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I scanned in a picture of the Archimedes color wheel from Infocomm (I honestly can't believe how much time I spend in this forum!)


Here is what it looks like:
http://www.dilard.com/dilard/images/...archimedes.jpg


As long as I have it, here is a picture of the "light tunnel" that feeds the wheel. I'm not sure how the "recycler" part of it works.

http://www.dilard.com/dilard/images/htpix/dlptunnel.jpg


Hopefully, this new wheel will cure the rainbow problem in the single-chip DLP projectors.


(EDIT: The original image URL was incorrect)


[This message has been edited by milori (edited 06-16-2001).]
 

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I notice they couldn't resist putting a white section on the wheel between blue and green http://www.avsforum.com/ubb/smile.gif As for the "recycling" and "using all the light", well, that seems more like hype than anything else. It just doesn't compute...


Mark, thanks so much for all your reporting on Infocomm. I'm in the market for a new projector and your reports and other comments on this forum have been quite helpful. Leaning toward the PLV-60.


Frank L
 

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Milori,


Thanks for the scans!! I think I have this figured out now. So nobody post anything to confuse me again.


At one point in time, white light hits the color wheel, then only one component of RGB is let through, the other two colors get reflected back into the tunnel and by the time those components come back to hit the color wheel a new filter is present. The total reflection time for recycling has to be incredibly short cause we are dealing with the speed of light here. d'oh!


The spiral pattern is the key to getting this rapid change in the rgb filter color, otherwise they would have to spin the wheel so fast the bearings would melt! They are recapturing 2 out of 3 components of light intensity that are normally thrown out in a DLP projector using the standard three segment color wheel.


This diagram also shows scrolling color on the DMD chip, that is the DMD chip is "seeing" all three colors at the same time. I still haven't figured out how all of this is sync'ed so that each pixel on the DMD chip knows exactly what color it is seeing.


Also I would think that the frequency in which they cycle through the colors exceeds that of even a RGBRGB color wheel so say a permanent goodbye to the "rainbow effect" everyone is so sensitive to on current single chip DLPs.


Ok, so I'd like to place an order for a $5000 SCR color wheel, .8" HD1 ( 1280 x 720 w/ DM3) DMD chip based projector for my home theater, by 2003 please.


Ricardo



[This message has been edited by RicardoD (edited 06-17-2001).]
 

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I asked the Infocus 530 product manager at the Infocus booth about this new "archimedes" wheel. He said that he did not think it would help the HT situation or the "rainbow" issue but was more for business applications. The main purpose is to have a brighter light he said.


I was somewhat surprised by this since I thought it would break up the patterns that typically are involved in the perception of a rainbow.


Time will tell.

 

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Ricardo,


You've almost got it, however it doesn't just reflect the light and put the next filter there before the light hits it again (it's just not possible! Speed of light == 3.0*10^8 metres/sec).


Remember dichroic filters pass one colour and *reflect* the rest of the light (as oppossed to a regular filter that passes one colour and absorbs the others). All three colours of dicroic filter are illuminated by light at one time, the light reflected back by the dichroic filters bounces back from the "recapture light tunnel" and goes through a different colour of dichroic filter. Look closer at the diagram and it'll make more sense.


rlsmith,


I gotta agree with the Infocus product manager, the primary purpose is to increase brightness. Of course, we need that just as much as business users! I don't think that the pattern would significantly reduce the rainbow effect, you're still cycling colours over time. However, TI's new HT chips should address those issues. Those new HT chips should also support the SCR wheel...


Regards,


Kam Fung
 

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Seems like two threads are going on about nearly the same thing.


While this new wheel may not have been done to cure the rainbow effect, it may be inherinet in its design.


Does anyone know, from seeing the design, if the colours scroll 2 times faster? From what I can see, it would have scrolled all three colours once, by half a spin of the circle. I say this because there are two sets of colour spirals, and one starts just as the other matching colour is reaching the top. This would therefore make it equivalent to a 2x, or RGB RGB colour wheel.

Agree?


I must admit that I am absolutely amazed at how they plan to get the timing done right with this system. As others have said, this is quite a feat, for the different sections of the DMD have different colours being shone on them, and this changes constantly, at least one complete cycle through one revolution of the wheel.

What processing must be involved!!! and if there is any imprecision, boy, what a catastrophe it would be if the timing was off by just a bit!!


Maybe that is why the white segment is there, so it can be used as a synch on some of the older colour wheel systems.


Mind you, I am hoping this works as addvertised...



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David Mendicino

Sharp xv-s55u (Don't laugh) http://www.avsforum.com/ubb/smile.gif


[This message has been edited by David Mendicino (edited 06-17-2001).]
 

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I think that the point of the archimdes spiral is not to make it faster, but to provide multiple simultaneous exit points for the different colors of light.


