentral.com/lcd_dlp.htm). What catch my eye was the comments about efforts to suppress the rainbow effect on DLP TV's.

    Quote from the text on rainbows

    Texas Instruments and the vendors who build projectors using DLP technology have made strides in addressing this problem. The first generation DLP projectors incorporated a color wheel that rotated sixty times per second, which can be designated as 60Hz, or 3600 RPM. So with one red, green, and blue panel in the wheel, updates on each color happened 60 times per second. This baseline 60Hz rotation speed in the first generation products is also known as a "1x" rotation speed.

    Upon release of the first generation machines, it became apparent that quite a few people were seeing rainbow artifacts. So in the second generation DLP products the color wheel rotation speed was doubled to 2x, or 120Hz, or 7200 RPM. The doubling of the refresh rate reduced the margin of error, and so reduced or eliminated the visibility of rainbows for many people.

    Today, many DLP projectors being built for the home theater market incorporate a six-segment color wheel which has two sequences of red, green, and blue. This wheel still spins at 120Hz or 7200 RPM, but because the red, green, and blue is refreshed twice in every rotation rather than once, the industry refers to this as a 4x rotation speed. This further doubling of the refresh rate has again reduced the number of people who can detect them. Nevertheless it remains a problem for a number of viewers even today.


    I know this refers mainly to projectors, so my questions are...

    Has anybody come across this and has more info?

    Of the current generation of DLP TV's which ones have the fastest (x2 or x4) disks used in them?

    (I'm interested in the Sagem 45HD, but any info on 45 - 50 inch models would good)
     
  2. neilmcl

    neilmcl
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    All of the newer DLP models now have 7 segment colour wheels that spin at higher speeds but whilst this may reduce the effect because of the very nature of using a colour wheel rainbows can still be a problem for people that are susceptible. It won't fully disappear until you have a dedicated 3 chip colour system which is currently only available on the top-range of projection systems costing tens of thousands pounds.
     
  3. Tarbat

    Tarbat
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    The latest Samsung DLP TVs rotate the colour wheel at 10800rpm
     
  4. ayrshiredude

    ayrshiredude
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    I have the new Samsung 46" DLP and while the Picture is very good I can see the rainbow effect pretty much all the time, especially when I move my eyes across the screen.

    I was wondering though does the DLP chip have anything to do with how much you see this effect? I have looked at the Sagem 45" and don't recall seeing the rainbow effect so could the H2+ chip not be so obvious as the H4 is. I am going to look at it again though as I have perhaps just not looked att the screen long enough.

    Any ideas?
     
  5. neilmcl

    neilmcl
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    The chip really hasn't got much to do with the rainbow effect, it's all about how colour is "added" to the greyscale image via the spinning colour wheel that tricks the eye into seeing a colour image. I spent months looking at different DLPs and could have sworn that I didn't suffer from rainbows, it was only when I bought the Samsung SP46 and got it running at home under normal conditions did I start to notice them. In fact I've looked at various DLPs since including the SP46 in the stores and have barely seen a rainbow. If you have a problem with the Samsung I would doubt that any other make will be any different.
     
  6. Grobnic

    Grobnic
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    It's these sort of stories that make me nervous. I've spent a while in Currys looking at the Sagem 45HD and become more confused that ever. They actually had a good set up for once (until Comet) as they had a SD feed going through the Sagem (an old colorized movie) and I could stand back and view it at my normal viewing distance. The problem was it was between two other DLP TV's so when I flicked my eyes back and forth (the recommended approach to test for rainbows I think) I could pick up rainbows out of the side of my field of vision, but I could not work out which of the 3 TV's was causing this.
    It was probably all three, but I then ask myself if I will only see rainbows if I try really hard and in normal use I'll not notice them or am I one of the few who'll see them always.

    I've tried going to specialist shops with view setups but they all seem to look down their noses at DLP and insist on telling me I won't like it ("please buy this £4,000 plasma, it's better promise, cross my heart and hope to die").

    So I putting out questions on this forum and seeing what options are out there and I'll eventually take the plunge and buy. Until them keep your comment coming.

    Thanks for all the views so far.
     
  7. Ragnarok

    Ragnarok
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    i went to moth my local independant shops looking for a DLP demo. i asked a bout DLP in one and they basicly said whats that??

    The other really did know the score. a sagem hd45 on display and said plasma are good but if you want quality and not space saving then DLP is the way to go.

    Also the i found out i'm pritty imune to rainbows. :D :D :D
     

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