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Discussion Starter · #1 ·
Although I have never seen a rainbow (don't have a DLP unit yet) I am beginning to see the light.


I think they are due to the Doppler effect as your rapidly moving eyes move from one transitioning pixel mirror to the next. In astronomy, it shows up as "Red Shift". In terrestrial HT DLP viewing, it looks like rainbows.


I also have some theories on the Shroud of Turin and the extinction of dinosaurs, as they may relate to this phenomenon.
 

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Quote:
rapidly moving eyes
If it were due to the astronomical equivalent of red shift (visible spectra doppler), you would have to be moving your eyes fast enough to stretch color wavelengths in order to see rainbows!


You don't have to move your eyes that fast to see these things, so I don't think that it's due to the doppler effect. Good theory, though!
 

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It's simple eye motion making the sequentially presented colors not physically align on the same place on the retina. The displacement of the red, green and blue images is most visible at object edges, particularly bright ones. One might naively expect this to happen only as one changes glance from one portion of the screen to another, but there is more to the story. The effect can be noticed even when the image is still and one attempts to gaze at a fixed point of the screen. The missing factor that most people don't realize is that human eyes don't lock into a fixed position and snap an image like a camera. Your eyes undergo constant, very fine, rapid, saccadic motions even when you look at a fixed point. This shifts the image on the retina about and is actually REQUIRED for our retinas to properly process and encode images for transmission to the brain's visual cortex.


With patient practice it is possible to learn to hold your eyes fixed long enough to experience what happens without saccadic motion. You get few seconds long glimpse of a very interesting effect - objects literally disappear before your eyes. It's tough to do, but it is a powerful demonstration of how the visual system is dependent on saccades to watch the text of a page completely disappear for a few seconds.


The point of all this is that the physical displacement causes the temporally displaced primary color images of a one chip projector to be offset from each other visually thus producing rainbows. Faster color wheels help by reducing the time between colors so eye motion doesn't separate the images as far. Light intensity also affects the temporal resolution of the visual system so playing with the projector luminance can have an effect.


It is unreasonable to expect saccadic velocities and angular deflections to be constant from person to person. Even in the same person, saccadic motions can be altered with a little sedation. If saccadic motion is small, there will be less visible "rainbow." I'm not at all suprised that some people see rainbows all the time while others never see them.




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Guy Kuo
www.ovationsw.com
Ovation Software, the Home of AVIA DVD


 

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The issue of the "saccadic" effect on rainbows has been discussed here before, with inconclusive, uh, conclusions.

I initially vetted the saccadic effect because:

a) It made sense

b) The math works out

c) I'm pretty sure that I first proposed it here. http://www.avsforum.com/ubb/smile.gif (Forgot the medical term though...)


Here is some further discussion: http://www.avsforum.com/ubb/Forum10/HTML/008194.html http://www.avsforum.com/ubb/Forum10/HTML/008297.html


After doing a bit of Google searching on saccades, I came to the conclusion that it's only part of the story- saccades appear to be irregular in nature.

From:
http://www.hallym.ac.kr/~neuro/kns/t...edical/H1.html


I got this (On continuous eye movements):

"...(1) a continuous tremor at a rate of 30 to 80 cycles per second caused by successive contractions of the motor units in the ocular muscles,"...

This tremor is not named, but it is differentiated from saccadic movements, which, again, are irregular. And:"...Also, the brain suppressed the visual image during the saccades so that one is completely unconscious of the movements from point to point..." If we "turn off" visual perception during saccadic episodes, why the rainbows?


The tremor may to be related to both the "rainbows" and the sensitivity some people have to watching monitors wiggle at 60Hz under flourescent lights. Also, the rainbows can be seen on fixed images; it's not a question of video vs. film sources, or even refresh rates.

Jee whiz, folks, we may be onto something cutting-edge in visual perception! If DLP rainbows can easily be used to research visual problems...


What would be nice is if somebody with clinical experience could check this out for us. Of course, there is a marketing possibility here- eyedrops to act as minor muscle tranquilizers:

"DLP-Eyes: Gets the Rainbows Out!"


Only partly joking- note that most of the research is quite recent, and among other things, suppressed saccadic activity appears to be tied to dyslexia.


Should we have an AVS DLP "Rainbow" Poll? Among some questions we could consider:

1) On a scale of 1 to 5, 5 being always, how often do you see rainbows?

2) Are the rainbows triggerable, that is, once you see them, you can't _not_ see them?

3) Do you find yourself forgetting about rainbows for long periods of time? Looking back, did you actually not see them, or did you adapt to ignoring them?

3) Do you see horizontal, vertical or both kinds of rainbows?

4) Estimate your viewing distance and screen size.

5) Do you see flickering computer monitors at 60Hz? Does flourescent lighting make it worse? Does changing refresh rates effect this?

6) Have you ever successfully pointed out the rainbow effect to other viewers, who were not previously aware of them?

7) Have you ever been diagnosed with dyslexia, night blindness, or other organic visual problems?

8) Do you wear glasses or contact lenses?

9) Do you have good peripheral vision? Can you track most action on screen by merely shifting your eyes, or are you always moving your head to follow action?


