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i see rainbows as small areas, about 3 inches long and about 1 inch wide.

they flash for about 1/2 second and are gone.

sometimes it is as if they are just in the corner of my eye.

they never are large areas of the screen and they never last long.

they almost look like the rainbows that come off of the

small prisms that were popular in the 70s.

so for the people who do see them, do they look to you

the way i describe? and even more bizarre, what if not only

do some people see them and some dont, what if some people

see them in a whole different way than others?
 

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I see them across the whole screen. For example, if there is a scene with white areas against a dark background and I move my eyes, all of the white turns into a red/green rainbow.
 

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The rainbows I see appear to be a mile or so long and go across the sky usually after a rain
 

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Here is my attempt at showing what my LT150 looks like, as compared to my JVC G11 or Hitachi 5500. The Hitachi/JVC is on the left and the LT150 one-chip DLP is on the right.


I tried not to exaggerate at all, and you should see that the effect is quite subtle. In fact, some people may not see the rainbow at all :D.

http://www.colorfacts.com/colorfacts/images/3dlp.gif http://www.colorfacts.com/colorfacts/images/1dlp.gif


That's about the best I could do on and present it on the screen. The effect is more subtle that this in person.


Mark
 

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Lol.That's pretty good milori.The sad part is that the Yamaha at my local dealer actually looks like that to me.
 

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I saw my first dlp pj last thursday and the rainbows I saw were around white objects on a dark background and also around the entire picture, even if the section was dark and had no real bright objects in it. It was very weird and looked bad.
 

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Snakeman:


Didn't I just read a thread critical of Piano, where you pointed out rainbows all over the place? Now you are trying to clarify what rainbows look like? Shouldn't you have clarified what rainbows look like before you use the term to describe a problem with the Piano?


Ron
 

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Milori, thats exactly what I use to see. But I never see rainbows anymore.
 

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Quote:
Originally posted by rlindo
I saw my first dlp pj last thursday and the rainbows I saw were around white objects on a dark background and also around the entire picture, even if the section was dark and had no real bright objects in it. It was very weird and looked bad.
That is the first time I have ever heard anyone describe a rainbow in anything other than a high contrast scene. Could have been a problem with color wheel sync.
 

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I first noticed them on a black/white movie with lots of action... looked just like the above example... not good.
 

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I'm sure this has been discussed before, but my quick search didn't find it:


What exactly is the source of these rainbows?


I guess the question becomes more a question of how the DLP with color wheel works. I'm guessing the situation is as follows, but please correct me if I am incorrect:


Every 180th of a second, a new color wheel segment (R, G, or B) moves over the DLP chip. The DLP chip holds its pixels in one configuration for the length of that 180th of a second, and then changes to the next configuration as instantaneously as possible for the next 180th of a second. There is no time in between where the DLP mirrors temporarily switch to their "black" state. So as the color wheel transition from one color to the other is sweeping across the DLP, the pixels in the DLP are changing configuration to the new values for that new color value.


The problem is that the switching of the mirrors isn't precisely synced with the switching of the color wheel. There could be several reasons:


- The mirrors have mass and can't change states instantaneously, so they are "in motion" between states as the color wheel transition passes over them.


- The algorithms driving the mirrors might not be as smart as they could be. Since it takes some time for the color wheel transition to sweep over the DLP surface from one end to the other, ideally the pixel transition would be phased, starting at one end and moving towards the other end, synced up precisely with the color wheel. Presumably lower cost projectors just transition the whole DLP chip at once, which ends up not matching the color wheel.


- There might be some "flutter" of the mirrors, from being jarred as they move; it may take a little while for them to settle and stabilize. I'm not sure just how they are controlled, if they are servo-controlled, whether there is any active braking or other optimizations so that the momentum of the movement doesn't cause them to overshoot the desired position.


Thinking about this, I suppose what I'm most curious about is why this problem only occurs with DLPs. I would assume that LCDs would suffer from the first two issues above, but yet we don't hear of rainbows with color wheel LCDs.


At any rate, it sounds like some partial solutions to this problem would include:


- having black sections on the color wheel in between R, G, and B, to give the mirrors time to make their transitions.


-"Predictive" algorithms which would adjust pixel values to compensate for the amount of "slurring" between color wheel transitions. For example if displaying an image of 80% Red, 50% Blue, 0% Green, the computer might realize that the Red light output will be reduced during the G->R transition and the R->B transition, so it might actually set the Red pixel value to 85% to compensate.


-Tom
 

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Milori,


That is ingenious how you made those rainbows. Very fancy.


By the way, I see the exact same thing when I watch DLP. I find the effect to be worse when I'm extremely tired also. A shame for me, because I really love the smooth look of DLP.


Brett.
 

