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Alarming information on "actual" front projection CR!!

Discussion in 'Projectors, Screens & Video Processors' started by Kramer, Oct 7, 2005.

  1. Kramer

    Kramer
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  2. PJTX100

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    I'm alarmed... :D
     
  3. Timbo21

    Timbo21
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    !!*?? :confused: ??!* :eek: *?*! :rolleyes: :devil:
     
  4. monopole

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    200:1 - that's ANSI contrast - roughly, put a black and white checkerboard pattern on screen and measure the brightness of a white square, then the brightness of a black square. Take the ratio and voila.

    Having white walls will destroy ANSI contrast. The contrast you usually see quoted with a projector is on/off contrast ratio (i.e. measure the brightness of a fully white image, then measure the brightness of a fully black image and take the ratio - this is around 2000:1 on the newest projectors)

    However, the eye isn't very sensitive when it comes to ANSI contrast since it has an iris which causes the pupil to dilate (when an image gets dim) and contract (when the image gets bright). So getting back to the checkerboard, even if the black square is quite grey, it will still look black to the human eye in this setup (because the pupil will be small, limiting the amount of light that can get in). This is why an adaptive iris works so well on a projector - it's doing exactly what the eye does (ok, not exactly, the eye doesn't boost gamma with a low lumen image to bring out the shadow details - well, not yet anyway :)
     
  5. Tempest

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    Interesting :)

    OK, so I'd be interested to know this:

    As we know about the human eye and the fact it's good at the DIFFERENCE between things rather than the absolute colour/brightness of things (correct me if I'm wrong here)

    But anyway.

    If you have a bright scene, then the blacks look nice and black, as there is white on screen (the chequer board is a excellent example of how to fool the eye)

    But what kind of contrast would we need (if that's the right term) so if we are watching a space film where the screen is almost all black with just a few points of light (stars) and perhaps a space ship in the distance, then what would we need, so these points looked bright against a lovely jet black background (as opposed to the poor grey we seem to have with LCD and (perhaps a slightley lesser extent) DLP machines?
     
  6. Knyght_byte

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    just get the projector, watch the film and enjoy it damn you! stop being picky!!...hehe ;-)
     
  7. Kramer

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    200:1 max contrast ratio from current front projectors!!! The average D5 LCD seems to be around 6000:1 (with DI).

    Top end DLPs around 4/5000:1 (no DI gimmicks :D ).

    Have we all been duped as Stuart suggests? ALL victims of "marketing BS"?

    Really, really surprised this has gone down without much debate. I for one think it's been over simplified.........could say more......

    If the max we humans can "see" is 800:1, what point in manufacturers quoting 5/6/10/20000:1? Don't think we can differentiate between 10s of millions of colours either :eek: .

    What's with respected reviewers quoting 1800:1 @ D65 (Z4) etc. if the actual figure is approx. 200:1? Gary L's measurements etc., all meaningless? That would make everything since the AE100 a product of "marketing BS"??

    Have you been a victim of "marketing BS?

    :D
     
  8. Gary Lightfoot

    Gary Lightfoot
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    I think Monopole has hit the nail on the head as 200:1 is obviously wrong! ANSI is room related and it may be quite true that even if a pj is capable of achieving over 500:1 ANSI, the room may limit this to 200:1. That is quite different to on/off contrast which is not room dependant.

    As posted on the poll site:

    "I've actually measured my Optoma H78 at 2707:1 and my NEC HT1000 at 2000:1 (both at D65), so I beg the question where does 200:1 come from...

    Film in general is around 2000:1 unless some procesing of the print is made to increase it - usually by improving the ability of the black celuloid using a nitrite process IIRC, and this may give you around 4000:1.

    That might all be a moot point since the film/Hi Def cameras that record this to film or tape are only capable of 1000:1. Any higher CR than that will just improve the black level from a given white level, and will not reveal any more shadow detail.

    I believe the eye/brain is able to assess more than 800:1 IIRC but I'll try to find the details...

    Gary.
     
  9. Tempest

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    I may be talking out of my arse here (possibly not the 1st time!)

    But is it not possible (or important) to measure the black level when the projector is running but nothing is on screen?

    I mean, pitch black room, turn on projector (few mins to warm up) displaying a totally black image then measure how much off of black it really is?

    Any white (or anything) on screen will distort this reading and make the black look better as it will

    A: give contrast for your eyes/brain
    B: light the room/area to reduce the blackness of the white screen.

    So, will/can/does anyone actually do this (with a light meter or whatever)
    I knowon mine (and I guess everyone elses) projectors, sitting in a pitch black room, with your projector displaying black, it's so dead easy to see the grey screen running.
     
  10. Gary Lightfoot

    Gary Lightfoot
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    The correct way to measure contrast is to project a full white field usually derived from a test disk or an image generator and measure that at a fixed point in front of the pj (say 3ft in front), then project a black image in the same way and measure that. You then divide the black measurement into the white and that is your contrast ratio.

    Ideally you should do this at D65 because then the pj is calibrated for video and you have used a universal standard that can be compared on equal terms with other projectors. If you use a DVD player and a test disk then you are measuring genuine conditions that are representative of what you will be viewing on your display, so the CR will be an accurate and real world measurement of what the display is actually capable of.