Please suggest other questions if interested, let's formalize this before springing it on the whole forum.

apg
 

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Quote:
Originally posted by Mr Fixit:
I also have some theories on the Shroud of Turin and the extinction of dinosaurs, as they may relate to this phenomenon.
LOL. Look guys. I think he got you. Hook, Line, and Sinker http://www.avsforum.com/ubb/biggrin.gif




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DVI/HDCP makes your HDTV not ready
 

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Discussion Starter · #6 ·
It's an old ruse that still works. If you want to know the truth about a subject others might not bother to pick up on, just start spouting a little marginally credible BS. It'll drive those who really know crazy until they have set the record straight. Ganks thuys (I think). Fotunately, I'm a dad tyslexic.


Jack
 

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Does anyone else think that this Mr. Fixit is going to be a great addition to this forum?!


What a great sense of humor!
 

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re: "If you want to know the truth about a subject others might not bother to pick up on, just start spouting a little marginally credible BS."


It's a fine art to troll without letting others know you're trolling http://www.avsforum.com/ubb/wink.gif


Fifty quatloos on the newcomer!


We've got a lot to learn from this guy... http://www.avsforum.com/ubb/smile.gif
 

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Uh, may I point out that there are a number of people on this forum who take their work seriously, but often go out of the way to help newcomers along on technical questions. One common trait among newcomer questions is lack of clarity or inappropriate imagery, along with a self-deprecating sense of humor. I, and Mr. Kuo, took the original post seriously; here was a person who was trying to figure out a technical problem, posited a hypothesis, and asked for help.


rgb:

"It's a fine art to troll without letting others know you're trolling."


What a waste of time. Have fun "trolling" folks.

apg

 

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Just thought I would add my 2 cents. I just got my LT150, and I do see rainbows easily. But I commonly have one beer in the evening when watching a movie. Last night, friends were over, so I had 2. After that, I was of course, not drunk, but relaxed. And, rainbows were gone! I really had to try hard to see them. My friends noticed the difference as well. So relax, have a glass of wine or beer, and enjoy!
 

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shahram72 that's the best advice I've heard yet!!!!! http://www.avsforum.com/ubb/biggrin.gif


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Every man is my superior, in that I may learn from him.
MyHTSetup


[This message has been edited by Lou Sytsma (edited 09-20-2001).]
 

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Whoa. I guess I shouldn't have mentioned the "t" word!


Mr. Fixit's initial post wasn't "malicious trolling", but was meant as a humorous discussion starter, IMHO. Doesn't mean the ensuing conversation can't be serious, either.


...Unless someone really thinks there is a resolution to the Rainbow DLP enigma in the Shroud of turin or dinosaur extinction theories...

 

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Discussion Starter · #14 ·
Thanks, all of you, for your responses. Nothing is more flattering, nor more welcoming, than to gain the attention and expertise of some of the best intellects on the forum. Forgive me, apg, for gently pulling your leg. Honestly, my motives were sincere. I assure you, I took your own (and Guy's) thoughtful replies seriously - as appropriate (let me know when you're ready to market the eyedrops). And your suggestion of a controlled study of the rainbow phenomenon has merit. Whether or not this forum would co-operate, I don't know. I'm new here. What I do know is that in this forum I have certainly found a pot of gold.
 

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Thank you for your kind words, Mr. Fixit, although I certainly don't qualify as an "intellect" on this forum, there are others that seriously do qualify. On such subjects as saccadic effects, I'm strictly a dilletante; my fields of expertise would bore most of you to tears.


In the book "Cannery Row", the character Doc always assumed that questions asked were from people who seriously wanted to know the answer; there were no stupid questions, only stupid answers. The character Hazel always asked Doc questions, often the same questions over and over. Doc always answered, not realizing that Hazel was just trying to keep the conversation going. Hazel was "trolling", in a way, but not maliciously.

When I used to teach at the local community college, I found that there was a certain percentage of students who really wanted to learn, but sadly, the majority were just biding their time. I also learned something- nobody can teach. This is an impossibility, outside of boot camp. All that one can do is create an environment where learning is as easy and interesting as possible.

There is a lot to be learned on this forum- the signal to noise ratio is extremely high, and the jerk contingent is vanishingly low. I apologise for assuming that you were a "troll" in my last post, and I hope that we have all learned a few new things.

apg

 

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Mr. Fixit and esteemed forum members,

Since it appears that I was the one to "cast the first stone" and label Mr. Fixit's original post as a tongue-in-cheek at best (although I didn't call him a troll!), I do apologize.


I'm usually a critic of those who cast aside newbie questions and scold them for not doing a search. It's just that the theory immediately reminded me of an explanation by Cliff Clavin (of the show Cheers) about how the sound you hear from knuckle-cracking is actually the joint motion breaking the sound barrier. Apparently, what you hear is actually a "miniature sonic boom".


OK. So please? Can I still play ball with you guys?


Hey, I just noticed I've made it to 100 posts! Good thing that counter doesn't count just the "intelligent" posts. http://www.avsforum.com/ubb/biggrin.gif

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DVI/HDCP makes your HDTV not ready


[This message has been edited by jhill32 (edited 09-21-2001).]
 
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