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I'm using Milori's picture as my windows wallpaper... hopefully after a few weeks of staring at it I can make myself immune to seeing them. I will start with 12 advil a day and work my way down. :p
 

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Tom Morrow,

Very good post, I am also not really sure of how DLPs work so the following is just my guesswork.


I don't think that rainbows are associated with the mirrors at all, and I don't think that smarter algorithms or faster mirrors will fix the rainbow problem. The problem is that at any one moment you are displaying a full screen of exactly _one_ color. The slower the color wheel the greater amount of time that that one color is on screen. Creating a picture by "flashing" one color at a time works great as long as the image is static, but when there is rapid movement in the screen or the viewer is changing his viewing position... you get the idea.


I would put all of the possible problems associated with controlling the mirrors under a different category, some people claim to see artifacts or "swarms".


The reason there are no rainbows with lcds is that there is no such thing as a "color wheel lcd"


LCDs have stacked color panels and you shine a light through them. The difference is that LCDs will not have rainbows, they will not have motion artifacts of any kind and will have better colors and brightness than comparably priced DLPs, instead they have serious screen door and low contrast issues.


LCOS has all of the strenghts of LCDs without screendoor problems and with much better contrast, making it the technology to bet on for the future in my opinion, at least untill three chip dlps enter the same price range.
 

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Tom Morrow --


Even if algorithms and mirror motion was perfect, some people will still tell colorwheel artifacts with a 180 Hz colorwheel. The faster the colorwheel moves, the harder to detect rainbows. If there is movement and your eyes are moving, there is always danger of rainbows with at least some people. There's a law of diminishing returns with faster colorwheel speeds, but even with 6X colorwheels, we still haven't 100% eliminated rainbows.


In certain situations, people will still be able to tell discontinuity at ricidulously high frequencies. An example is a 600 Hz light source if the motion was fast enough. Imagine a very bright 600 Hz strobe light that's moving 600 inches per second horizontally across your field of vision while you are staring stationary ahead. It will leave a dotted light path with flashes 1 inches apart rather than a continuous blur path (as would be for a continuously shining light source). 600 Hz divided by 600 inches, would mean the light is flashing every 1 inch. So, in this extreme case, you can tell that a 600 Hz light source is flickering rather than steadily shining. This is also additionally, easier to notice, the stronger the light source is. An extreme case is if the light source is strong enough to temporarily burn into your vision temporarily (like it sometimes occurs when you stare into a camera flash). Basically, the higher the frequency, the faster the light source has to be moving before you can notice discontinuity in its illumination. One actually does not need to be sensitive to flicker to see this type of motion-discontinuity, since you are only observing a side effect from the flicker indirectly and not the flicker itself directly.


This translates to DLP projectors too in helping to explain why rainbows occur with some people -- especially when some people roll their eyes around (ie, white breaks up into a rainbow of colors). For some people, the faster the eye movement, the easier it is to see the rainbows. And fast action scenes containing extreme contrast (like torches or lights on black backgrounds) will help make it easier to see rainbows, since rainbows does tend to be easiest to observe around the edges of objects against dark background. For other people, they see rainbows all the time just simply by staring at the image (i.e., people whose flicker sensitivity is ultrahigh).


Sensitivity to rainbows varies from person to person for many reasons (Just a few, includes sensitivity to flicker, to their eye movement speed, the way the person tracks their eyes on a moving object on the screen, ambient conditions, the way their brain processes non-continuous images, etc).
 

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Snakeman and others:

At last I have an answer to a somewhat more well-defined question that has bothered me WAY too much - "What's all this "Rainbow" business, then?"

As a Plus Piano owner, I believe I can now definitively state that I have never seen a rainbow, other than the type referred to by Jonmx. I have seen some "crawlies" from time to time during fast panning of a large blocks of color, such as a wall or a monochrome sky, but nothing resembling milori's rendition of the rainbow phenomenon. I think what I notice are "motion artifacts", and as I and others have said, I bet I won't see them as long as I watch the movie, not the PJ.


I have never been dizzy (well, not because of my projector), got a headache, passed out, or had any of the ill effects that some attribute to the viewing a DLP projector. I always assumed that if a physical phenomenon could degrade the viewing experience, I would naturally suffer from it, just being unlucky. Not so with the Plus. It's a great little projector. Again, as others have said, no projector is perfect in every aspect, but given the relative merits and drawbacks of them all, you can't go wrong with a Piano for a cinematic DVD viewing experience.
 

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Quote:
I'm using Milori's picture as my windows wallpaper
LOL! Can you actually do that?


If you can animate the desktop like that, plug the computer into your projector and then take a look at it!


(This trick is especially fun for LCD, LCOS and three-chip DLP owners!)
 
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