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Discussion in 'Televisions' started by lee31, Jan 6, 2005.

  1. lee31


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    DLP's strengths are two fold. The most obvious is contrast ratio, which in better machines can triple the best LCD can offer, giving a more television like picture. The second is pixellation. On higher resolution DLP machines the pixel structure becomes virtually impossible to see (a result of not being as perfectly focused as LCD which is an advantage for video viewing).

    The weakness is the "rainbow effect" which is the common term for the colour seperation that can occur because DLP projectors rely on a spinning colour wheel made up of red, green and blue (and sometimes clear) filters. Because each colour is in effect being displayed seperately, some people can detect this seperation.

    The Advantages of DLP Technology

    There are several unique benefits that are derived from DLP technology. One of the most obvious is small package size, a feature most relevant in the mobile presentation market. Since the DLP light engine consists of a single chip rather than three LCD panels, DLP projectors tend to be more compact. All of the current 3-pound miniprojectors on the market are DLPs. Most LCD projectors are five pounds and up.

    Another DLP advantage is that it can produce higher contrast video with deeper black levels than you normally get on an LCD projector. DLP has ardent followers in the home theater world primarily due to this key advantage.

    While both technologies have seen improvements in contrast in the past two years, DLP projectors still have a commanding lead over LCDs in this regard. Leading-edge LCD projectors like the Sony VPL-VW12HT is rated at 1000:1 contrast, and Sanyo's PLV-70 is rated at 900:1. Meanwhile, the latest DLP products geared toward home theater like NEC's HT1000 are rated as high as 3000:1. Less than two years ago the highest contrast ratings we had from DLP were in the range of 1200:1.

    This boost in contrast is derived from Texas Instrument's newer DLP chip designs, which increase the tilt of the mirrors from 10 degrees to 12 degreees, and features a black substrate under the mirrors. These changes produced a significant advance in contrast performance that simply did not exist before.

    A third competitive advantage of DLP over LCD is reduced pixelation. These days it is most relevant in the low priced, low resolution SVGA class of products. In SVGA resolution, DLP projectors have a muted pixel structure when viewed from a typical viewing distance. Conversely, most SVGA-resolution LCD projectors tend to have a more visible pixel grid. This is entirely irrelevant if you are using the projector for PowerPoint slide presentations. However, it is more problematic for a smooth video presentation. For this reason, we don't normally recommend SVGA-resolution LCD projectors for home theater. Conversely, the revolutionary InFocus X1 is a DLP-based SVGA resolution projector. It is selling now for under $1,000 and is an incredible deal for the home theater enthusiast on a limited budget.

    In XGA and higher resolution, DLP technology pretty much eliminates pixel visibility from a normal viewing distance. However, the latest WXGA resolution LCDs do so as well. So with higher resolutions, differences in pixelation are not the big competitive battleground they used to be. DLP continues to hold a small competitive edge, but the dramatic advantage of DLP over LCD no longer exists. The screendoor effect is receding into history as a problem of days gone by.

    A Potential Problem with DLP: The Rainbow Effect

    If there is one single issue that people point to as a weakness in DLP, it is that the use of a spinning color wheel to modulate the image has the potential to produce a unique visible artifact on the screen that folks refer to as the "rainbow effect," which is simply colors separating out in distinct red, green, and blue. Basically, at any given instant in time, the image on the screen is either red, or green, or blue, and the technology relies upon your eyes not being able to detect the rapid changes from one to the other. Unfortunately some people can. Not only can some folks see the colors break out, but the rapid sequencing of color is thought to be the culprit in reported cases of eye strain and headaches. Since LCD projectors always deliver a constant red, green, and blue image simultaneously, viewers of LCD projectors do not report these problems.

    How big of a deal is this? Well, it is different for different people. For some who can see the rainbow effect, it is so distracting that it renders the picture literally unwatchable. Others report being able to see the rainbow artifacts on occasion, but find that they are not particularly annoying and do not inhibit the enjoyment of the viewing experience. Fortunately, the majority of the population either cannot detect the rainbow artifacts, or if they can they are not overly bothered by them. The fact is if everyone could see rainbows on DLP projectors the technology never would have survived to begin with, much less been embraced by so many as a great technology for home theater video systems. Nevertheless, it can be a serious problem for some viewers.

