At what IRE should I tweak my RPTV's convergence?

Discussion in 'Displays' started by Dave H, Jun 5, 2003.

  1. Dave H

    Dave H Producer

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    I have been tweaking it at 100 IRE (using Avia) but have been told to be careful because there is some blooming at that level, making it deceiving to tell --- would 50 IRE be better? My TV has been ISF'd - so my white level is where it should be.
     
  2. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

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    Greetings

    Depending on the set, the convergence grid brightness/contrast is preset regardless of calibration.

    Regards
     
  3. Jeremy Anderson

    Jeremy Anderson Screenwriter

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    Michael's right -- most are preset. Hitachis let you control the DCU contrast, however, and I've found that to be very helpful for getting things lined up better. It also limits potential burn-in from having the convergence grid on the screen for a long time (which admittedly isn't a big problem anyway unless you're doing a from-scratch convergence).
     
  4. Tommy Ceez

    Tommy Ceez Second Unit

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    You will have to do service menu type (I dont know what brand yor using) tweaks with avia. The built in convergence grids cannot be beat for ease of use.
     
  5. Dave H

    Dave H Producer

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    I am using Avia's crosshatch pattern at 100 IRE exclusively - selecting a blank, black screen (output mode - you know how you have Video1, Video2, DVD, VHS, etc.) -- so the TV's grid is not appearing (which is at about 50 IRE). Avia allows you to display a crosshatch at three different IRE's. My TV is a Sony KP-61V80.

    So, I can converge without using the service menu's crosshatch.

    Using 100 IRE allows me to see the colors better it appears.
     
  6. Jeremy Anderson

    Jeremy Anderson Screenwriter

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    But how are you actually adjusting convergence without having the screen's internal crosshatches displayed? I don't think you can do that on ANY RPTV. If you're just displaying a crosshatch pattern on Avia, you're not actually adjusting convergence. Sure, you can double-check convergence by using those patterns and then use the set's convergence grid to adjust each point... but you can't actually adjust using Avia. The patterns on Avia will let you do a quick double-check of your convergence and geometry, but the colors should line up regardless of which of the three patterns you're using (regardless of IRE).

    Maybe I'm not understanding what you're doing... How exactly are you adjusting convergence using Avia?
     
  7. Allan Jayne

    Allan Jayne Cinematographer

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    After you lower the contrast to be sure there is no blooming, and still lower to forestall burning of the CRT's, there is no problem using 100 IRE test patterns.

    There is one problem that relates to the IRE value to do convergence with, and I don't know the solution. Some TV sets' convergence will drift with the average brightness of the raster (or entire picture showing). I would think it is best to do convergence by having an average raster brightness two thirds of your maximum (said maximum being 100 IRE solid white but with the contrast at about a third of full scale for RPTV or FPTV). Except that the best convergence test pattern has small light lines or spots on a dark backgroudn so you can't get an overall average brightness that high. Catch 22.

    The IRE value has to do with the part of the input waveform representing the white line or dot or patch (expressed in volts for component video). How bright it appears on the screen (expressed in foot lamberts) depends on the brightness and contrast settings among other things.

    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  8. JohnnyG

    JohnnyG Screenwriter

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    Overall, I really don't think there's a correct answer here. Convergence WILL change somewhat with the average picture level (APL). So no matter where you perfect the convergence, it'll still be off at other APLs.
     
  9. Dave H

    Dave H Producer

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