[sparky]

Hi Simon,


Good to have someone else from the UK on the forum, I know there are a few others as well.


Yes the rainbow effect is what you are seeing when you blink. its mainly noticeable with fast moving white on a dark back ground.


The colour wheel is a disc made up of red, green, blue and white sections that rotates in front of the lamp. the micro mirrors then reflect the relevent colours to make up the image we see.


Cant help with links, but try a search.


When you get the chance try an Iscan or HTPC to improve the image. You can e.mail me if you like.


Sparky.

 

[David Mendicino]

Ok, before you get told to do a search, I will try to help you here:


The DLP you own is a single chip DLP. That means to produce an image, which LCD and DILA do using three panels, the DLP must use one chip, and flash the colours on it at separate times, instead of making one image from the combination of three panels. To accomplish this, singlechip DLP uses a colour wheel, which flashes the colours on the chip one after another. The chip is sync'd with the wheel, so the mirrors are in the correct position when they get their dose of colour. Some colour wheels may use a clear section to boast the light output.


This is what the colour wheel does. The rainbow effect you see is what can simply be called an imprint on your eyes of the flashing of the colour wheel.


A new thing that is going on is to speed up the colour wheel, either by making it faster or adding more segments of colour, to the point where it is changing the colours faster than your eye differentiate and imprint.

Think of a strobe light. The faster it strobes, the less you can tell the difference between it being on and off. This is how film works, by flashing images faster than the eye can tell.


Hopefully, this was usefull, from all the knowledge I have aquired at my time here in the forum.


(ps. Sparky beat me to it while I was typing... http://www.avsforum.com/ubb/frown.gif


------------------

David Mendicino

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


[This message has been edited by David Mendicino (edited 04-24-2001).]

 

[simon]

hi all,


after a bit of digging, am i right in thinking that the rainbow effect is what i see when i blink when watching a movie on my infocus 420?

i don't see it all the time only with some material.


what is the colour wheel and what does it do?


if you could point out some links on the forum i shall go read.

thanks,


simon

 

[sparky]

David,


Better explanation, thankyou.

Sorry for being so fast, but I thought I would support the UK residents of the forum.


Sparky

 

[David Mendicino]

Yes, that's because the colour wheel is synch'ed to the frequency of the signal. So, if you have 72hz signal, the wheel spins faster than 60hz, and even less rainbow!




------------------

David Mendicino

Sharp xv-s55u (Don't laugh)

 

[simon]

thanks guys,


just got a dvd drive for the pc so will try that over the weekend.


it seems not be as noticeable when using 60hz signals.


simon.

 

[sparky]

David,


Are you saying that the higher the input frequency the faster the colour wheel goes?

If so why dont we all use HTPC and set up custom resolutions and frequencies 80 / 90Hz to eliminate this problem. Might be worth a try.


Sparky

 

[DanHouck]

Good idea Sparky, but I think there's a physical limit to how fast the current generation of single RGB wheels can turn. Plus, I recall reading on another thread that they get louder as they spin faster.


The soon to be released 6 segment RGBRGB color wheels will by definition double the speed at the same 60 to 72 hz sync speed. It will be interesting to see if this is sufficient to eliminate the rainbow artifact for the sensitive, like me unfortunately. Since the color change speed is going to double, will other kinds of artifacts be introduced? Hope not!


If not, that will ice it and I'll go for the new generation of higher contrast, higher output LCD.


BTW, David that was one of the best explanations I've seen of how the DLP/color wheel works. Clearly your addiction to this forum has had some benefit!


Dan

 

[David Mendicino]

Thanks Dan.


I will admit though, that my knowledge of DLP comes from becoming obsessed with the flaw of DLP. Why? Because I want it!!! I have seen LCD, and own one, and must admit, while in same cases the differences are smaller, DLP usually has better blacks, and no screen door effect. (Plus, as a side note, because the DLP response time is so high, it is MUCH better for videogames than LCD. WHen I play games on my LCD, any really fast moving object gets blurry.)

However, like you, I am VERY sensitive, or "aware" of the rainbow artificat. Even on the newest seleco HT200 I see it. I have read, and am sure, that those new LCD's are great, probably magnitudes better than my measly Sharp. That is why I follow the colour wheel, to find out if they actually change it. My hopes were dashed with the Seleco. I have new hope, but am at the same time optomistic, for the new 6 segment colour wheel. And, it is not just for me, but for all who watch it. I WOULD be displeased if I didn't see the rainbow but other audience members did. It would be a mochery of my system.



Your response was correct re: frequencies. The colour wheel does have an upper limit, I am sure, and the projector, if I remember correctly, downconverts this. It must, because if the wheel is not going as fast as the signal, than it will misalligned in terms of the colours on screen.


Just my opinion,



------------------

David Mendicino

Sharp xv-s55u (Don't laugh)

 

[DanHouck]

Yeah, David, my sentiments exactly. I'd really rather have a DLP though I confess I'm tempted sorely by the new generation of LCD. But there's just no getting around that lack of fill, particularly if you want a 100" diagonal picture and you want to sit 12' away from it. On the other hand, the rainbow artifact on the generation of DLP shown at CES just didn't cut it for me. I have this $100K eyeball that is ultra rainbow sensitive.


Bummer!


If the 6 section wheel plus better software doesn't cure it, I' m afraid it's LCD for me!


Dan