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Discussion Starter · #1 ·
If you are shopping for a DLP and would like to compare "relative rainbows", here is a new tool for seeing them. It's a tiny (28 KB) program that draws a test pattern that is purposely cruel to a DLP projector...

DLP Rainbow Test


If you haven't seen rainbows before, I have a feeling that you will see them with this tool.
 

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Cute little program Mark, thanks :)


I was pleased to see that my newly thumperized Davis DL450 withstood the torture fairly well. The bouncing colored balls look just fine (no rainbow), but I do see a slight rainbow at the leading edge of the scrolling text (at the top when moving up and at the bottom when moving down). This is consistent with my experience that I only see rainbows with this projector during the scrolling credits at the end of some movies (specifically, fast scrolling white text on a black background).


Actually the worst rainbow I ever see is with the windows white pointer cursor. I have a track ball and so can move the cursor very rapidly back and forth on the screen. I always see rainbows when I do this (or more accurately I see multiple pointers simultaneously...some red, some green, some blue, and some white), but the cursor has to be moving REALLY fast...much faster even than the text in your program.


Thanks again for the demo program, It is a useful tool for people comparing the rainbow-free-ness of different DLPs.




[This message has been edited by Jim Tittle (edited 08-18-2001).]
 

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Hey Mark NO FAIR !!! http://www.avsforum.com/ubb/biggrin.gif !!


That's just plain cruel you will teach a multitude 'how' to see them and generally lower the value of DLP's everywhere (or are you just trying to pick some newly cheap bargains you sneaky dog you http://www.avsforum.com/ubb/wink.gif )... Ahhh I get it, you want to upgrade to a G15 and thought you would again prop up DILA prices in time for resale !!


Seriously though (and I know many will cry disbelief) I have no problem on my (non Thumperized) DL450 (Viewsonic) clone via HTPC at 72hz to a DIY blackout material screen.. If you want to make it worse allow a 2x speed option to make the text faster I think this will get it there.. I think it is fine now due to a few factors. First the screen does not have the gain that many other are using and so I think this saves me a bit (at the expense of light of course) plus the 72hz HTPC setup is far better (for me) than my original 60hz... When I can get commonly viewable rainbows with this app I will attempt to find out if 85hz (the max of the PJ I think) is again better for rainbow and if this introduces any / more stuttering to panning shots...


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HTPC without using windows... GUI Front Ends for Home Theater
 

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Well let me start by saying I am not prone to the rainbow effect..Maybe that is why I don't spend countless hours looking for flaws.


It is kind of like a spouse(they ALL have flaws,if it bothers you get another one).


It is relative to your environment how "bad" it will look.

(ie screen gain,distance to screen,input,etc...)


I will add it would look ALOT worse looking at the VISA bill and seeing the RETAIL price on my statement.


The projector was a TREMENDOUS bargain at the dell price.


I think we could pick apart any projector if we spent all day and night looking for flaws,however if you are consumed by this you really have too much time on your hands!!!


KD
 

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Strange..


I am sensitive to the rainbow effect, especially when I try. On my LT150 I can see the rainbow most prominently during dark scenes with a bright moving object.


Using the DLP rainbow test does not help me see the rainbow at all. Can I please have a refund? Ok, can I at least be compensated for the download time? :)


I wonder just how personal the effect is. I think removing the background crosshatch would cause me to see the effect in the demo.


jeff
 

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Can someone explain why and how some people claim to not to be able to see the "rainbow effect" and others see it constantly? I can easily see this effect occur during virtually any portion of video from all kinds of DLP projectors (Seleco, NEC, InFocus, etc..). Is it truly that some people's eyes are sensitive to it? If that's the case, I feel bad for folks like myself, because it detracts from an otherwise enjoyable viewing experience. http://www.avsforum.com/ubb/frown.gif




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DMan
The Academy Home Theater
 

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Discussion Starter · #9 ·
Sorry, guys. The test wasn't meant to be offensive or to put down any projectors.


I've just been spending a LOT of time with the LT150 the past few days, and have been seeing a LOT of rainbows.


Late last night (check the time), I had this crazy idea to see if I could nail down the cause...and possibly find a solution. No harm meant. In fact, it appears that the program doesn't even fulfill it's first goal...to show the issue.


By the way, for those of you who can't get the program to "work" try following one of the moving objects as it travels throughout the screen. If you can follow Blue without problem, try Red. If you can follow Red without problem, try Green.
 

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Quote:
Originally posted by DMan:
Can someone explain why and how some people claim to not to be able to see the "rainbow effect" and others see it constantly? I can easily see this effect occur during virtually any portion of video from all kinds of DLP projectors (Seleco, NEC, InFocus, etc..). Is it truly that some people's eyes are sensitive to it? If that's the case, I feel bad for folks like myself, because it detracts from an otherwise enjoyable viewing experience. http://www.avsforum.com/ubb/frown.gif

I think it has to do with the operation of each person's eye and brain. I read a book by HP on computer color that provides an introduction to the vision system. Near the center of the field of view the eye can see color and that there are separate cones (or is it rod's I don't have the book with me) that are sensitive to Red, Green and Blue light. They actually have a light frequency sensitivity that peaks in the red region, etc. Each of these cones has nerves that send out a train of electrical pulses that is proportional to the (red wavelength filtered) light luminance striking them. These pulses go to the brain and also to color difference cells (?) that put out a pulse train proportional to color differences (e.g. yellow minus blue, etc.) This pulse train also goes to the brain.


