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CRT projectors - 30,000:1 constrast ratio!

Discussion in 'Projectors, Screens & Video Processors' started by cyberheater, Nov 30, 2004.

  1. cyberheater

    cyberheater
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    I can't believe that these things can deliver that kind of contrast ratio and still be as bright as that.


    CRT projector


    We're all raving about modern DPL/LCD but it seems that they've still got a long way to go.

    What is the contrast ratio on a normal TV then?
     
  2. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    It's got to be very very hard to measure the actual contrast of a CRT PJ. The fgure they quote is obviously for full on/full off but with a PJ like that one the actual amount of light coming out when displaying black is going to be very hard to pick up with a light meter. The key to getting extreme contrast measurements like the ones they state is getting black as black as possible. It's easier to do that than increase light output.

    The on/off contrast of a CRT TV is going to be huge too.

    ANSI contrast is possibly a better measurement of realworld contrast but even that doesn't tell the whole story.

    There's alot that goes together to making a great image and although CRT is huge and requires specialist set up they do still offer astounding picture quality which is probably why they continue to be in demand for critical imaging applications.

    gordon
     
  3. theritz

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    ........ like showing movies for us !!!


    Sean.
     
  4. Gary Lightfoot

    Gary Lightfoot
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    You may actualy find that in order to get good shadow detail from a CRT projector, you need to raise the black level floor - this means raising its' brightness so you can actualy see what's being shown at the very darker end of the display, rather than it all appear just as black to your eyes with little discernable detail.

    Raising the black level of course reduces theoretical contrast - any lumen number divided by zero will equal infinity (a CRTs theoretical CR because it is able to emit no light when 'projecting' black), but when you increase the black level to reveal detail you then reduce the contrast ratio. The more you need to do this, the more CR you lose.

    A perfect example of this is when William Phelps (a well known calibrator in the US) calibrated a Sony G90 - he could get any contrast number he wanted at one stage (as Gordon says, light meters become unreliable at extreme levels of darkness), but after setting black level so that details could be seen, he ended up with about 8500:1. The Sony G90 is considered the pinnacle of CRT front projectors so this isn't a reflection of a poor performance, merely a compromise over theoretical figures and actual real world requirements for a good image.

    I can probably find you a link to avs where I mention this and almost cause a fight. :p

    ANSI contrast is one area where DLP is now able to beat CRT in the image stakes though - it's measured while displaying both white and black squares simultaneously on screen. With a CRT, the light can scatter in the lens and wash out the black somewhat and this is true in practice. This doesn't happen to the same degree with digital pjs. ANSI is also influenced by the room, so dress like a Ninja when taking measurements and make sure the walls are dark. :)

    I think that as there are more examples of scenes displaying both light and dark images rather than just pure black, the ANSI ability of a pj is probably of more importance. However, there are many that feel that even with this advantage, the ability of true black and a larger CR gives an image a bigger improvement overall.

    Gary.
     
  5. cyberheater

    cyberheater
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    Interesting. So a PJ with 10,000:1 contrast is really as good as you'll ever need. The Sony LCD PJ with 6000:1 contrast is not that far away.
     
  6. windfall

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    According to some sources there are some consumers here in the UK taking delivery of their HS50's so lets await their "reviews" and see what the score is.

    Heres to hoping!

    Tone
     
  7. Tempest

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    The last time I went to a cinema (after owning a LCD projector where blacks are greys) I make a point of looking at the quality of black blacks (never bothererd before)

    I was actually supprised to see in the cinema just how grey the blacks were on the big movie screen.
     
  8. Nick_UK

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    They've been using these projectors on Jumbo jets for years. The biggest problem with them is keeping them in convergeance.
     
  9. Gary Lightfoot

    Gary Lightfoot
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    I think the new Sony has a CR of around 1400:1, which becomes around 4000:1 (when calibrated) with the dynamic iris - some are calling it 'dynamic contrast' to distinguish it from ststic on/off contrast.

    I think in some scenes, it still can have the old LCD grey look about it, but the overall impression seems to be good. I've not heard of any VB issues either, so this new dynamic iris could be the the next device we see incorporated into many new pjs in the near future.

    Tempest,

    I did the exact same thing when I went to the cinama after getting my first pj, and came to the same conclusions. Blacks aren't blacjk there either - it's always going to be tricky with a pj that has has a bright lamp in it imho.

    I've also heard varying figures regarding the contrast of film, some saying it's as low as just 1500:1, which means that in that case most of us can achieve the same or better at home.

    Gary.
     
  10. cyberheater

    cyberheater
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    Yeah. I was on a plane to Canada last year where they had a couple of 3 tube projectors on board. I would have been fine but the folks kept insisting that they keep their light on :rolleyes:
     
  11. cyberheater

    cyberheater
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    I really do hope so 'cause my new PJ that i'm getting tomorrow has a CR of 2000:1. I'm hoping that that's not marketing bull.
     
  12. Gary Lightfoot

    Gary Lightfoot
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    Unfortunatley most CR claims are to a degree - those are normaly uncalibrated numbers.

