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An Amoeba Question

Discussion in 'Projectors, Screens & Video Processors' started by MATT JENNER, Jul 26, 2003.

  1. MATT JENNER

    MATT JENNER
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    Hi

    Even though i am involved with crt, i do have to ask what the contrast ratio is all about,

    when they say 1000 to 1 what does that mean ?

    and on dlp they say 1600 to 1 ,

    probably a complete thikko question and i will kick myself when i see the answer

    Matt
     
  2. RichardA

    RichardA
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    Hi Matt,

    Contrast Ratio is simply the difference between the brightest the projector can acheive and the darkest it can acheive.

    That's the simple bit, but defining how you measure the brightest and the darkest is the difficult bit.

    For CRT type displays which actually generate light, the darkest that can be acheived is effectively 0 (i.e. no light) though in real installations a little light can be generated. The maximum light output from a CRT depends upon how much of the face of the CRT is at maximum (a small area of CRT being illuminated will be brighter than illuminating the whole face).
    Usually the measurement for CRT will be with a small area of the screen at maximum illumination (about 10% area).

    For LCD and DLP the difficulty is reducing the lamp brightness to represent black, while producing white is pretty easy.
    For these types of projectors there is two types of measurement - full-frame and ANSI.

    Full-Frame takes one measurement from the centre of the screen of a full white screen and then a measurement from the centre of a black screen. Divide one by the other and you get he maximum contrast ratio possible.

    ANSI uses a 4x4 checkerboard pattern of white and black squares. 16 measurements are then taken (one in the centre of each square) the total of the 'white' measurements is divided by the total of the 'black' measurements to give the ANSI contrast ratio.
    The ANSI measurement is a much more realistic representation of real life as it takes into account the flare within the lens.

    The closer the ANSI measurement is to Full-Frame the better the optical path.

    Hope this helps!
     
  3. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Matt: So what Richard is saying is that you do not know the methods used to measure contrast ratio. Even with the method known you still have the problem of whether the fullon/full off or ansi measurements were done with the projector set up within it's real operating range.

    ie Doing either measurement with CONTRAST at FULL and Brightness at minimum will not give the same results as doing them with those parameters set to useable points where no detail is being crushed or clipped.

    As with most specifications they are open to loose interpretation.

    Gordon
     
  4. MATT JENNER

    MATT JENNER
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    thanx guys for the help

    Matt
     
  5. Roland @ B4

    Roland @ B4
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    Typical CRT will produce about 1000:1 ANSI contrast ratio
    Typical LCD about 500:1 and DLP about 700:1

    If you were to use the same method as curretnly chosen by the lamped projectors CRT would achieve about 30,000:1

    they can't mach the picture quality so they try to do it with the specifications
     

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