    What manufacturers tend to do is to push up the RGB contrast settings so that you have a very blue/green image (red is deficient from the lamp), and then push up the common contrast control to give you the brightest white you can have. If white peaking is present, they will turn that on too. For black they will ramp down the brightness setting so that you have the blackest black possible, and the image you will now be presented with with have no bright or shadow detail and appalling colours. It will be basically unwatchable. That's when they take the black and white measurements and those are the figures you see for lumen output and contrast. Only Infocus give true contrast ratio readings, but even then I think they use white peaking which is not ideal for movie watching.

    It's relatively simple to take a contrast ratio measurement with a light meter but it's a little more difficult to ensure you are at D65 when you do it. With SpyderTV at under £200, and a spread sheet available that will help model the readings into something you can use to make adjustments, it's becomeing cheaper to do this. It just needs some knowledge of how and why to make the adjustments but it can be quite simple once you get the hang of it. It does need more knowledge and experience when things don't turn out right and something needs to be remedied though.

    Full white and full black are generated using a test disk like AVIA, DVE, Peter Finzel or the new downloadable DVD from AVS. They're often referred to as 100IRE (white) and 0IRE (black).

    ANSI contrast has already been explained and is a reading taken when both black and white are being prjojected as black and white squares on the screen. It not only measures the projectors capabilities (it's lens or display array for example), but also the room itself and how much light it allows to reflect back onto the screen from the walls etc.

    HTH

    Gary.
     
  11. gandley

    gandley
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    I dont think 200:1 is the best for current ANSI contrast.

    I read somwhere on the Avsforum that someone had measued the H79 at 900+:1 ANSI contrast with around 2900 full on/off.
     
  12. Kramer

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  13. Gary Lightfoot

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    ANSI can easily be as little as 200:1 if the room is somewhat reflective (even with grey walls), but if you cover the screen with black felt and measure it again, it will be considerably higher (400:1+). The screen reflects a lot of light, and the room will reflect it back and wash out the black areas. That's why dark non reflective surfaces are best if you have the choice.

    I've seen measures of between 600:1 and 700:1 mentioned over on AVS by Darinp2, and the 2900:1 CR for the H79 was from Greg Rogers measuremnets from Widescreen Review. I'll dig it out and see if he'd taken an ANSI reading.

    Gary.
     
  14. Gary Lightfoot

    Gary Lightfoot
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    The Australian website's data for the Human eye is flawed IIRC, and they have been requested to correct it on a few occasions IIRC. The 300:1 doesn't correctly relate to what we can actually determine but I'll try and find the correct details that had the info on why it is wrong.

    Here's a link:

    Gary.
     
  15. Gary Lightfoot

    Gary Lightfoot
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  16. gandley

    gandley
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    Nice find gary. Hope you stuck this in stuarts thread.
     
  17. Gary Lightfoot

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    Thanks,

    I haven't but I guess I could. :)

    Gary.
     
  18. Tempest

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    I do have a question which is (kind of - -in a way) related to all of this (sort of) so thought I'd keep this in this thread.

    I've not actually seen in the flesh one of the current LCD machines that have this dynamic iris (which the next machine fine tune a bit more I guess) so I'd like someone to try and answer this for me.

    As I understand it, you have a bright scene, the iris opens up you get a bright picture.
    But if you have a scene with a lot of black, the iris closes down and you get a darker picture.

    Is that basically what happens?

    If this is so, you can guess my next question............

    Do you actually notice this happening?

    If you have a mostly back space scene with a few bright stars and a space shipm you you get blacker space but also duller stars and space ships?

    Do you notice the blackness in one part of a dark background changing when something bright comes on screen at another position on the screen.

    I guess obviously, we'd love bright stars and spaceships on a jet black backdrop, but I suppose that's asking to much.

    Can anyone give a kinda overview as to what it's like when this is happening?

    thanks
     
  19. Gary Lightfoot

    Gary Lightfoot
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    Sounds about right to me. In some scenes with some machines (the HS50 IIRC) it has been said that you can see the iris work, and sometimes it gets confused apparently. I think they also adjust the gamma accordingly so that the luminence of the scene is raised as the iris shuts so that detail is made more visible.

    I've not seen it myself, but it does do a good job most of the time I believe, and it will now be interesting to see how well newer machines with similar dynamic iris do this.

    Gary.
     
  20. MikeK

    MikeK
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    Gary, out of interest, have you ever measured the ANSI contrast of your H78 under the same conditions?
     
  21. Gary Lightfoot

    Gary Lightfoot
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    Yes I have - it was approx 100:1 using the AVIA ANSI test pattern, and 400:1 with 80% of the screen covered, so in ideal conditions, I would expect something closer to 500:1.

    Where my ANSI is being comprimised is the closeness of the sloping ceiling to the screen. It may be a little better with the screen a bit lower now,but I'm going to be experimenting with blacking out the front 5/6ft of the room and will then measure it again and see how it goes. I can see the effects of the reflected light on the blacks near the edge of the screen, but with the room being 18% grey, the effect is less visible than it would be if the walls were a colour.

    Gary.
     
  22. DEANO-B

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    I found when I demoed the Sony HS50 the Dynamic Iris to be too strong - in other words it seemed to overly darken the whole picture when a lot of black was present and gave the picture a dull effect. It was to me, a very diisapointing experience to see a picture that wasn't as punchy and vived as my AE700 (I'm sure many will disagree) and makes me a little worried about the new batch of LCD PJs. After I demoed the Sony I looked at a few reviews which agreed with exactly what I have described.
     

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