I still don't get the Contrast setting

Discussion in 'Beginners, General Questions' started by Todd K, Feb 28, 2005.

  1. Todd K

    Todd K Second Unit

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    OK, I own the digital video essentials DVD, and also came across a 2004 article that was published in Stereophile Guide to Home Theater managize discussing calibration.

    They both talk about turning up the contrast on the Pluge Pattern w/Grayscale until you see blooming in the whitest box. They caution that on some displays (mine being one) that you really never seem actual blooming. There is also a ramp pattern (chapter 12-14?) they say you can use to adjust contrast.

    For these tests you're supposed to turn contrast up until you get a blooming or distortion effect, then turn it down below that. To my understanding, this would be the HIGHEST acceptable point for contrast. But what is the LOWEST acceptable point? I don't know how you're supposed to figure that out. (possibly because DVE doesn't tell you what you're supposed to do with half the patterns they give you?)

    I also have the THX demo that comes with various DVDs, and they give you 8 white boxes. Again, they say you're not supposed to set it so high that you can't distinguish the boxes from one another. But how low beneath that should it be set?

    Right now, my contrast is set higher than my brightness. Should this be the case? Over the weekend I helped to set up a friend's TV, and I ended up with the brightness being set way higher than contrast. For properly set displays, is one always generally higher than the other, or can it vary?

    Thanks for your attention to this post. If there are tests (especially ones that can be used with specific DVE signals) for setting this properly, I'd certainly like to know about them.

    Regards,
    Todd
     
  2. Ted Lee

    Ted Lee Lead Actor

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    i'm not positive, but i don't think you want a low point. the whole idea of contrast is to get the most "separation" between the whites and the blacks -- without blooming???

    as for the thx optimizer thing, my understanding (again not positive) is that those are optimized for that *specific* dvd only - so it's not a good idea to use it as your primary calibration tool.
     
  3. Jim Mcc

    Jim Mcc Producer

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    Todd, what kind of display are you setting? If you have a DLP, you will not get blooming. Your contrast should not be above 50% generally. With the THX disc, you raise the contrast until the boxes start to blend together, then reduce it 1 click. You should see 8 distinct shades of white. You need to set contrast first, then brightness. I calibrated my X1 projector with Avia, then checked it with a THX disc, and the contrast and brightness were the same.
     
  4. Todd K

    Todd K Second Unit

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    I have a standard def sony wega CRT set. On the THX disc, I can turn it all the way to the max, or all the way to the min, and I still see all 8 boxes of white. Even as I increase the setting they never really seem to blend together.
     
  5. ChrisWiggles

    ChrisWiggles Producer

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    Todd, this should help:


    http://www.hometheaterforum.com/htfo...light=contrast

    On a CRT, you want to prolong the life of the set by using a low white level setting, while still maintaining whites as appearing, well white. As described and illustrated in Avia, you may observe color shifting or blooming at high white level settings on a CRT, as well as geometry distortions. Most importantly you want to be well below the point of blooming. you have to observe the scanlines closely to see blooming (loss of focus of the electron beam).


    The numerical settings are really irrelevant, they have no relation to each other, nor any relation to on other displays, or even the same model display.

    Basically, the easiest thing to do is make sure you aren't blowing your whites to the max, and set your whites as low as possible, so that they still appear white. This will be much dimmer than out-of the box settings, and may be dimmer than you are used to.
     
  6. Todd K

    Todd K Second Unit

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    This part I understand, but exactly HOW FAR below the point of blooming you're supposed to be puzzles me. Say if I turned the contrast up all the way to like 95% and just noticed the blooming. If I decreased to just below the point of blooming, I doubt I should set the contrast at 94%, since that seems way too high.

    Are there patterns on any of the test discs that say "turn the contrast down until xxxx starts to happen?"

    Like maybe chapters 12-14 and 12-15 on digital video essentials? I have a feeling those are useful for setting contrast, but have no idea what to look for when using them.
     
  7. Brian L

    Brian L Cinematographer

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    Ideally, you want it a click or two BELOW the point of blooming. That would be your maximum safe white level.

    Myself, I can't get my set (a Pioneer 533 CRT based RPTV) to bloom, I do not get any white crush like the digital display guys do, and I do not see the scan lines blur.

    Joe Kane has indicated that you will see a slight color shift in the white areas when contrast is to high, but I have not been able to detect that either. I am sure it is happening, but I think you really need a light meter to know when it is happening.

    So, I just set Contrast to the MAX and call it good.

    Note: THAT WAS A JOKE. DO NOT DO THAT!