Also each persons eye does a color averaging with time and that is how we can see (in a DLP showing a static white screen for example) white when actually the DLP is pulsing Red Green and Blue flashes to make white. This averaging is a function of the rate of the color change and the color wavelength. Thus if the color wheel were moving slow at say 10 revolutions per second each person would see a red flash a green flash and a blue flash for static white screen. If the wheel speed is increased to 100 revolutions per second then everyone would see white (not see the individual colors).


MY OPINION is that the rainbow effect has to do with the strobing effect of the RGBW color wheel and the pulse train rate produced by the nerves. Apparently each person has slightly difference threshold of sensitivity to rate of change of color. Perhaps the 60 HZ rate for some (like yourself) is ok for color averaging for non moving color fields (e.g. solid white), but is not fast enough for spatially moving color fields like a movie. Thus some see the rainbow and some don't. I for one never see a rainbow. I guess I am lucky http://www.avsforum.com/ubb/smile.gif




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Gary


STOP DVI/HDCP!

DVI/HDCP! ~= HD-DIVX!!!

DO NOT SUPPORT JVC or anyone else who supports this!
 

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Hey, Mark, no rainbows on my Boxlight 38T. No global warming either! http://www.avsforum.com/ubb/biggrin.gif


Seriously, this is a great idea you've got here. If you have a "rainbow test pattern" you can run while tweaking, it should make it a lot easier to try things out and see the results in a reproducible manner.


Dan
 

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ok totally unfamiliar with Digital PJ's here.. but can the Lt150 or other DLP for that matter sync to something like 96Hz or 120Hz for that matter??


would that eliminate or at least dminish the rainbow effect?


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Buyer's Guide to HTPC for Newbiess>c>
 

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Discussion Starter · #14 ·
Since I've been standing in the middle of my theater room while the LT150 is on holding a (shiny metal) tripod mount and a notepad, not only have I been seeing rainbows...


I HAVE RAINBOWS ALL OVER ME!


Seriously, I think that they are much worse when you have reflecting metals surfacing and *actual* moving objects (pens, notebooks, laptops, tripods, etc) and not just moving objects in the image.


I find that I hardly see them in movies now that I've been immersed in them.


Try waving a notebook and pen around in the image path for some real colorful images.


I know, I know...this isn't "normal" behavior. Light me on fire for not sitting still and watching the darn movie!
 

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Quote:
Originally posted by milori:



I HAVE RAINBOWS ALL OVER ME!

Milori, you have to get out more!!!



Mike


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Let's go out to the lobby.

To have ourselves a snack!

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There is also a situation called an after image that may be coming into play. If you stare at a solid colored object for a while (~20 sec) then look away at a white area you will see the same shaped solid object as before (in the white area) but with a pale shade of the complement of the first color. This is given as an example in the HP Book.


Color vision (how our eyes actually work, etc.) is an interesting subject, and I wish I had more time to put into it.




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Gary


STOP DVI/HDCP!

DVI/HDCP! ~= HD-DIVX!!!

DO NOT SUPPORT JVC or anyone else who supports this!
 

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Just a quick note on rainbows, and the LT150 in particular...

The human eye "strobes", that is, it vibrates back and forth, at around 200(?) hz. When test subjects had their eyes sedated, all they could see was a gray blur, _but_ while they moved their heads, vision returned. The cones apparently saturate when fixed with a steady source of fixed-wavelength light, so the strobing acts to clear them.

(This was from a Scientific American article from maybe 20 years back- I can easily be fuzzy on the details...)

When I feed a high contrast JPEG slide to the LT150, from either a computer (xga 75 hz.) or from the CF card, and jerk my head back and forth, I see rainbows. The image doesn't have to move, just my eyes. We did this test last Friday night, and four out of nine hot tub dwellers saw the effect.

My guess is that there is an interaction between the natural strobing of the eye, and the speed of the colorwheel. Some people are sensitive to it, as some people are sensitive to monitors "throbbing" under flourescent lights. And some are not. Changing refresh rates may help, as well as limiting extreme contrast ratios.

I see them, but they don't bother me. After the tests, we watched "Nightmare Before Christmas", and as in not thinking about elephants, after a while, not thinking about rainbows caused them to minimize.

Now, twenty years ago, there was a part of our population that would have said "I see rainbows! Groovy! Pass the pipe..." That was then...

apg
 

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Quote:
Originally posted by Jim Tittle:



Actually the worst rainbow I ever see is with the windows white pointer cursor. I have a track ball and so can move the cursor very rapidly back and forth on the screen. I always see rainbows when I do this (or more accurately I see multiple pointers simultaneously...some red, some green, some blue, and some white), but the cursor has to be moving REALLY fast...much faster even than the text in your program.

I was able to display rainbow "on demand" by using a similar method. In my case I used a laptop and by merely moving the white arrow pointer (slow or fast) over WinDVD's dark idle screen I was able to see rainbow all over the pointer. The background needs to be dark using the default white pointer. This was using a NEC LT-84 projector, can other try this and report ?


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Sergio R.
 

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I am on mine now, as I type this....a slithgt jitter in the picture i never notcied before is irking me i have to find out what it is.


Aside from that I have yet to see nay rainbows. I see them if i look towards the lens, but not on the screen even with milori's test. I dont know, it may have something to do with this bluw wall I am projecting on?



Chris
 
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