If for example, red hits a blue segment, it gets bounced back and has a 1/3 probability of hitting a red segment red on the second bounce if it is randomized. Without the spiral, it would hit blue again. There is loss on each bounce so multiple bounces are attenuated, but it is a clever way of improving throughput.


If one depended on the speed of light, they would need a cavity with very high Q.


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Ken Elliott
 

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Yes, that is correct.


However, this sytem also "scrolls" the colours across the DMD. In that sense, in one half spin of the wheel, all three colours have been scrolled across the DMD completely, once. There are two spirals on the wheel. In a complete cycle, RGB will be completely scrolled across the DMD twice, making it perform very similar to the RGBRGB 2x colour wheel. However, this scrolling may lead to a new artifact alltogether http://www.avsforum.com/ubb/redface.gif


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David Mendicino

Sharp xv-s55u (Don't laugh) :)
 

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Clever design. It's suprising that the reflected light doesn't defocus the image when it bounces back. Those tunnels must be high precision designs.


It looks like the distinct pattern on the outer and inner edges of the wheel that's not part of the archimedes pattern would be used to synchronize the electronics so there's no chance of error.


- Chi

 

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Kfung, David


Thanks for makes things a bit clearer for me and not adding to the confusion. Seems that all that is left is the clever way this is all synced with the DMD chip.


Ricardo
 

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This Archimedes wheel looks like an electromechanical implementation of the French SECAM OTA analog television system, also adopted by Eastern bloc nations in the early days of TV.


Look at a SECAM transmission on a color French TV set and you'll see why Sequential Color systems still end up looking like you're watching through a cheap prism...

Human eyes want to see all the color *at the same time* (unless someone devises quantum-time-shifting versions of dichroic filters http://www.avsforum.com/ubb/wink.gif )


"Give me a lever long enough and a place to stand and I will move the earth."

ARCHIMEDES, circa 240 BC


"Give me a colour wheel big enough and spinning fast enough and I shall eliminate rainbow artifacts"

INFOCUS, et al 2001 AD



More cool Archimedes info: http://www.mcs.drexel.edu/~crorres/A.../contents.html


[This message has been edited by Rgb (edited 06-18-2001).]
 

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If SECAM works the way I think it does (and the way the name translates), that is sequentially showing each colour for each field, then it would more correctly be compared to a rather poor colour wheel. At higher frequencies (4x 60Hz for example) our eyes should no longer be able to perceive the flicker and spatial separation of component colours should be far less objectionable. It's really a matter of getting the colours cycling at a high enough rate. After all, DLP chips are really just pulse-width-modulators (PWM) and the switch light "on" and "off" very rapidly, that's not so different from the lower order effect of the colour wheel. It's just a matter of speed.


The human eye doesn't need to see colour all the time, it's actually quite adept at summing responses over time and integrating them into a complete image.


Regards,


Kam Fung
 

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Hi,


SECAM doesn't work the way you think.


Coulour information is effectively sequentially transmitted on two FM carriers but a 64µS delay line permit to re-arrange that stuff and to get simultaneously all the colours on the screen.


The main improvment of SECAM on NTSC is to eradicate the phase shift of NTSC carriers (PAL does it also in a different way).


On the other hand, the color definition is divided by two (at any time you transmit only 1 colour information and

not 2 like in NTSC)


My 2 cents.



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Serge Lacroix - Cherbourg - France
 

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KFung,


You are correct about the speed of light thing; however, the rep at the Unaxis booth told us that the delay going up and down the tube was what caused the increase in brightness. I quickly told him we were talking about nanoseconds and still contended that the colored light kept bouncing back and forth until the wheel rotated enough to let it pass. Oh well.


The situation that you describe where it actually bounces back and forth until it reaches a segment that it can go through is more acurate; however, it will have a strange angle when it finally goes through which to me would indicate that the scrolling color bars might have some wash out to them (i.e. less purity in the primary colors).


Overall I think it is a promissing technology but I don't think it will be utilized well for at least a year.


Other tidbits:


Has anyone seen the white paper for this from TI? I couldn't find it eventhough they said in a press release that it was available.


All of the colorwheel manufacturers were displaying colorwheel's with either a small clear section or no clear section at all. This is a good sign in my opinion.


Unaxis is headquartered in Lechtenstein which is tiny country between France and Germany if I remeber correctly. I think their population is in the thousands and most of those work selling duty free merchandise in thrift shops.


-Mr. Wigggles


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The Mothership is now boarding.
 

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Kinda reminds me of the time when the Canadian governement was after me for non-payment of student loans. They sent a collection agency after me to collect their funds. I was quick to notice (according to the supplied paperwork) that the collection agency headquarters was located in the Barbados... to avoid having to pay the canadian government taxes of any kind...


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goosystems.com


Ken Hotte

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Iceman,


I don't think I said poor slobs.


-Mr. Wigggles


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I don't know about the light reflecting over and over. At 80% (just a guess) reflectivity, 5 bounces and you're down to 33% of the light you started with.


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Noah
 
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