[tim_f]

I just want to say Hi to all of you. This is a great forum.

Just joined the forum. Been reading for months now and really enjoy the reviews, the comments, the fun, ext, and ext.


But moving on.


For a new guy it's a long posting.


I've been looking into getting either a LT150 (DLP) or VT540 (LCD) for my home theater. I've read great reviews on both.


I understand the screen door effect with the LCD's (don't know if I can live with it though). I've seen the effect from some of your pics you have been posting. But could not find any on the rainbow effect (which would be hard to capture). Also reading some of your post, and it seems know one knows really why these effect happens to some people and not others, why some projectors show more than others, and why hooking them up to HTPC, SD, or Progress DVD show the rainbow effect.


I wanted to under stand why this happens too. I'm one of those who will dig deep to find the answer. So I've been doing some research on the Internet. After searching, I have found some answers to some of the reason why this happens.


These theories are based on what I read and my own conclusions form reading these articles.


One place I found is from ExtremeTech, the article is on Flat Panel Technology but they explain about DLP's. (ExtremeTech article click here)


Short Summery of the article:

DLP use a technique called Field Sequential Illumination. As you know they use for the lower price projectors a color wheel (red, green, blue, and sometimes white to add more light to white and lighter shades of colors in the image). All this happens faster than the human eye can see, and the separate fields are combined in the brain where they are perceived as a single, full-color image. (Since this is done in the brain that is probably why some of you are more prone to it than others.)


Also field-sequential images can appear to break up into different colors if you look from one spot on the screen to another, especially if the image has small white objects on a black background. In projector applications, the motor used to spin the color wheel can be a noisy distraction (vibrations or unbalanced). Which will cause the rainbow effect. (Which some of you agree with that it could be the color wheel.)


Now that explains one reason. The other is on technology. Talking to an engineer explained why your PC, CABLE BOX, or DVD sometimes shows the rainbow effect.

It is do to the A/D Converter (Analog to Digital Converter), which is in the projector. He believes that it might not be a good one or fast enough for the conversion. That is why using Svideo (analog input) does not do well. The reason PC's work great, is that's it uses Digital to Digital no conversion going on, unless your video card is not the latest or greatest technology. And also goes for the same reason that some Progressive Scan DVD players, which are digital to digital, sometime show the rainbow effect. Some technology is better than others.


I hope this helps anyone with the rainbow effect questions on why this happens.


One more thing. Check this article also by ExtremeTech on Color Depth. Which will answer other questions on CRT vs. LCD, and on colors on LCD projectors (this also proteins to DLP since they are based on the same principles) and blacks (for those obsess with blacker than black). (Click here for Color Depth and scroll down to Color Depth.)


For those like DLP here is a neet sight to look at.
www.dlp.com


Note:

These theories are based on what I read and my own conclusions form reading these articles. (I'm new to this site so please take it easy on me if you have any arguments on this matter. Thanks.)

 

[ferrocene]

Just some minor corrections and a comment.


I think most people realize how the rainbows are created. The rainbow effect is the same as staring at a ceiling fan. If you move your eyes quick enough on a fast rotating fan, you can see the individual blades of the fan. Your eyeball doesn't move in a smooth line, it stutters back and forth.


The same thing happens with a 1 chip DLP. If you scan your eyes from left to right really quickly, you see the "single fan blade" of primary colors. The illusion of the blurry circle on your ceiling breaks down into individual blades with the right eye movement. Same with "seing" the color wheel.


How do you make it go away? Well, don't watch action movies with white/black contrasts. http://www.avsforum.com/ubb/smile.gif I'm staring at my ceiling fan now, waiting for an epiphany.


I believe milori's dlp rainbow generator would be more effective if the screen was solid black. In the middle there is a fat vertical white bar. Then randomly pop up an image or shape on the left side of the screen. Then randomly soon after make an image pop up on the right side, and repeat. This would cause your eyes to quickly track the flash of an image, from right to left, and in the process you would peripherally see the individual colors surrounding the white bar.


nit: "The reason PC's work great, is that's it uses Digital to Digital no conversion going on, unless your video card is not the latest or greatest technology. And also goes for the same reason that some Progressive Scan DVD players, which are digital to digital, sometime show the rainbow effect."


Not a single consumer DVD player AFAIK outputs a digital signal (perfect bit copy, anyone? copy protection?) Some projectors accept a digital signal, but not many. The LT150 does not. You can use these for a HTLapTop. Digital to digital would be nice eliminating a lot of calibration.


-Erik-

 

[tim_f]

ferrocene I like your simple explanation. I would of use a strop light effect with my hand. But yours is good enough.


Yes you are right about the PC's and Progressive scan DVD signal. It was late and was not thing straight here is a better explanation:


PC's us a VGA connector that have three separate lines one red, green, and blue color signals, and two lines for horizontal and vertical sync signals. So the projector have to do less conversion on the signals. Where in Svideo all these signals are combined in a single signal, and the projector has to do the conversion. So take that in to fact that your PC video card has a better Digital to Analog converter than the projector. Or your Progressive scan DVD player. Also for PC they use Pixels like your monitor which also the projectors uses, so the conversion is a lot easier.



I hope that was a little better explanation than before.