    Seriously, what I have found to work OK is to use the Needle Pulses and Steps pattern (this is on Avia and I think Both VE's).

    Turn up the contrast until the black line in front of the white background begins to bend, then turn the contrast down until it is straight, or as close as it will get.

    As you probably have determined, Black Level is a piece of cake to get right, but on many sets, Contrast can be tricky.

    BGL
     
  8. ChrisWiggles

    ChrisWiggles Producer

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    Todd, the reason setting white level is difficult on a CRT display, is that the lower you set it, the longer the longevity of the display, so setting it lower is always best. To set it "ideally" you need light metering equipment to measure how much light output you are getting, and then you can set it to a target number for the proper level of white. Obviously without this equipment, you can't know how bright your display is, and this is impossible to judge by eye, and difficult to find a suitable comparable light source for even comparing by eye.

    If you read the thread I linked, Guy Kuo explains this pretty well.


    As I mentioned, not really. The only way you could state this would be to say "turn the contrast down until you are getting X footlamberts" but obviously you have no way to measure this, and even then this may be pushing some CRT displays too hard if they are worn, etc.

    As guy explains in this paragraph, for CRT displays:

    "So this leaves us with the final portion of my advice for setting contrast - keep it as low as consistent with a good image in a fairly dimly lit room in the evening. If you have contrast high enough to compete with sunlight or bright room lights, you are probably too high. Many people are used to really high light levels from a TV. Indeed, my eyes hurt the last time I saw an RPTV at someone's home because the light output was too high. On a home theater display, the light output when set correctly and viewed with DARK ADAPTED eyes will just begin to feel too bright when the scene abruptly switches from an indoor shot to a bright outdoor shot. That's somewhere around white being about 12 to 18 FL when I measure it against my eyeball "too bright tolerance."

    And:

    " Don't perseverate on looking for blooming or geometry distortions on the test patterns. Instead concentrate on keeping contrast down LOW. Not so low that viewing the picture in a darkened room still results in a dingy image, but as low as still consistent with a bright enough picture in a darkened room. That gives you the best you can do until you have a colorimeter or a pro can come by and get you set up truely right. "

    For anyone else reading, this discussion is aimed at CRT displays. Digital displays should be set differently as they have a set limited(any but those with variable iris) on/off CR range that should be maximized.
     
  9. Todd K

    Todd K Second Unit

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    Now that's the most tangible piece of advice I've heard yet on the contrast issue. Of course the difference between grey and white is subjective, but at least there'll be a smaller range to work with when adjusting (instead of "anywhere below blooming").

    I also have another concern to bring up, not sure if it should be in another thread, but since I'm not sure I can articulate it properly, I'll throw it out there:

    On Digital Video Essentials, they talk about CRT devices not being able to hold blacks at a constant level -- ie, it changes depending on the brightness of the surrounding material. They show with it an image of clouds passing over a desert, and shadows appear on the desert depending on how much sun is out. They say you can also determine this when viewing chapter 12-3, DVD pluge with white.

    I'm not sure if this is happening on my tv, but since it's a 4:3 set with 16:9 mode, I sometimes get two sets of black bars when watching 2.35:1 material. You know, the black bars where that section of the TV is turned off, and the thin bars on the top and bottom of an anamporphic image greater than 1.78:1.

    When the picture on the screen is dark, I get two sets of bars. However, when the picture on the screen is very bright, the bars blend together. Should this always be the case? When I turn the brightness down so low that the bars always blend together no matter what, I start to lose shadow detail.
     
  10. ChrisWiggles

    ChrisWiggles Producer

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    Todd, you are most likely seeing the affects of low ANSI contrast, which is the nature of CRTs (and quite a few other displays and setups too). The bright portions of the picture will wash out the darker parts, obscuring shadow detail. Because CRTs can go completely black, you are left with the compromise of either getting complete black-out, or more shadow details. The choice will be a subjective one. If you use a very low APL pattern to set black level, you will be biased more towards better black, but obscured shadow detail in high-APL scenes. If you use a brighter pattern, then you will have a high black level, but you will preserve shadow detail better. You should experiment to see which you tend to prefer more. On DVE, if you use the pluge patterns with the center boxes, there are patterns at multiple IRE, that will allow you to experiment. On Avia, there is a full-black plus moving bars pattern, which if you use to set black will net you absolute black-out, but poor shadow detail. If you use the half-white plus moving bars, you will have a much higher black level, but you will preserve shadow detail very well even in the most ridiculously bright scenes. This is always a tradeoff.
     
  11. Allan Jayne

    Allan Jayne Cinematographer

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    IMHO the contrast on CRT TV's should be turned down substantially below the blooming point to prolong the life of the TV.