    Texas Instruments and the vendors who build projectors using DLP technology have made strides in addressing this problem. The first generation DLP projectors incorporated a color wheel that rotated sixty times per second, which can be designated as 60Hz, or 3600 RPM. So with one red, green, and blue panel in the wheel, updates on each color happened 60 times per second. This baseline 60Hz rotation speed in the first generation products is also known as a "1x" rotation speed.

    Upon release of the first generation machines, it became apparent that quite a few people were seeing rainbow artifacts. So in the second generation DLP products the color wheel rotation speed was doubled to 2x, or 120Hz, or 7200 RPM. The doubling of the refresh rate reduced the margin of error, and so reduced or eliminated the visibility of rainbows for many people.

    Today, many DLP projectors being built for the home theater market incorporate a six-segment color wheel which has two sequences of red, green, and blue. This wheel still spins at 120Hz or 7200 RPM, but because the red, green, and blue is refreshed twice in every rotation rather than once, the industry refers to this as a 4x rotation speed. This further doubling of the refresh rate has again reduced the number of people who can detect them. Nevertheless it remains a problem for a number of viewers even today.

    How big of a problem is the rainbow issue for you?

    If you've seen earlier generation DLP machines and detected no rainbow artifacts, you won't see them on the newer machines either. The majority of people can't see them at all on any of the current machines. However there is no way for you to know if you or another regular viewer in your household are among those that may be bothered either by visibly distracting rainbows, or possibly eyestrain and headaches, without sitting down and viewing a DLP projector for a while.

    Therefore, if you think you've identified a DLP projector that is just right for your needs but you are not sure whether this will be a problem, there is an easy solution. Find an alternative product that is either LCD- or LCOS-based that would be your second choice if you find that DLP won't work for you. Then find a customer-service oriented dealer who sells both models, and who will allow you to switch the DLP product for the alternative after testing it out for a few days. There are a number of service-oriented Internet dealers who will be happy to make such arrangements, and there are plenty who will not. But if you choose a dealer who is more interested in your satisfaction than in closing a quick deal (and they are definitely out there), you will end up with a thoroughly satisfying solution in the end.
  2. mort

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    Sep 5, 2002
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    cheers for that lee :smashin: it confirms what i already thought... if your thinking of getting a dlp set you have to see them yourself.
    everytime ive seen the tosh ive never experienced the rainbows so hopefully im immune :) to em
    to be honest ive been sat here all night credit card in hand ready to order the tosh then with reading more posts on rainbows, blurring etc it does kinda put people like me off when really i should be basing my thoughts of buying it on MY albiet limited experience of viewing it
    its late now but first thing in morn 1 order for 1 toshiba is going in because at this rate sky will have hdtv before i have a set!!!!! :D
  3. Delboy


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    Well, mine comes....ooo today pm....TBH i watched it at comet, watched the sagem, didn’t look for the rainbow effect (didn’t know about it), and cant say im that worried about it. Down here its almost impossible to get a demo of TVs, people haven’t got the time to waste on customers. Ive got a grads worth of Panny CRT here, all the reviews rate it 5 star, and tbh its crap. My old tosh 28 was way better. This panny, when you watch DVDs, in dark places its almost a dark blue. None of the edges of things are a clean cut, almost a shimmering around writing, and its like motion blur with it on some occasions. I work in IT, so i see a lot of pixel faults with LCD screens, and im think im right in saying that if you have pixels gone, they are not covered by any warranty from the manufacture, unless they are grouped (normal 5 at least) in one spot. So LCDs have potential problems. Plasmas i gather can suffer from screen burn. RP looks way too grainy in my opinion, so what are we supposed to do. I really think manufactures don’t know which way to go, and with so many choices for under 2 grand, what is the right choice. I for one will stand in awe of the tosh i think. If i get this blur, then i shall be on to Tosh or comet, cos long term, you could say that it affects you vision. This our my own thoughts on this, and even tho most say they have the blur, they still love the TV.....Surly that says it all doesn’t it?
    :lesson: over.....12 hrs to go....hmmm sleepless nite ahead i think... :D


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