Avia - "Black bars + Log Steps" pattern in Ch. 7 - optimal for dark viewing?

Discussion in 'Archived Threads 2001-2004' started by Dave H, Dec 21, 2001.

  1. Dave H

    Dave H Producer

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    Someone recently told me that in Ch. 7 of Avia (under Black and White Levels) that the "Black Bars + Log Steps" pattern
    is actually the best way to set black level in a dark room.
    I also was told that I should be able to see both bars - just barely seeing the faintest one.
    Guy, your thoughts? [​IMG]
    Dave
     
  2. Allan Jayne

    Allan Jayne Cinematographer

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    Follow the same guidelines regardless if you intend to do most of your viewing with the room lights dimmed.
    If you recalibrate with the room light level different, your calibration settings will be different. If you view under differing room light levels on different occasions, your calibration will always be a compromise, do it when the room light level is in between.
    Whether you want to see blacker than black details that some DVD's have (adjust so both bars are still visible) it is your choice. When the darker bar just blends into the background, the black level is set to normal black (IRE 7.5).
    If the room light level is high, the TV might not adjust far enough for the blacker than black bar (and blacker than black details in movies possessing same) to be readily distinguished amidst room light hitting the screen and reflections.
    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  3. Jay Mitchosky

    Jay Mitchosky Producer

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    Guy will be able to clear this up, but if you're looking for some immediate thoughts here goes...

     
  4. Guy Kuo

    Guy Kuo Supporting Actor

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    Jay pretty much has it covered.

    The black bars in the various patterns AVIA patterns which have them (black bars + various half brightness, black bars + log scale, needle pulses, color bars) are all encoded at the same signal level. The darker bar is 1 IRE above true black. The lighter one is 2 IRE above above true black. The thing that changes is the average picture level of the pattern. Some of the patterns are quite bright, others like the black bars + log steps are low APL. The lowest APL pattern with black bars one is the black bars alone. The black bars are on patterns with various level APL levels so you can....

    a. Determine how well your display holds black level constant as APL changes.

    b. Select a pattern with an APL which works well for your viewing situation and equipment.

    Here's where the need to supply generic directions which work well for most people comes in. We know that virtually all consumer displays do not hold black level truely constant with varying APL. So basically, no matter what you set your black level at there will always be some sort of compromise as APL changes. The black bars + half gray pattern has an APL level with attains a reasonable compromise because it puts the display under an average APL load.

    The darkest black bar is actually very dimly visible when black is adjusted to be exactly on and the display has near perfect cut off characteristics. In practice, the cut off of the device isn't so clean that the darkest bar will be visible without lighting up black. Further confusing visual adjustment is the tendency of RPTV's to scatter light from other portions of the screen, obscuring darker portions of a picture. So for many displays, the darker bar isn't easily seen when black level is just right. On the other hand you don't want to accidentally make black too black and that's where the 2 IRE lighter black bar is important. If that is visible you know that your black leve is adjusted such that at least the 2 IRE is visible above black. You definitely don't want to go darker than that so we have you make sure that the lighter one is visible. The darker one may or may not be visible. Ideally it is but it is really hard to see.

    In the end, you get to decide how to compromise on your own display. Are you someone who wants to see shadow details despite making dark scenes glow instead of being super dark? Are you someone who craves the depth whis given by a true black black? That preference will guide you in selecting the APL level pattern for using black bars. If you like super dark blacks you'd use a low APL pattern. If you want shadow details to always be visible use a high APL pattern. If you are in between, use a mid APL pattern.

    On displays which actually hold black level constant, it doesn't matter which pattern you use. That's pretty much the definition of a display with perfect black level retention. However, light scatter can still obscure the visibility of the black bars, so a low APL pattern or staring directly into projection optics can yield more accurate results. It all hinges on how well your display holds black level constant and how much light scatter obscures your vision.

    An oh, yes, as mentioned above room lighting has a big effect on your ability to see near black details so calibrate at the viewing lighting condition.
     
  5. Dave H

    Dave H Producer

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    Guy,

    Let me see if I have this straight.

    The ISF tech told me my TV holds black "pretty well" for a commercial set. However, I do see some light scatter or halo from the (standard) black bar + grey half pattern.

    Now, I like to have a compromise between black and shadows (but still leaning more toward black). So, would using a the Black + log step pattern barely showing the darkest bar be ideal for me?
     
  6. Guy Kuo

    Guy Kuo Supporting Actor

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    Probably yes, but in truth that is a decision you make regarding your own preferences. All I can do is lay out what the ramifications as above.
     
  7. Dave H

    Dave H Producer

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    I just want to make sure I'm applying correctly what was stated above to meet my preferences. Thanks.
     

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