    The "lowest acceptable" contrast level is subjective, according to what you think is good looking.

    When on a 4:3 set in 16:9 mode you see two sets of black bars only during dark passages, try covering up (using cardboard) the brigher parts of the screen and see if you can still detect the two sets of black bars. It is possible the level of the inner black bars could be above true black for that particular movie and therefore you cannot blend the black bars without losing shadow detail. You may have to set the brightness control at a compromise setting. The overall brightness of bright passages may hide the double black bar effect.

    You should, within the restriction above, try to adjust adjust brightness and contrast so that all the steps in the gray scale step pattern are distinct. This should ensure no loss of shadow detail.

    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  12. Inspector Hammer!

    Inspector Hammer! Executive Producer

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    Todd,
    here's what I used to do when I calibrated my CRT monitor before getting the X1 projector...

    Using the white level patteren on AVIA, I would turn my white level down until the entire lower half of the patteren becomes an obvious shade of grey, then I would slowly bring it up until it no longer appears grey, but rather white.

    Then, and I have developed this habit over the years (I consider it standard operating procedure), I would close my eyes for at least a full minuet to allow them to adjust to total darkness, and then open them again and look immediatly at the screen, if it still appears obviously white, that's where I leave it. Of course after I change the black level, I have to go back and do the white level again because they interact.

    Bottom line, forget about starting at the highest point, go the other way and start at the lowest point and work up from their until you hit a recognizable shade of white. By doing it this way it removes the, quite frankly, irritating task of squinting and looking for blooming out of the equasion altogether and simplifies the whole procedure.

    I still do the "closed eyes" technique with the X1, but it doesn't seem to be as crucial as when I had my old CRT monitor. The X1, because it's a DLP projector, uses a different portion of the AVIA test patteren and it's remarkably easy to understand and perform the test.

    Try it, it can't get much easier than that. Good luck. [​IMG]
     
  13. Allan Jayne

    Allan Jayne Cinematographer

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    The significance of the blooming point is that picture quality (sharpness) is degraded.

    You might find that recognizable shade of white is not achieved until you get past blooming, hence the desire to find where blooming occurs, or if it does within the range of your contrast control.

    When trying to find the blooming point, do it quickly, make a note of the approximate setting, and then turn down the contrast since you are in a high screen wear zone.
     
  14. Inspector Hammer!

    Inspector Hammer! Executive Producer

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    I must say that if that is indeed the case, that is one crappy electron beam in that monitor.

    Bottom line is, you MUST achieve white, it is crucial for an accurate image. If one uses the method I suggested, and assuming their electron beam is either of sufficiant or exceptional quality, you should reach the first sign of recognizable white before you even reach the blooming point.

    I've never had a problem reaching white before blooming in any monitor i've ever owned.
     
  15. ChrisWiggles

    ChrisWiggles Producer

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    On worn CRT displays, light output can be greatly reduced, and you may hit the blooming point before you have enough light output left to get a good white. This is not usually the case on any relatively normally used consumer displays, but Allan's point is correct. I do like the way that Avia explains how to find the blooming point, note that as your rough "safe white" zone, and then go on to set white by setting it as low as possible, but to be sure you are below the point of blooming. You will usually end up *well* below the point of blooming as Allan notes, but this isn't always the case.
     
  16. Inspector Hammer!

    Inspector Hammer! Executive Producer

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    I understand, Chris, but part of my point was that if you reach the first sign of recognizable white and your PAST the point of blooming, you have no choice but to leave it there to get white, otherwise you'll have grey and that's not the goal.
     
  17. ChrisWiggles

    ChrisWiggles Producer

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    Well, that's a user decision, but it does mean the set needs to be retubed, or you are trying to drive too large a screen. In any case, I might tend to agree with you, that if the tubes are in poor condition, you might as well drive what's left of them into the ground before retubing.
     
  18. Todd K

    Todd K Second Unit

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    Well, I think I've reached an appropriate contrast level for my set. It seemed like all the tests I ran had me coming back to the same level of brightness, and thus I chose the level of contrast that worked best with the brightness setting. I'm definitely in the ballpark. It was just hard because I never achieved what I thought was blooming, and no patterns (eg needle pulse) seemed to distort no matter what I had it set at. It's also at a setting where all the ramp patterns look like nothing is being clipped or excessively white.

    As for my 16:9 dilemma, I think in some cases you do see two sets of bars even if your blacks are 100% accurate. I mean, 100% black and a TV screen in an "off" position might not necessarily be the same shade all the time.
     

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