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What's The Difference Between DLP and LCD?

Discussion in 'Projectors, Screens & Video Processors' started by gwbailey, Feb 4, 2001.

  1. gwbailey

    gwbailey
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    Help anyone?
     
  2. RanjanB

    RanjanB
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    DLP is a newer and completely different technology.

    Advantages of DLP over LCD are:

    - You will never suffer any dead pixels
    - Usually get sharper reproduction of blacks

     
  3. LV426

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    An LCD device creates the image by shining a bright light through either one, or more usually three, LCD panels - these are rectangular arrays of pixels which can be made to go dark, transparent, or any state in between. The picture is formed by controlling the transparency of each of these pixels. In a 3-panel device, each panel creates the red, the green, and blue components of the image which are then merged optically to create a full colour image, which is then projected through a lens. The number of pixels per panel depends on the device. The Sony VW10HT, for example, has a million pixels in each panel. During manufacture, if an LCD crystal itself, or the tiny transistor that drives it, fails, you get a bad pixel. If it's permanently transparent, you get a bright pinprick on your screen. If it's permanently dark you won't see it.

    DLP devices work similarly, except that, instead of light shining through LCD arrays, the light is reflected off an array of tiny mirrors. These tiny mirrors are tilted to give anywhere between full brightness (the mirror reflects the light straight into the lens) and full darkness (the mirror reflects the light away from the lens) and anywhere in between. DLP arrays are expensive. As a consequence, all "normal" DLP projectors only have one DLP array. The colour image is created by sequentially energising the array with the red, then green, then blue components (maybe not in this order). Synchronised with this is a coloured wheel that spins in front of the array. So, when the blue component of the image is on the array, at the same time, a blue filter is in front of the array. So, the picture projected is, actually, all blue, all green, then all red. All this happens so quickly that your brain merges the three colours into a full colour image.

    DLP gives better black levels than LCD because you're not trying to shine a bright light through something dark - LCDs never can go completely opaque - whereas DLPs can easily reflect the light fully away from the lens. BUT - with single-chip DLP's you can, sometimes, see the effect of the sequential colours - manifests itself as rainbow effects around fast moving objects (or if you scan your eyes across the screen).

    Also, AFAIK, nobody makes a true 16x9 DLP chip. So all DLPs are intrinsically 4x3 - which means that, for the majority of DVDs which are wider than 4x3, you're "wasting" resolution in black bands top and bottom. Most LCDs are also 4x3. However, the Sony VPL-VW10HT has 16x9 LCD arrays which make better use of the available pixels to produce your picture.
     
  4. gwbailey

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    Thanks Nigel, You know too much!!

    Just out of interest, what projector have you got? (if any!)
     
  5. LV426

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    I'm a completely satisfied Sony VPL-VW10HT user. Chosen because I have a real "down" on CRT devices, for reasons I have aired elsewhere in this forum, and because I can see the DLP rainbow.
     
  6. BadAss

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    Nigel, that was some explanation!
    I'm currently saving up for a projector and had but the Sony10HT in mind, but recent views Ive read on the the greyish blacks the Sony gives have slowly put me off.
    Just how good or bad is this projector?
    Should I wait for somthing else as it will be later on this year when I buy.

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  7. lmccauley

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    BadAss,

    I would recommend you definitely check out the Sanyo PLV30 - it has much better blacks than the Sony, a picture that is just as good or better and costs around £2100. It is a bargain.

    Cheers,
    Liam

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  8. lmccauley

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    This is one of the points that makes me pause before rushing out to buy a Sanyo.

    I agree that the black level wouldn't cause a problem when watching a lot of programming - your eyes compensate and the greys do look black most of the time. However, what I saw in a side by side comparison at StereoStereo was that the Sony did miss a lot of detail in dark scenes. This definitely spoiled the opening scene in the Matrix for me. Since a fair few of my favourite films and TV programmes (Buffy, Angel) tend to be dark, this makes the Sony no good for me.

    I completely agree with these points. You *need* to get a good demonstration of these projectors to see what suits *you*. I discovered that I'm sensitive to the rainbow effect inherent in DLP projectors after being demoed the Sim2 HT200, so it is no good for me. Also, other requirements ruled out CRT - it doesn't matter how good a picture they produce, they're no good for *me*.

    Cheers,
    Liam

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  9. Mr.D

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  10. Mr.D

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    It is really. In theory you'd need a material that had less of an effect the brighter the light passing through it. You'd need some exotic smart material that was capable of changing its properties back and forth at pretty much the speed of light. thats not necessarily against the laws of physics but the material doesn't seem to exist! ( like polaroid glasses in reverse but really quick which might really go against the laws of physics as polaroids use the energy of the absorbed light to drive the darkening)

    Probably worth a mint if you managed it!
     
  11. LV426

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    I should have said...... the other reason I chose the Sony is because (at the time) it is (was) the only widescreen unit available. All other projectors are (were) intrinsicallty 4:3 - which means a compromise on your screen size and/or available resolution for the majority of DVDs you'll be watching.

    Black levels is a subject much aired in this forum and seems to be the main argument against the Sony and other LCD machines.

    My own opinion is that they are not that bad and you get accustomed to it. For me, the artifacts introduced by other technologies are more intrusive.

    Contrary to popular comment, a properly set-up Sony WILL NOT loose detail in dark areas. It will, however, show dark areas as a dark grey, rather than true black.

    At the end of the day, I can only give you my opinion. Each one of us has slightly different visual acuity and will see things that others don't. For me, I do see image flicker, DLP rainbows, etc., and cannot stand bad geometry, stability or convergence. I can, however, cope (easily) with grey blacks.

    One thing I can say, is that, often, something which gives an immediate, subjective "good" impact can often become intrusive after extended use. And vice versa.

    I would concur with other correspondence that, on demonstration, a DLP machine might give a better subjective impression than an LCD one. It was only after some time that I began to find the flickering multicoloured image annoying. Fortunately, I spent this time in a demo room before I parted with my cash.

    You really need to do the same.

    Again, my opinion is that the VW10HT is, for me, as good as it gets, at present.
     
  12. LV426

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    "Won't loose detail in dark areas" - this comment is based on

    (a) comparison with the same picture displayed on a regular CRT TV

    (b) Use of THX Optimode test signals.

    BUT it must be properly set up - with the correct brightness and contrast levels for this to be true.

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  13. Gordon @ Convergent AV

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    Nigel:

    The Sony, Sanyo and Sim2 were all set up using the Avia test disc. It has the necessary patterns for setting brightness and contrast properly on fixed panel displays. The Video Essentials pluge pattern isn't really suitable for use with these as they don't "bloom" when contrast is too high.

    Gordon



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  14. LV426

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    Gordon:

    I have absolutely no doubt that your demonstrators are set up to the highest possible standard.

    If I gave any other impression, it was not my intention. I was simply responding to Mr D's question regarding my "no loss of detail" observation.
     

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