Guy, some help with Avia's Needle Pulse

Discussion in 'Archived Threads 2001-2004' started by Tony_Pat, Mar 17, 2002.

  1. Tony_Pat

    Tony_Pat Agent

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    Hi Guy. I've used Avia on a number of TVs over the years with good results, but I noticed something odd with my new Sony 32FV27. On the Needle Pulse with Steps display I can't get either the black lines to bend, or make the white bars disappear (indicating White Clipping). It seems even with the Picture control max'ed out I can't even really tell if there is blooming on the white box in the step pattern. I made sure VSM is set to OFF before starting. Is it possible that Sony got smart and now max'ing out Picture does not cause blooming? It got to where I kept the control up toward the max for several seconds, trying in vain to find one indication that I needed to back down. In theory, would I have seen the White Bars disappear before seeing blooming in the top box? Which happens first?

    I wound up setting it to about 70% on the scale, only because I have it ingrained in my head that it's a bad thing to have it set to 100%.
     
  2. Allan Jayne

    Allan Jayne Cinematographer

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    If the line in the needle pattern does not bend, your TV set has a more robust power supply than most, or the maximum contrast on the scale is somewhat below what the phosphors could conceivably deliver in terms of brightness. On some TV sets the power supply is so poorly regulated that the line starts to bend even 1/4 way up the contrast scale. In this case you can't really use the needle bending test but instead have to rely on just the blooming test for your calibration.]
    If you can't tell the blooming point, try using a step gray scale test and consider the maximum contrast as the point where the second to lightest bar cannot be distinguished from the lightest bar.
    The life of the TV set will be lengthened if you reduce the contrast much below the blooming point or needle bend point (whichev er is less) and finish the calibrations around this constraint.
    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  3. Guy Kuo

    Guy Kuo Supporting Actor

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    No the white bars would disappear on a digital display, not a CRT display. The following should help....

    .....Unlike black level, there isn't an invariant end point a pattern can fix on the screen against which to compare the rest of the pattern. Blackest possible black doesn't change on the display, but there isn't a special signal one can send to a display to make it display the brightest safe white so we have to force you to do more work.

    The idea is to remain below the point at which CRT wear and image fidelity worsen. With a video light meter we could have you set things to a target value, but since most of us don?t run around with a colorimeter, we have you 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 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.

    Don't fret if you STILL don't see blooming. It isn't a goal but something it would be nice to know not to exceed. You can still get to the right place for your display in the next step.

    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.
     
  4. Tony_Pat

    Tony_Pat Agent

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  5. Guy Kuo

    Guy Kuo Supporting Actor

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    In the short time you've had the set, I doubt you did anything bad to it long term. Relax. Go watch a movie.
     
  6. Tony_Pat

    Tony_Pat Agent

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    Just finished watching The Third Man! [​IMG]
     

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