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Colourblind (deficiency) and the rainbow effect

Discussion in 'TVs' started by Lord Biggington, May 17, 2005.

  1. Lord Biggington

    Lord Biggington
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    Perhaps a weird question, but I have been trying (unsuccessfully) to find information on the rainbow effect on these DLP sets for people like me who are colour blind (red/green colour blind). I have spent heaps of time in front of various ets in comet/currys etc and have yet to see any rainbows, was hoping I wont ever, perhaps due to my colour blindness (or deficiency).

    Anyone heard any info on this or are colour blind and seen rainbows?

    I realise for non colour blind people this may sound a weird question! :)
     
  2. supermackem

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    I might be able to help you out. I am like you colour wise and i havent spoted a rainbow in 2 months of veiwing the tosh. You might be right being colour blind might have its first advantage :)
     
  3. LV426

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    The three primary colours for addition (and hence used in all? colour display technologies) are red, green, and blue. It does seem hugely probable that, if you can't discern (well) the difference between two of these, your susceptibility to rainbows will be diminished or nil.

    Do bear in mind, though, any family members, etc., who may share your new TV with you.
     
  4. evolution400

    evolution400
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    I am colour blind and I also cant see rainbows :)
     
  5. Lord Biggington

    Lord Biggington
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    Thanks for that.
    As LV426 says just need to worry about the other members of the family now. :thumbsup:
     
  6. poldoc

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    I am red/green colour blind and after 4 Sagem Axium 50" TVs I can say I never saw a rainbow.....on my last set I never saw anything after the engineer had 'upgraded' it....but thats another tale for a different forum
     
  7. Razor

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    Interesting subject, are there any reports on this topic in mags or net?

    :)

    BTW I have a friend who is colour blind and he hasnt mentioned the rainbow effect once.
     
  8. supermackem

    supermackem
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    wooot go us colourblind people. lol anyway i think you have your answer mate dont look like us colour blind people can see them.
     
  9. NWhiteley

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    just a quick update on this.... i have just spent a couple of hours watching a HDD45 and a SP50 side by side (in currys, just for experiments sake), and i am also red/green colour blind. i tried everything possible to produce the rainbow effect but had no luck.
    i may now get one of these DLP sets instead of the plasma ive been looking at for a couple of weeks
     
  10. Mark_a

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    As a matter of interest, has it been clearly established just what the rainbow effect really is? Is it genuinely there all the time and just isn't noticed, or does it flick in and out of existence in such a way that only certain circumstances reveal it? Is it actually really present so it could be, say, photographed, or is it a set of unfortunate visual happenstances that just make it appear in someone's visual system? In other words, is it physical or physiological?

    Regards

    Mark
     
  11. Nick_UK

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    It has been clearly established. It's there because the colour information is being provided sequentially by a colour wheel. I suppose a long time exposure might show it in a photograph. The fact that in some people see it more than others is down to the persistance of vision, which is what enables us to see a moving picture in the first place.
     
  12. Mark_a

    Mark_a
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    So it's there permanantly, all the time, under all conditions, as a direct result of the technology? It just isn't noticed by most folks, most of the time?

    Regards

    Mark
     
  13. LV426

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    Exactly. The image thrown by a single-chip DLP is a rapidly repeating sequence of (maybe in another order) an all RED image, an all BLUE image, and an all GREEN image. At no time is a full colour image produced. Human perception merges the primary colours to produce full colour - in some people, better than others.
     
  14. meva

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    I'm slightly red green deficient ( protanomolous ) and see rainbows on dlp front projectors.
    I really don't think colour perception will make any difference to dlp induced headaches unless ( possibly ) you are completely colour blind.
    I am , incidentally , an Optician and must do some research on this topic.
     
  15. poldoc

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    After getting rid of my 4 Sagem Axia(plural of axiums) I invested in a ThemeScene H57.....still no obvious rainbow effect and WHAT A GREAT PICTURE.
    Mike
     
  16. Mark_a

    Mark_a
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    Sorry to harp on about this, but it seems to me that, yes, the technology sends a stream of discrete monochrome images up on the screen so fast that human persistance of vision merges them into a full colour display. But, that still doesn't explain what the 'rainbow effect' itself is. Is it the human persistance of vision behaving differently from person to person? If so, then there's no way you could photograph the effect because the effect is not a physical thing, it's a particular human's perception of a physical thing that defines the 'rainbow effect'. Or am I missing something?

