Getting the grey scale corrected....

Discussion in 'Archived Threads 2001-2004' started by Maximil, Nov 6, 2001.

  1. Maximil

    Maximil Agent

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    I'm still fiddling with my CUTs and DRVs, trying to get the scale looking uniform after performing the Herman-TLV tweak on my 55HX70.
    Using AVIA and "eye balling" I have the upper and lower ends looking good, but I can't seem to get the green out of the middle (around 50-70 IRE).
    Increasing the R&B Cuts gives me a purple dark end. Increasing the R&B Drvs does the same to the white end.
    Any ideas??
    My settings:
    BDRV: 12
    RDRV: 2D
    BCUT: 3A
    GCUT: 80
    RCUT: 7A
    BRT: A2
     
  2. Guy Kuo

    Guy Kuo Supporting Actor

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    It is pretty common for the guns not to completely track with each other throughout the entire grayscale. You only have control of the two ends and can't really directly change the middle of the response curves. The mistracking is particularly bad on CRT RPTV's and FPTV's if the blue gun is maximally beam focused and you are asking the display to output a good amount of light. The choice then is to take overall contrast down or slightly underfocus the blue gun.
    If you are using AVIA, I suggest you turn color saturation all the way down before doing any grayscale adjustments. There is about 300K of coloration which crept into the darker windows during MPEG compression. Given that you cannot fully achieve tracking, most calibrators will select two end points which are closer together and accept some error on the extremes. For instance you might select the 30 and 90 IRE windows as the upper and lower ones to examine during calibration.
    The process is MUCH more accurately and easily done with a colorimeter. At the very least you should be using an optical comparator as a color reference against which to visually check the color you are producing.
    ------------------
    Guy Kuo
    www.ovationsw.com
    Ovation Software, the Home of AVIA DVD
     
  3. Maximil

    Maximil Agent

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    Thank you for the helpful insight and suggestions Guy, I'll give it a try. What's a good optical comparator?
     
  4. Guy Kuo

    Guy Kuo Supporting Actor

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    The cheapest solution which would be pretty accurate is to shine a Lumichrome 1xx D6500 fluourescent bulb onto a Koday gray card. You can find the bulb on the web but it is very difficult to get in single quantities. http://www.cinemaquestinc.com/ideal_lume.htm has it in a fixture.
    I suggest this particular bulb as other "6500" full spectrum bulbs will have a tendency to have too much or too little green. This one gets it right, but is just slightly too blue. It's the closest one out there.
    If you have a bigger budget then you could go after a commercial comparator but expect to pay quite a bit more. For a professional calibrator it would be worth it, but for home use, I'm not so sure.
    ------------------
    Guy Kuo
    www.ovationsw.com
    Ovation Software, the Home of AVIA DVD
     
  5. Maximil

    Maximil Agent

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    Hmmm so that would be for setting the white end?
    I happen to have my PC & monitor right next to my TV. The monitor looks way better greyscale wise than my TV. So would finding a good JPEG to display on the moinior for comparison be another way to do this?
    I tried your suggestion last night. Using 30-90 IRE as end points still did not look right, I just can't stand blue tinged dark scenes. I think I will start over with the screen trimpots, since I know that my doing the Herman-TLV tweak put me in this predicament. The scale looked much more uniform before I tried the tweak. I was just under the impression that no matter where you leave the trimpots set (within reason), things can be set perfectly using the CUTs and DRVs...
     

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