Setting Contrast/Picture Control

Discussion in 'Archived Threads 2001-2004' started by Guy Kuo, Feb 11, 2003.

  1. Guy Kuo

    Guy Kuo Supporting Actor

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    The short answer is..... set contrast to the LOWEST setting which still allows white to look white.

    The long answer follows. This was written for AVIA but the basic principles still apply. Adjusting for just short of blooming is not the goal. Blooming is the point which should be thought as the red line for the electron guns. Just as you shouldn't keep your engine just below its red line in daily usage, you shouldn't do that with the contrast control of a CRT display. The on disc instructions for HTT and AVIA simply didn't allow time for as complete a discussion as follows. For those really wishing to do it as "right" as possible without instrumentation consider the following as superceding the on disc "instruction for the masses" on HTT, AVIA, and DVE discs....

    ......
    Now for the more nebulous white level setting. You're quite right in noting that white level is more difficult to set. There isn't a hard end point at which to aim. Without instrumentation, the idea isn't to hit a specific light output level, but to remain below the point at which CRT wear and image fidelity worsen. Even with a light meter, one must still pay attention to colorimetry problems as well as absolute light output level. Since most of use don’t' run around with a colorimeter, we look for the point at which blooming appears because that is near the point of increased wear. Once the blooming point is determined on your display, it is taken as the maximal NOT desired setting for white level. Then, we set a viewing level somewhere below that point.
    It appears that you are having difficulty detecting when blooming is happening on your display. The best advice I can give is to be VERY close to your screen -- perhaps two feet -- when looking for blooming. Doing this from normal viewing distance doesn't work as well. Turn white level down to a ridiculously low level. Make white actually appear gray. You should see distinct scan lines making up the picture. If you don't see sharp, distinct scan lines, then something is amiss with the display's focus adjustments. If that is the case, it needs to be serviced. You can't see the blurring effect of blooming if the beam is already defocused at low output levels.
    I'll assume you're viewing HTT's Contrast Pattern or AVIA's Needle Pulses + Steps pattern or the Black Bars + Log Steps pattern. Look very carefully at the right edge of the rectangles which make up the steps pattern. Pay particular attention to the white rectangle and the one just below it. Turn up white level until you see the width of the white rectangle grow slightly larger. That is the point of blooming. Remember that point. Don't ever go over that point.
    Now that you have found the maximum allowable white level. It's time to set viewing level. The lower, the better for CRT life, but you also need enough output to have a decent picture. Once again back white level down to a ridiculous level (making white look definitely gray). Increase white level until white appears white, but stay below the blooming limit which was previously determined. With any luck, white looks white before the point of blooming. If not, then your best course is to REDUCE AMBIANT LIGHT. It is better to adapt your eyes to make the lower level appear white than to overdrive the display to compete with excessive room light. This allows for best image fidelity within the limits of the display's capability. Some people will never control room light and turn up their displays beyond the point of blooming in order to view them in high ambient light. One is free to do so, but one must remember that this shortens display life and compromises image fidelity
     
  2. Steve Schaffer

    Steve Schaffer Producer

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    Thanks Guy!! This is how I've been using AVIA to set white level all along and I've never had burn-in on either of my rptvs.

    I am fortunate in that I can exercise some control over room light even during the day, if I couldn't you can bet I'd be using a cheapo direct view for watching the Today show instead of my rptv.

    One other thing I've found helpful with rptvs is to use the black bars with half gray pattern for adjusting black level--minimizes the effect of internal set reflections on the setting.
     
  3. John-Miles

    John-Miles Screenwriter

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    maybe i just missed it on the avia disc, but one thing there which I just found helpful was the note to sit very close when doing this. thusfar I have done all my calibrations from normal viewing distance, i will have to go back and check this again.
     
  4. Doug_B

    Doug_B Screenwriter

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    Guy,

    Any alterations to the above or alternate recommendations for digital displays?

    Thanks.

    Doug
     
  5. Guy Kuo

    Guy Kuo Supporting Actor

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    Digital displays like LCD's, LCOS, and DLP add a little twist to things. There is no lifespan problem with going to a higher contrast level, but instead one needs to be mindful of causing clipping of the brighter portions of the video signal. You should pay attention to the moving white bars in AVIA or HTT. Those are just barely below the legal max white level for DVD. If you adjust the contrast too high the moving bars disappear due to clipping. Try to keep below that point on the digital displays. Also pay attention to how grayscale consistency as you increase contrast setting. The log steps in HTT's contrast pattern should stay the same color, but on some displays you see a color change when contrast is set too high.

    Plasma I'd think about in a slightly different manner. You need to pay attention to how grayscale shifts and clipping as with the LCD, LCOS, and DLP displays, but there is the additional issue of display life. With plasma, unlike the other three, higher contrast can decrease lifespan. So, with plasma, I'd treat it like CRT and keep contrast as low as acceptable for best display life span.
     
  6. Gregg Loewen

    Gregg Loewen Video Standards Instructor, THX Ltd.
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    Gregg Loewen
    Guy,

    thanks

    Another thread for the Archive.

    regards

    Gregg
     

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