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Which is more important for Bright and clear picture Lumen , Contrast Ratio ?

Discussion in 'Projectors, Screens & Video Processors' started by Jazzartist, Jun 3, 2003.

  1. Jazzartist

    Jazzartist
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    Hi folks ,

    I have been trying to get a clear answer for this question for a while , but I am yet to find a satisfactory explantion. As I am new in the projcetor thing I am not much familiar with everything . If this question is already discussed then let me know about that thread . Thanks in advance .

    Jazzartist
     
  2. Anders_UK

    Anders_UK
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    One is not much good without the other!! Lumen in itself is just the light output from a source, you really need to calculate the 'Iluminence' of the screen from the source, then from your screen characteristicts - gain curve, you can work out your picture 'Luminence'. However you can have nearly 50-60 FL on a typical home cinema screen, but without a decent contrast ratio the picture will look naff. Most fixed matrix PJ's will have a sequential ratio of around 100:1 regardless of the ANSI or full on-full off figures. Your eye is more adapted to picking up brightness variations than colour - hence the start of different video formats.
     
  3. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    As Anders says you need both but it doesn't stop there.

    Even with a large contrast it can still look crap. Colour gamut and the ability to show different graduations of luminence and colour are critical too. Specs are, on the whole, pretty useless when deciding what to buy. Your eyes are, on the whole, pretty useful.

    Gordon
     
  4. Mr.D

    Mr.D
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    Its all about the disclosable intensity range to differentiate this from contrast range:

    Contrast range is the difference between the blackest part of the image and the brightest part. ie a sheet of white paper with some type on it has a huge contrast range but an intensity range of effectively 2 ie full black and full white and nothing in between.

    What you need to ensure is that the display is capable of representing the full intensity raneg of a video image : the 100 to 1 figure is about ok for video. This should allow the image to be displayed without any crushing ( you'd get posterising).

    Video has quite a measly intensity range ( characterised by little black detail and fairly harsh crunch off in the whites) so it relies on having a fairly large intensity range on the display to map the available intensities into ( ie a CRT type intensity range of about 1000:1). This allows the perceptable differences between black point and the mid tones and the whites to be quite large which translates to an aesthetically pleasing image.

    The problem with a lot of digital display devices is that they lack this nice healthy intensity range to map to so the image is displayed with the intensities mapped much closer to each other. Less perceivable differentiation in intensity level equates to a flatter less punchy image which equates to less sense of depth even though all the available intensity range is on display. Couple this with a higher than optimum black point and you end up with even less margin for error in producing an acceptable image.

    Things that will help get the best image possible are: decent calibration paying particular attention to black and white point and gamma.
     
  5. Jazzartist

    Jazzartist
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    Thanks to Gordon, Mr. D, and Anders.This helps somewhat . Can you guys suggest some specification as to How many Lumen , Contrast Ratio, Pixel is ideal for a room size of 20 feet by 20 feet with medium size audience consisting of family members and dimly lit room.

    Jazzartist
     

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