    Most lamps are red deficient, with blue and green being higher, but shipping them like this means they can quote higher contrast figures for it. When you calibrate them, you have to lower the green and blue contrast so that it then matches the red so that you have balanced colours (idealy to D65), but this reduction of contrast results in a reduction of lumens, so the contrast ratio drops.

    Using a filter to opticaly correct a pj is better because you balance the colours without having to make large reductions of colour in the pj, so contrast stays higher.

    What pj are you getting?

    Gary.
     
  13. windfall

    windfall
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    Gary

    Please excuse my ignorance but the calibration process you mention (and other have too) what process are you talking about? Is this where you get a DVE or Avia disk and use the test screens or do you mean getting a light meter as well?

    Excuse my ignorance!

    Cheers

    Tone
     
  14. cyberheater

    cyberheater
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    BenQ PB6100 :)

    I've been reading tons of stuff on other forums about it. 99 percent positive.

    I hope is going to be a reasonable step up from my AE200.
     
  15. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Forget contrast ratio as a means to meaure performance. You can have a high contrast by using a light canon PJ. For domestic use this would be not much fun.

    Undoubtedly most films have scenes where there are bright and dark areas with detail. With most CRT's a compromise has to be made as to what level brightness is set as they do not keep black at the same level dependant of the average brightness of the picture content. What most CRT users do is adjust brightness so that in dark scenes (low apl) you see detail but the image is still dark. This would generally lose detail in the dark part of the image during bright scenes. The alternative is how Gary has mentioned WM did one of his measurements. This is to set black level with a higher apl signal. This results in lower on/off contrast and a washed out look to dark images, pretty much like LCD and other fixed pixel devices can usually look (this is a joke by the way before anyone comes hunting for me)

    Ideally we want black blacks and high ansi contrast too. One day, one day!

    Gordon
     
  16. cyberheater

    cyberheater
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    I hear you. I hear you :)
     
  17. Gary Lightfoot

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    Tone,

    to do a proper colour calibration, you'll need an instrament that can (idealy) see light in the same way as the human eye. They're often referred to as colorimters IIRC, and have colour filters built in to try and do just that.

    Using a test disk to display different levels of grey is how we can measure the colour balance - we call these grey fields 'ire' levels, and are often represented in graduations of 10 and complete screens of each ire level. Zero ire is black, 10ire is a very dark grey, 20ire is a slightly less dark grey ect all the way up to 100ire which is white. Grey is just a balance of all the clours (R, G and B), and if correctly balanced, the greys will appear as just that - grey, and not have any colour tints in them. You display a grey field such as 30ire, and use the colourimiter to measure it. It will tell you (often via software like Colorfacts) what colour(s) is high and which one is low. You then use the projectors seperate RGB controls to adjust the colours individualy until the balance is right for 30 ire. You then do the same again for say 80 ire. Then go back and recheck 30, then 80 etc until they seem right, and then do a complete greyscale from 0 to 100 to see if all colours are balanced across the board. You may need to tweak it more if there are variations.

    This is where you will normaly see the red being lowest (at 100ire where red cannot be increased to meet the green and blue), and why you have to adjust the green and blue down to meet it. In doing this, you will lose contrast, so the figures you will normaly see advertised (unless specifically stated) will be in an uncalibrated state.

    Again Gordon hits on an important point - black level and contrast aren't necessarily related. Some pjs can improve the contrast by fitting a higher output lamp. The black level will raise as will the white level, but the contrast ratio can go up. Some projectors like the Infocus X1 have a white segment in the colour wheel which boosts light output. The contrast for that mode is stated at 2000:1. That's normaly a data mode. When you put it into video mode, it switches off (doesn't use) the white segment, and the contrast ratio for that mode is stated at 1400:1.

    HTH

    Gary.
     
  18. windfall

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    Hey Gary/Gordon

    Thanks for that!

    About 20 years ago I did O level photography and TBH I should know some of this, but girls, computers, divorce and home cinema have dulled my mind somewhat!

    I have heard some people say that they have "65k callibration" what is that about exactly? Is that a colour temp that is used?

    Tone
     
  19. theritz

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    The "65k calbration" refers to setting the colours on the projector to achieve correct white balance. Daylight has the same colour as a chunk of platinum heated to 6500 kelvin, which is where the term comes from.


    Sean.
     
  20. Gary Lightfoot

    Gary Lightfoot
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    That's another interesting piece of info!

    I've seen this black line refenced on CIE charts as the 'black body curve'. I thought it was a theoretical material that when heated, would glow at a certain colour (didn't know what the material was). Along the curve you will see various reference points, and Daylight 65kelvin (D65) is just one of them. It also mentions a Planckian locus. Damn those insects. :)

    Years ago, 4800k was the reference for movies - black and white movies though IIRC.

    The reason we use D65 is because it's the reference to which films are made, so if you want to see the colours acurately depicted on your display device, it should be calibrated to D65. The Matrix may have been done differently. ;)

    Of course, not everyone knows or cares about D65, so, as long as the picture looks good to you, that's what's more important. I even know someone who actualy likes to tweak his displays away from a calibrated D65 because he prefers a different look.

    Here's a link for those who may be interested:

    http://www.ledproductstore.com/colorimetry.htm

    The CIE chart is near the bottom.

    Gary.
     

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