    Regards

    Mark
     
  17. Gregory

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    Hi all,

    My two penn'oth - Care is required in drawing conclusions - few people are colour blind & even fewer have an issue with rainbow effects - so that a small sample shows no overlap demonstrates nothing - you'd need to do a huge sample or some other test to establish this - or work out the mechanism in the eye by which the rainbow annoys & show why specific colour blindness would 'correct' for it. Neither of these is done, so I would call it simply an interesting conjecture at the moment

    Ah - and to the last post, eye movement is normally part of the issue, so yes, photographing it is hard

    Cheers

    Greg
     
  18. LV426

    LV426
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    The rainbow effect arises (in those so affected) typically when there is contrast in the image, and when something (*) causes your eye to pan across the screen. As you pan, the intermittent nature of the colour becomes fleetingly visible. It appears as a rainbow trailing the edge of contrast.

    It can be photographed - at least, I've seen a bit of camcorder footage which demonstrated it. I guess you could probably get a still, too, but you'd need to either use a fast shutter speed, or a slower shutter speed and move the camera as you take it.

    (*) such as - a moving object you are following; simple panning a wide screen image (most likely on a front projection system due to the larger angle of view); or perhaps simply reading subtitles; etc.
     
  19. Mark_a

    Mark_a
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    I would have thought photographing it was impossible as a fast shutter would just get one of the monochrome images, and a slowed shutter would get some half-way merged effort that would be a composite of one monochrome image giving way to the next, the degree of which being a matter of timing.

    Now if eye movement is a critical part of the puzzle then that would seem to indicate that the brain is picking up one, or more, of the changeovers between monochrome images. Presumably the eye is moving from one part of the screen faster than the colour changeover and so at one point sees say a red image but as it moves to a new location and now sees a green image. But why this would result in a rainbow effect is still a puzzle to me, as that process is the same as what it's doing all the time when you don't see the rainbows.

    Regards

    Mark
     
  20. Mark_a

    Mark_a
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    Never seen it myself, but then I don't get my Tosh 52" till tomorrow and I bought it unseen. So what you're saying is if you were to generate on a PC, or animate on film, a simple white box and slowly bounce it around a black screen, and stared straight ahead, and didn't follow the path of the square, you wouldn't get the rainbow effect as it passed in front of your line of sight? But if you tracked it around the screen you would see it all the time?

    This would seem to indicate that the eye/brain is not processing in an analogue fashion as it wouldn't see a steady rainbow, but instead a sequence of colour changes depending on how fast the screen is updated, how fast the colour is changing, and how fast the block is moving. Presumably the effect becomes more noticable on a larger screen? Does this mean DLP projectors increase the speed of their colour wheels, compared to RPTVs, to combat this?

    Intriguing stuff.

    Regards

    Mark
     
  21. NicolasB

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    Basically right. But remember that when you are watching any kind of video, you're not watching a moving picture: you're watching a sequence of still frames. So the whole concept of video depends on being able to see something that isn't actually there: actually it's a sequence of still pictures, but your brain interprets it as motion.

    In the same way, any single-chip DLP device is not actually a sequence of multi-coloured frames, it is a sequence of red frames, green frames, and blue frames, and the brain combines these together to produce colour and motion. In fact, you aren't even actually seeing pixels of variable brightness: you're seeing pixels of fixed brightness that flash on for varying lengths of time within the duration of the frame.

    So it's not very sensible to try and talk about "what's there" and "what you see" as two separate things. "What you see" is all that matters. As you say, the rainbow effect happens when the red, green and blue sub-frames of the same full frame end up in different places on the retina because of eye movement.

    Speeding up the colour wheel means that there's less of an interval between successive R, G and B images, and therefore less of a chance that the brain will interpret them as distinct. Using a 3-chip DLP system (as found in high-end projectors) eliminates rainbows entirely because there the R, G and B components of the image are all on the screen simultaneously. But this is much more expensive, and, of course, there can be other problems (e.g. convergence).
     
  22. Razor

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    Well put Nicholas B :thumbsup:
     
  23. LV426

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  24. poldoc

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    Still can't see it.........seasick tho'!!
     
  25. Caimbeul

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    Its interesting to note that all mags still refer to the sets as producing the rainbow effect. They never mention that its down to the individual. Do they even know :confused:
     

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